Abstract: BACKGROUND AND PURPOSE: Complete ophthalmoplegia, the combination of bilateral ptosis with loss of all extraocular movements, is rarely a consequence of ischemic stroke. We describe 3 patients who had complete ophthalmoplegia as a manifestation of bilateral paramedian midbrain-thalamic infarction, and we discuss possible pathophysiologic mechanisms. Summary of Cases- Three patients presented with coma. All had complete ophthalmoplegia that initially persisted despite improvement or fluctuation in their other deficits. MRI revealed bilateral paramedian midbrain-thalamic infarction. Two patients died, with the ophthalmoplegia remaining unchanged before death. The surviving patient had a progressive improvement in ocular abduction but persisting third nerve and vertical gaze palsies. CONCLUSIONS: Complete ophthalmoplegia is an unusual sign of bilateral paramedian midbrain-thalamic infarction. The ophthalmoplegia could result from combined third nerve, pseudoabducens, and vertical gaze palsies.
Abstract: BACKGROUND: Quantitative head impulse test (HIT) measures the gain of the angular vestibulo-ocular reflex (VOR) during head rotation as the ratio of eye to head acceleration. Bedside HIT identifies subsequent catch-up saccades after the head rotation as indirect signs of VOR deficit. OBJECTIVE: To determine the VOR deficit and catch-up saccade characteristics in unilateral vestibular disease in response to HIT of varying accelerations. METHODS: Eye and head rotations were measured with search coils during manually applied horizontal HITs of varying accelerations in patients after vestibular neuritis (VN, n = 13) and unilateral vestibular deafferentation (UVD, n = 15) compared to normal subjects (n = 12). RESULTS: Normal VOR gain was close to unity and symmetric over the entire head-acceleration range. Patients with VN and UVD showed VOR gain asymmetry, with larger ipsilesional than contralesional deficits. As accelerations increased from 750 to 6,000 degrees /sec(2), ipsilesional gains decreased from 0.59 to 0.29 in VN and from 0.47 to 0.13 in UVD producing increasing asymmetry. Initial catch-up saccades can occur during or after head rotation. Covert saccades during head rotation are most likely imperceptible, while overt saccades after head rotation are detectable by clinicians. With increasing acceleration, the amplitude of overt saccades in patients became larger; however, initial covert saccades also became increasingly common, occurring in up to about 70% of trials. CONCLUSIONS: Head impulse test (HIT) with high acceleration reveals vestibulo-ocular reflex deficits better and elicits larger overt catch-up saccades in unilateral vestibular patients. Covert saccades during head rotation, however, occur more frequently with higher acceleration and may be missed by clinicians. To avoid false-negative results, bedside HIT should be repeated to improve chances of detection.
Abstract: OBJECTIVE: Patients with superior canal dehiscence (SCD) have large sound-evoked vestibular reflexes with pathologically low threshold. We wished to determine whether a recently discovered measure of the vestibulo-ocular reflex-the ocular vestibular evoked myogenic potential (OVEMP)-produced similar high-amplitude, low-threshold responses in SCD, and could differentiate patients with SCD from normal control patients. METHODS: Nine patients with CT-confirmed SCD and 10 normal controls were stimulated with 500 Hz, 2 ms tone bursts and 0.1 ms clicks at intensities up to 142 dB peak SPL. Conventional VEMPs were recorded from the ipsilateral sternocleidomastoid muscle to determine threshold, and OVEMPs were recorded from electrode pairs placed superior and inferior to the eyes. Three-dimensional eye movements were measured with scleral dual-search coils. RESULTS: In patients with SCD, OVEMP amplitudes were significantly larger than normal (p<0.001) and thresholds were pathologically low. The n10 OVEMP in the contralateral inferior electrode became particularly large with increasing stimulus intensity (up to 25 microV) and with up-gaze (up to 40 microV). Sound-evoked (slow-phase) eye movements were present in all patients with SCD (vertical: upward; torsional: upper pole away from the affected side; and horizontal: towards or away from the affected side), but began only as the OVEMP response became maximal, which is consistent with the surface potentials being produced by activation of the extraocular muscles that generated the eye movements. CONCLUSIONS: OVEMP amplitude and threshold (particularly the contralateral inferior n10 response) differentiated patients with SCD from normal controls. Our findings suggest that both the OVEMPs and induced eye movements in SCD are a result of intense saccular activation in addition to superior canal stimulation.
Abstract: OBJECTIVE: Patients with superior canal dehiscence (SCD) typically have enhanced sound-evoked vestibular reflexes, such as vestibulo-collic and vestibulo-ocular reflexes. We wished to investigate whether sound-evoked lower limb EMG responses and postural sway are also enhanced in this condition. METHODS: Eight patients with CT confirmed SCD (11 affected ears) and 8 age-matched normal controls participated. Three sound-evoked responses were measured; vestibulo-collic reflexes (i.e. vestibular-evoked myogenic potentials, VEMPs), lower limb vestibulo-spinal reflexes and body sway (centre of pressure in mm). Sound stimuli were 500Hz air-conducted tone bursts of varying lengths (VEMPs: 2ms; vestibulo-spinal: 20ms; sway: 1s and 200ms) set at fixed levels above each subject's VEMP threshold. RESULTS: SCD patients had very large VEMP and vestibulo-spinal responses following high intensity stimulation, but at the matched intensity of 15dB above threshold amplitudes were similar in both SCD patients and controls. The amplitude of both responses increased linearly with increasing stimulus intensity in both groups. Large ( approximately 20mm), stereotyped sway responses were present in only one (atypical) patient with high intensity stimulation. Small ( approximately 2mm) sway responses were present in the remaining patients, and began immediately following the vestibulo-spinal responses. CONCLUSIONS: Despite the presence of large vestibular reflexes, there is usually very little body sway in response to loud sounds in SCD patients. SIGNIFICANCE: Large short-latency vestibulo-spinal reflexes in SCD do not necessarily evoke large sway responses.
Abstract: Taps to the forehead on the midline, at the hairline (Fz), with a reflex hammer or powerful bone conduction vibrator caused short-latency surface potentials from beneath both eyes in all healthy subjects. The earliest negative responses were invariably absent from the eye contralateral to the side of a previous vestibular nerve section but were preserved despite sensorineural hearing loss. These responses probably reflect vestibular function via crossed otolith-ocular pathways.
Abstract: We describe two immunocompetent patients with tuberculous cranial pachymeningitis. Both patients underwent biopsy after focal dural thickening was identified on MRI. Histopathologic examination of tissue revealed necrotizing granulomatous inflammation. PCR for Mycobacterium tuberculosis DNA was negative on CSF but positive on tissue. Both patients responded to antituberculous therapy. Although uncommon as a cause of cranial pachymeningitis, tuberculosis should be considered, since it responds well to treatment.
Abstract: Eye movement disorders are rarely reported in vitamin B12 deficiency. We describe two cases with eye movement disorder and vitamin B12 deficiency; one with bilateral internuclear ophthalmoplegia and the other with downbeat nystagmus. Both of the patients received replacement therapy but their eye movement disorders did not respond to treatment. We also review the nine previously reported cases.
Abstract: We report a patient who presented with acute painful monocular visual loss reminiscent of idiopathic optic neuritis. After treatment with corticosteroids was commenced, an anterior clinoid mucocele causing compressive optic neuropathy was demonstrated on imaging studies. The diagnosis was proven histopathologically following excision of the lesion via craniotomy. Although very rare as a cause of optic neuropathy, anterior clinoid mucocele should be excluded by adequately imaging the optic canal, as visual prognosis is poor if surgical decompression is not performed in a timely fashion.
Abstract: BACKGROUND: An enlarged, low-threshold click-evoked vestibulo-ocular reflex (VOR) can be averaged from the vertical electro-oculogram in a superior canal dehiscence (SCD), a temporal bone defect between the superior semicircular canal and middle cranial fossa. OBJECTIVE: To determine the origin and quantitative stimulus-response properties of the click-evoked VOR. METHODS: Three-dimensional, binocular eye movements evoked by air-conducted 100-microsecond clicks (110 dB normal hearing level, 145 dB sound pressure level, 2 Hz) were measured with dual-search coils in 11 healthy subjects and 19 patients with SCD confirmed by CT imaging. Thresholds were established by decrementing loudness from 110 dB to 70 dB in 10-dB steps. Eye rotation axis of click-evoked VOR computed by vector analysis was referenced to known semicircular canal planes. Response characteristics were investigated with regard to enhancement using trains of three to seven clicks with 1-millisecond interclick intervals, visual fixation, head orientation, click polarity, and stimulation frequency (2 to 15 Hz). RESULTS: In subjects and SCD patients, click-evoked VOR comprised upward, contraversive-torsional eye rotations with onset latency of approximately 9 milliseconds. Its eye rotation axis aligned with the superior canal axis, suggesting activation of superior canal receptors. In subjects, the amplitude was less than 0.01 degrees, and the magnitude was less than 3 degrees/second; in SCD, the amplitude was up to 60 times larger at 0.66 degrees, and its magnitude was between 5 and 92 degrees/second, with a threshold 10 to 40 dB below normal (110 dB). The click-evoked VOR magnitude was enhanced approximately 2.5 times with trains of five clicks but was unaffected by head orientation, visual fixation, click polarity, and stimulation frequency up to 10 Hz; it was also present on the surface electro-oculogram. CONCLUSION: In superior canal dehiscence, clicks evoked a high-magnitude, low-threshold, 9-millisecond-latency vestibulo-ocular reflex that aligns with the superior canal, suggesting superior canal receptor hypersensitivity to sound.
Abstract: Cathodal galvanic currents activate primary vestibular afferents, whereas anodal currents inhibit them. Pulsed galvanic vestibular stimulation (GVS) was used to determine the latency and initiation of the human vestibuloocular reflex. Three-dimensional galvanic vestibuloocular reflex (g-VOR) was recorded with binocular dual-search coils in response to a bilateral bipolar 100-ms rectangular pulse of current at 0.9 (near-threshold), 2.5, 5.0, 7.5, and 10.0 mA in 11 normal subjects. The g-VOR consisted of three components: conjugate torsional eye rotation away from cathode toward anode; vertical divergence (skew deviation) with hypertropia of the eye on the cathodal and hypotropia of the eye on the anodal sides; and conjugate horizontal eye rotation away from cathode toward anode. The g-VOR was repeatable across all subjects, its magnitude a linear function of the current intensity, its latency about 9.0 ms with GVS of >or=2.5 mA, and was not suppressed by visual fixation. At 10-mA stimulation, the g-VOR [x, y, z] on the cathodal side was [0.77 +/- 0.10, -0.05 +/- 0.05, -0.18 +/- 0.06 degrees ] (mean +/- 95% confidence intervals) and on the anodal side was [0.79 +/- 0.10, 0.16 +/- 0.05, -0.19 +/- 0.06 degrees ], with a vertical divergence of 0.20 degrees . Although the horizontal g-VOR could have arisen from activation of the horizontal semicircular canal afferents, the vertical-torsional g-VOR resembled the vestibuloocular reflex in response to roll-plane head rotation about an Earth-horizontal axis and might be a result of both vertical semicircular canal and otolith afferent activations. Pulsed GVS is a promising technique to investigate latency and initiation of the human vestibuloocular reflex because it does not require a large mechanical apparatus nor does it pose problems of head inertia or slippage.
Abstract: Research into vestibular responses to sound has evolved in four stages. The first, largely the work of Tullio in the 1920s, involved inspection of the eye, head, and postural responses to sound of alert animals with surgical fenestrae into various parts of the bony labyrinth. The second, begun in 1964 by Bickford and his group and continued by our group and then by others in the last 10 years, involves the measurement of evoked myogenic potentials to air-conducted and bone-conducted clicks and tones in normal humans. The third, begun by Mikaelian at about the same time as Bickford and continued by McCue, our group, and others, involves electrophysiological recordings of primary vestibular afferent neuron responses to sound in anesthetized animals. The fourth involves measurements of vestibulo-ocular responses to sound in humans with the Tullio phenomenon. It was begun by Minor and his group in 1998 with the observation that sound-induced nystagmus in humans, the Tullio phenomenon, aligned with the rotation axis of the superior semicircular canal. They then showed a defect in the temporal bone between the apex of the superior semicircular canal and the middle cranial fossa, which was the cause of most, if not all, cases of sound-induced nystagmus. Here some of the key observations made in each of these four stages are reviewed.
Abstract: BACKGROUND: The head-impulse test, which is sensitive and specific for detecting severe unilateral peripheral vestibulopathy, is an accepted part of the neurological examination, especially in patients with vertigo and balance disorders. OBJECTIVE: To discover if the head-impulse test is just as useful diagnostically when patients are asked to rotate their own heads, the active head-impulse test, rather than when the clinician does so as in the standard passive head-impulse test. METHODS: Clinical observation of compensatory saccades and search coil measurement of compensatory eye rotations, during active and passive horizontal head-impulses in 6 patients with total unilateral vestibular deafferentation. RESULTS: Clinical observation showed the expected compensatory saccades with rotations toward the side with the lesion with passive head-impulses but not with active head-impulses. Search coil recordings revealed 2 reasons for this. With active head-impulses not only was vestibulo-ocular reflex gain higher, but compensatory saccade latency was shorter resulting in an occult saccade that occurred during, rather than after, head rotation. CONCLUSIONS: Passive head-impulses are necessary to detect a severe unilateral peripheral vestibulopathy; active head-impulses will produce a false-negative result.
Abstract: Vertigo is an illusion of rotation due to a disorder of the vestibular system, almost always peripheral. In the history it must be distinguished from pre-syncope, seizures and panic attacks. A single attack of acute, isolated spontaneous vertigo lasting a day or more is due either to vestibular neuritis or cerebellar infarction; distinguishing between the two requires mastery of the head impulse test. Recurrent vertigo is mostly due to benign paroxysmal positioning vertigo (BPPV), Meniere's disease or migraine. With a good history, a positional test, an audiogram and a caloric test, it is usually possible to distinguish between these. BPPV is the single most common cause of recurrent vertigo and can usually be cured immediately with a particle repositioning manoeuvre. Posterior circulation ischaemia very rarely causes isolated vertigo attacks and when it does the attacks are brief and frequent and the history is short.
Abstract: OBJECTIVE: To describe the spatial and temporal characteristics of benign positional nystagmus (BPN) subtypes in benign positional vertigo (BPV) due to vestibular lithiasis affecting one or more semicircular canals (SCCs). BACKGROUND: Activation of SCC receptors by sequestered otoconia, either freely moving (canalithiasis) or cupula-adherent (cupulolithiasis) during head position changes with respect to gravity, is the accepted cause of BPV. Although accurate identification and interpretation of BPN is critical to BPV therapy, no rigorous, kinematically correct three-dimensional spatio-temporal analysis of BPN in all its forms exists. METHODS: Using dual-search scleral coils, the authors recorded BPN provoked by Dix-Hallpike or supine ear-down test in a two-axis whole-body rotator in 44 patients with refractory BPV. To localize the SCC affected, BPN rotation axes were compared to SCC axes, axes orthogonal to average SCC planes. RESULTS: Sixteen patients had upbeat, geotropic-torsional BPN in the Dix-Hallpike test to one side and five to both sides, with BPN rotation axes clustered around the lowermost posterior SCC axis. Seven had direction-changing horizontal BPN, three geotropic (canalithiasis) and four apogeotropic (cupulolithiasis), with rotation axes around the lowermost and uppermost horizontal SCC axis. Seven had predominantly downbeating BPN with rotation axes clustered around one superior SCC axis. Nine had upbeat, horizontal-torsional BPN with rotation axes located between posterior and horizontal SCC axes of the lowermost ear suggesting simultaneous lithiasis in both SCCs. BPN vector-guided repositioning therapy was successful in 43 patients. CONCLUSION: Benign positional vertigo can affect one or more semicircular canals and three-dimensional recording with vector analysis of the benign positional nystagmus (BPN) can guide canalith repositioning therapy especially in refractory cases with atypical BPN.
Abstract: OBJECTIVE: To assess the pulse rate and the respiratory rate responses to head-down tilt of the whole body in the plane of the posterior canals in healthy subjects and in patients with benign paroxysmal positional vertigo (BPPV). BACKGROUND: Although BPPV attacks are usually accompanied by autonomic symptoms, there are no studies assessing autonomic responses during triggering maneuvers for BPPV, neither in healthy subjects nor in patients. METHODS: We evaluated nine healthy subjects and four BPPV patients (3 unilateral and 1 bilateral). Using a two-axis rotator, from an upright position they were rotated 135 degrees backwards to head-down tilt, either in the plane of the right or the left posterior canal. RESULTS: In healthy subjects, head-down tilt always induced a significant decrease of the pulse rate, which was similar after rotation to the right and to the left posterior canals. This response was observed in patients with unilateral BPPV only when they were rotated toward the nonaffected side, and it was not evident when they were rotated toward the affected side (p < 0.025). In the patient with bilateral BPPV, no change of the pulse rate was observed after rotation toward the right or to the left posterior canal. Although, in all the patients, the respiratory rate increased during the tilt, a similar increase was observed in two healthy subjects. CONCLUSION: After rotation in the plane of the affected semicircular canal, BPPV can interfere with the cardiac response to head-down tilt of the whole body.
Abstract: The pathophysiology of PTS including idiopathic intracranial hypertension or 'BIH', remains controversial. The older literature frequently referred to pathology in the cerebral venous drainage but more modern imaging techniques (CT and early MR) failed to reveal gross venous pathology. The role of impaired cranial venous outflow has recently been re-examined in the light of new methods of investigation (advanced MR venography and direct microcatheter venography with manometry) and of treatment (venous sinus stenting). Venous sinus obstruction in PTS is a more common factor in the pathogenesis of the condition than previously recognised. Venous obstruction may be primary, that is, it is the underlying aetiological factor in PTS. Venous sinus obstruction may also be secondary to raised CSF pressure which may exacerbate problems with intracranial compliance and raised CSF pressure. Early experience with venous stenting suggests that it may be a helpful treatment for patients with PTS but more experience and longer follow-up is required to define the subgroups of patients for whom it is most appropriate.
Abstract: HYPOTHESIS: That disease or dysfunction of vestibular end organs in human patients will reduce or eliminate the contribution of the affected end organs to the total eye-movement response to DC surface galvanic vestibular stimulation (GVS). BACKGROUND: It was assumed that DC GVS (at current of 5 mA) stimulates all vestibular end organs, an assumption that is strongly supported by physiological evidence, including the activation of primary vestibular afferent neurons by galvanic stimulation. Previous studies also have described the oculomotor responses to vestibular activation. Stimulation of individual semicircular canals results in eye movements parallel to the plane of the stimulated canal, and stimulation of the utricular macula produces changes in ocular torsional position. It was also assumed that the total three-dimensional eye-movement response to GVS is the sum of the contributions of the oculomotor drive of all the vestibular end organs. If a particular vestibular end organ were to be diseased or dysfunctional, it was reasoned that its contribution to the GVS-induced oculomotor response would be reduced or absent and that patients thus affected would have a systematic difference in their GVS-induced oculomotor response compared with the response of normal healthy individuals. METHODS: Three-dimensional video eye-movement recording was carried out in complete darkness on normal healthy subjects and patients with various types of vestibular dysfunction, as diagnosed by independent vestibular clinical tests. The eye-movement response to long-duration bilateral and unilateral surface GVS was measured. RESULTS: The pattern of horizontal, vertical, and torsional eye velocity and eye position during GVS of patients independently diagnosed with bilateral vestibular dysfunction, unilateral vestibular dysfunction, CHARGE syndrome (semicircular canal hypoplasia), semicircular canal occlusion, or inferior vestibular neuritis differed systematically from the responses of normal healthy subjects in ways that corresponded to the expectations from the conceptual approach of the study. CONCLUSION: The study reports the first data on the differences between the normal response to GVS and those of patients with a number of clinical vestibular conditions including unilateral vestibular loss, canal block, and vestibular neuritis. The GVS-induced eye-movement patterns of patients with vestibular dysfunction are consistent with the reduction or absence of oculomotor contribution from the end organs implicated in their particular disease condition.
Abstract: PURPOSE: As a normal subject looks from far to near, Listing's plane rotates temporally in each eye. Since Listing's plane relates to the control of torsional eye position, mostly by the oblique eye muscles, the current study was conducted to test the hypothesis that a patient with isolated superior oblique palsy would have a problem controlling Listing's plane. METHOD: Using the three-dimensional scleral search coil technique, binocular Listing's plane was measured in four patients with congenital and in four patients with acquired unilateral superior oblique palsy during far- (94 cm) and near- (15 cm) viewing. The results were compared to previously published Listing's plane data collected under exactly the same conditions from 10 normal subjects. RESULTS: In patients with unilateral superior oblique palsy, either congenital or acquired, Listing's plane in the normal eye rotated temporally on near-viewing, as in normal subjects, while in the paretic eye it failed to do so. In patients with acquired superior oblique palsy, Listing's plane was already rotated temporally during far-viewing and failed to rotate any farther on near-viewing, whereas in patients with congenital superior oblique palsy Listing's plane in the paretic eye was oriented normally during far-viewing and failed to rotate any farther on near-viewing. CONCLUSIONS: These results suggest that the superior oblique muscle, at least in part, is responsible for the temporal rotation of Listing's plane that occurs in normal subjects on convergence.
Abstract: Meniere disease patients sometimes report vertiginous Meniere attacks after vestibular neurectomy that spares hearing. To determine why, the authors compared postsurgical semicircular canal function in nine patients with preserved hearing with that of a control group with no preservation of hearing. The three-dimensional head impulse test revealed residual posterior canal function in all patients with vertigo attacks (eight). The control patients had no residual canal function. Thus, residual vestibular function on the ipsilesional side may cause vertiginous Meniere attacks.
Abstract: We report four patients with the syndrome of cerebellar ataxia with bilateral vestibulopathy (CABV) and, using search coil oculography, we validate its characteristic clinical sign, namely impairment of the visually enhanced vestibulo-ocular reflex (VVOR) or doll's head reflex. In our four patients, CABV began in the sixth decade of life; they are still ambulant and self-caring 8-20 years after onset. The cause of CABV in our four patients is unknown. None has a family history of cerebellar or vestibular disease; spinocerebellar ataxia (SCA) 1, 2, 3, 6, 7 and Friedreich's ataxia were excluded by genetic testing. Three of the four have a sensory peripheral neuropathy but none has extrapyramidal or significant autonomic problems, and none has gluten sensitivity. We measured eye rotations in response to head-on-trunk head rotations and in response to head-and-trunk (en bloc) rotations. Horizontal smooth pursuit (SP), vestibulo-ocular reflex (VOR) and VVOR gains were measured in response to head rotations at 0.1, 0.3, 0.6 and 1.0 Hz. The optokinetic reflex (OKR) was tested by measuring optokinetic nystagmus slow phase velocity during constant 50 degrees /s rotation of the subject in light. The results showed that CABV patients had impairment of all three compensatory eye movement reflexes, the VOR, the OKR and SP. During VVOR testing, as the frequency of head rotation increased from 0.1 to 1.0 Hz, eye velocity failed to match head velocity, gaze velocity increased, and gaze position errors developed, which were corrected with bursts of saccades, the basis of the clinical sign of an impaired VVOR.
Abstract: Syringomyelia is an important cause of neurological deficit. Most cases of non-traumatic syringomyelia occur in association with a Chiari malformation. We present three unusual examples of syringomyelia with such an association. The first case is that of syringomyelia in a young woman with Marfan's syndrome, a spontaneous CSF leak and intractable intracranial hypotension. The second is a woman with long-standing lumbo-peritoneal shunt for pseudotumour cerebri who developed an acquired Chiari malformation. A young woman with a Dandy-Walker cyst that herniated into the upper cervical canal is the third case. These cases provide a basis for discussion of the pathogenesis and management of syringomyelia and the Chiari malformation in such cases.
Abstract: We describe changes in the extent of sway in a man with orthostatic tremor (OT) who reported increased stability after alcohol. He was tested at baseline and again after 40 g (0.5 g/kg) of alcohol. These results were compared to those of 3 age-matched controls (no alcohol). The patient's baseline sway was greater than controls, larger in the lateral than the anteroposterior plane, but retained normal responsiveness to the use of external support, increasing stance width, and vision. Tremor frequency significantly decreased after alcohol, as did low- and high-frequency tremor amplitude and the extent of body sway. Despite these findings, sway remained greater than controls. OT thus may show functionally important alcohol responsiveness.
Abstract: BACKGROUND: Of the more than 40 genetically defined dominantly inherited hearing loss syndromes, only a few are associated with bilateral vestibulopathy. No genetic mutations have been identified in families with bilateral vestibulopathy and normal hearing. OBJECTIVE: To perform a genome-wide scan for linkage in four families with dominantly inherited bilateral vestibulopathy. METHODS: Patients in four families reported brief episodes of vertigo followed by imbalance and oscillopsia. Bilateral vestibulopathy was documented with quantitative rotational testing. Most patients with bilateral vestibulopathy also had migraine. A 10 cM genome-wide screen was conducted using 423 microsatellite markers to identify linkage with vestibulopathy. RESULTS: The authors identified a 24 cM region on chromosome 6q suggestive of linkage to vestibulopathy in these four families (maximum lod score of 2.9 at marker D6S1556). A small fifth family with a different phenotype was not linked to this region on chromosome 6q. CONCLUSIONS: This is the first report of linkage in families with dominantly inherited vestibulopathy and normal hearing. Genetic heterogeneity is likely with inherited vestibulopathy.
Abstract: The clinical presentation of dural arteriovenous fistulae (DAVF) is dependent on their location and the nature of their venous drainage. The latter plays a critical part in determining whether or not the fistula gives rise to intracranial hypertension, which is present in only a minority of cases. We present a case of the pseudotumour cerebri syndrome in an elderly man with bilateral intracranial DAVF supplied by the occipital arteries. Cerebral angiography was required for definitive diagnosis, and to characterise the abnormal venous drainage. The pathophysiology of intracranial hypertension in DAVF is discussed.
Abstract: Vibration is an excitatory stimulus for both vestibular and proprioceptive afferents. Vibration applied either to the skull or to the neck muscles of subjects after unilateral vestibular deafferentation induces nystagmus and a shift of the subjective visual horizontal. Previous studies have ascribed these effects to vibratory stimulation of neck muscle proprioceptors. Using scleral search coils, we recorded three-dimensional eye movements during unilateral 92 Hz vibration of the mastoid bone or of the sternocleidomastoid (SCM) muscle in 18 subjects with chronic unilateral vestibular deficits after vestibular neurectomy or neuro-labyrinthitis. Nine subjects had lost function of all three semicircular canals (SSCs) on one side, and the other nine had lost function of only the anterior and lateral SSCs. Vibration of the mastoid bone or of the SCM muscle on either side induced an ipsilesional tonic shift of torsional eye position of up to 6.5 degrees during visual fixation, as well as a nystagmus with horizontal, vertical and torsional components in darkness. Subjects who had lost function of all three SSCs on one side showed a larger shift in ocular torsion in response to SCM vibration than did subjects who had lost function of only two SSCs. The difference between ocular torsion produced by ipsilesional muscle or bone vibration was not significantly different from that produced by contralesional bone or muscle vibration. The vibration-induced nystagmus rotation axis tended to align with the pitch (y) axis of the head in subjects who had lost only anterior and lateral SSC function, and with the roll (x) axis of the head in subjects who had lost function of all three SSCs. We propose that the previously described vibration-induced shift of the subjective visual horizontal can be explained by the vibration-induced ocular torsion, and that the magnitude of ocular torsion is related to the extent of the unilateral vestibular deficit. While altered proprioceptive inputs from neck muscles might be important in the mechanism of vibration-induced ocular torsion and nystagmus after unilateral vestibular deafferentation, vibratory stimulation of vestibular receptors in the intact labyrinth also appears to have an important role.
Abstract: OBJECT: Pseudotumor cerebri, or benign intracranial hypertension, is a condition of raised intracranial pressure in the absence of a mass lesion or cerebral edema. It is characterized by headache and visual deterioration that may culminate in blindness. Pseudotumor cerebri is caused by venous sinus obstruction in an unknown percentage of cases. The purpose of this study was to investigate the role of cerebral venous sinus disease in pseudotumor cerebri and the potential of endoluminal venous sinus stent placement as a new treatment. METHODS: Nine consecutive patients in whom diagnoses of pseudotumor cerebri had been made underwent examination with direct retrograde cerebral venography (DRCV) and manometry to characterize the morphological features and venous pressures in their cerebral venous sinuses. The cerebrospinal fluid (CSF) pressure was measured simultaneously in two patients. If patients had an amenable lesion they were treated using an endoluminal venous sinus stent. Five patients demonstrated morphological obstruction of the venous transverse sinuses (TSs). All lesions were associated with a distinct pressure gradient and raised proximal venous sinus pressures. Four patients underwent stent insertion in the venous sinuses and reported that their headaches improved immediately after the procedure and remained so at 6 months. Vision was improved in three patients, whereas it remained poor in one despite normalized CSF pressures. CONCLUSIONS: Patients with pseudotumor cerebri should be evaluated with DRCV and manometry because venous TS obstruction is probably more common than is currently appreciated. In patients with a lesion of the venous sinuses, treatment with an endoluminal venous sinus stent is a viable alternative for amenable lesions.
Abstract: The effects of unilateral vestibular deafferentation (UVD) on the linear vestibulo-ocular reflex (LVOR) were studied by measuring three-dimensional eye movements in seven UVD subjects evoked by impulsive eccentric roll rotation while viewing an earth-fixed target at 200, 300, or 600 mm and comparing their responses to 11 normal subjects. The stimulus, a whole-body roll of approximately 1 degrees, with the eye positioned 815 mm eccentric to the rotation axis, produced an inter-aural linear acceleration of approximately 0.5 g and a roll acceleration of approximately 360 degrees /s(2). The responses generated by the LVOR comprise horizontal eye rotations. Horizontal eye velocity at 100 ms from stimulus onset in UVD subjects was significantly lower than in normal subjects for all viewing distances, with no significant difference between ipsilesional and contralesional responses. LVOR acceleration gain, defined as the slope of actual horizontal eye velocity divided by the slope of ideal horizontal eye velocity during a 30-ms period starting 70 ms from stimulus onset, was bilaterally significantly reduced in UVD subjects at all viewing distances. Acceleration gain from all viewing distances was 1.04 +/- 0.28 in normal subjects, and in UVD subjects was 0.49 +/- 0.23 for ipsilesional and 0.63 +/- 0.27 for contralesional acceleration. LVOR enhancement in the first 100 ms by near viewing was still present in UVD subjects. LVOR latency in UVD subjects (approximately 39 ms) was not significantly different from normal subjects (approximately 36 ms). After UVD, LVOR is bilaterally and largely symmetrically reduced, but latency remains unchanged and modulation by viewing distance is still present.
Abstract: The authors studied eye movement responses to loud (110dB) clicks in 4 patients with Tullio effect due to superior semicircular canal dehiscence and in 9 normal subjects, by averaging the electro-oculogram. All 4 patients had small (0.1-0.3 deg) but easily reproducible vertical vestibulo-ocular reflex eye movement responses to the clicks. Normal subjects had responses that were at least 10 times smaller. The click-evoked vestibulo-ocular reflex test is a simple, robust way to screen dizzy patients for symptomatic superior semicircular dehiscence.
Abstract: We studied the compensatory eye movements made by subjects with unilateral vestibular deficits in response to passive (unpredictable, manually generated) and active (predictable, self-generated) head impulses. A typical head impulse is a brief, low-amplitude (15-20 degrees ), high-velocity (150-350 degrees /s), high-acceleration (4000-6000 degrees /s(2)), yaw head-on-trunk rotation. In the initial 75 ms of the response, the vestibulo-ocular reflex gain was significantly higher during active head impulses to both ipsilesional and contralesional sides, than during passive impulses. Mean gains were 0.15 (ipsilesional passive), 0.44 (ipsilesional active), 0.5 (contralesional passive), and 0.76 (contralesional active). Differences between active and passive head impulses were present from near the onset of head rotation. The mechanism for producing this behavior is unclear, but the findings could be related to enhanced sensitivity of second-order neurons during active head impulses. However, even with active movements, there is still a large and statistically significant asymmetry in the eye-movement responses for ipsilesional as opposed to contralesional head rotations. After 75 ms, rapid corrective eye movements often were generated to reduce any remaining gaze error.
Abstract: This is a report of a patient with an air-bone gap, thought 10 years ago to be a conductive hearing loss due to otosclerosis and treated with a stapedectomy. It now transpires that the patient actually had a conductive hearing gain due to superior semicircular canal dehiscence. In retrospect for as long as he could remember the patient had experienced cochlear hypersensitivity to bone-conducted sounds so that he could hear his own heart beat and joints move, as well as a tuning fork placed at his ankle. He also had vestibular hypersensitivity to air-conducted sounds with sound-induced eye movements (Tullio phenomenon), pressure-induced nystagmus and low-threshold, high-amplitude vestibular-evoked myogenic potentials. Furthermore some of his acoustic reflexes were preserved even after stapedectomy and two revisions. This case shows that if acoustic reflexes are preserved in a patient with an air-bone gap then the patient needs to be checked for sound- and pressure-induced nystagmus and needs to have vestibular-evoked myogenic potential testing. If there is sound- or pressure-induced nystagmus and if the vestibular-evoked myogenic potentials are also preserved, the problem is most likely in the floor of the middle fossa and not in the middle ear, and the patient needs a high-resolution spiral computed tomography (CT) of the temporal bones to show this.
Abstract: The aim of this study was to determine whether vergence-mediated changes in the axis of eye rotation in the human vestibulo-ocular reflex (VOR) would obey Listing's Law (normally associated with saccadic eye movements) independent of the initial eye position. We devised a paradigm for disassociating the saccadic velocity axis from eye position by presenting near and far targets that were centered with respect to one eye. We measured binocular 3-dimensional eye movements using search coils in ten normal subjects and 3-dimensional linear head acceleration using Optotrak in seven normal subjects. The stimuli consisted of passive, unpredictable, pitch head rotations with peak acceleration of approximately 2000 degrees /s(2 )and amplitude of approximately 20 degrees. During the pitch head rotation, each subject fixated straight ahead with one eye, whereas the other eye was adducted 4 degrees during far viewing (94 cm) and 25 degrees during near viewing (15 cm). Our data showed expected compensatory pitch rotations in both eyes, and a vergence-mediated horizontal rotation only in the adducting eye. In addition, during near viewing we observed torsional eye rotations not only in the adducting eye but also in the eye looking straight ahead. In the straight-ahead eye, the change in torsional eye velocity between near and far viewing, which began approximately 40 ms after the start of head rotation, was 10+/-6 degrees /s (mean +/- SD). This change in torsional eye velocity resulted in a 2.4+/-1.5 degrees axis tilt toward Listing's plane in that eye. In the adducting eye, the change in torsional eye velocity between near and far viewing was 16+/-6 degrees /s (mean +/- SD) and resulted in a 4.1+/-1.4 degrees axis tilt. The torsional eye velocities were conjugate and both eyes partially obeyed Listing's Law. The axis of eye rotation tilted in the direction of the line of sight by approximately one-third of the angle between the line of sight and a line orthogonal to Listing's plane. This tilt was higher than predicted by the one-quarter rule. The translational acceleration component of the pitch head rotation measured 0.5 g and may have contributed to the increased torsional component observed during near viewing. Our data show that vergence-mediated eye movements obey a VOR/Listing's Law compromise strategy independent of the initial eye position.
Abstract: OBJECTIVE: To examine the properties and potential clinical uses of myogenic potentials to bone conducted sound. METHODS: Myogenic potentials were recorded from normal volunteers, using bone conducted tone bursts of 7 ms duration and 250-2000 Hz frequencies delivered over the mastoid processes by a B 71 clinical bone vibrator. Biphasic positive-negative (p1n1) responses were recorded from both sternocleidomastoid (SCM) muscles using averaged unrectified EMG. The best location for stimulus delivery, optimum stimulus frequency, stimulus thresholds, and the effect of aging on evoked response amplitudes and thresholds were systematically examined. Subjects with specific lesions were studied. Vestibular evoked myogenic potentials (VEMP) to air conducted 0.1 ms clicks, 7 ms/250-2000 Hz tones, and forehead taps were measured for comparison. RESULTS: Bone conducted sound evoked short latency p1n1 responses in both SCM muscles. Ipsilateral responses occurred earlier and were usually larger. Mean (SD) p1 and n1 latencies were 13.6 (1.8) and 22.3 (1.2) ms ipsilaterally and 14.9 (2.1) and 23.7 (2.7) ms contralaterally. Stimuli of 250 Hz delivered over the mastoid process, posterosuperior to the external acoustic meatus, yielded the largest amplitude responses. Like VEMP in response to air conducted clicks and tones, p1n1 responses were absent ipsilaterally in subjects with selective vestibular neurectomy and preserved in those with severe sensorineural hearing loss. However, p1n1 responses were preserved in conductive hearing loss, whereas VEMP to air conducted sound were abolished or attenuated. Bone conducted response thresholds were 97.5 (3.9) dB SPL/30.5 dB HL, significantly lower than thresholds to air conducted clicks (131.7 (4.9) dB SPL/86.7 dB HL) and tones (114.0 (5.3) dB SPL/106 dB HL). CONCLUSIONS: Bone conducted sound evokes p1n1 responses (bone conducted VEMP) which are a useful measure of vestibular function, especially in the presence of conductive hearing loss. For a given perceptual intensity, bone conducted sound activates the vestibular apparatus more effectively than air conducted sound.
Abstract: BACKGROUND: Vibration to the head or neck excites vestibular and neck muscle spindle afferents. Can such vibrations improve the sensitivity of the subjective visual horizontal (SVH) test to chronic unilateral deficit of the vestibular system? DESIGN: Controlled experimental study. SETTING: Tertiary referral center. PATIENTS AND CONTROLS: Thirteen healthy subjects and 23 patients with chronic unilateral vestibular deficits after vestibular neurectomy or neurolabyrinthitis. Results of head-impulse test showed unilateral loss of function of all 3 semicircular canals in 14 patients and loss of anterior and lateral semicircular canals in 9 patients. INTERVENTION: Unilateral vibration (92 Hz; 0.6-mm amplitude) applied to sternocleidomastoid muscle (SCM) or mastoid bone. MAIN OUTCOME MEASURE: Results of SVH test (in degrees). RESULTS: Without vibration, 13 of 23 patients and all healthy subjects had SVH of less than 3 degrees (sensitivity, 43%; specificity, 100%). During vibration to the ipsilesional SCM, SVH increased to greater than 3 degrees in 21 of 23 patients but in only 1 of 13 healthy subjects (sensitivity, 91%; specificity, 92%). The patient group had significantly greater SVH shifts to the ipsilesional side than did healthy subjects in response to SCM and mastoid bone vibration on either side. The SVH shift during vibration to the ipsilesional SCM was significantly greater than that during vibration to the contralesional muscle (P<.001) or to the mastoid bone on either side (P<.05). The vibration-induced SVH shift was significantly greater in those patients with loss of 3 semicircular canals than in those with loss of 2 (P<.01). CONCLUSIONS: The sensitivity of the SVH test to chronic unilateral vestibular deficits can be improved by applying vibration to the SCM. The magnitude of vibratory SVH shift is related to the extent of unilateral deficit of the otolithic organs, vertical canals, or both.
Abstract: Sudden, spontaneous, unilateral loss of vestibular function without simultaneous hearing loss or brain stem signs is generally attributed to a viral infection involving the vestibular nerve and is called acute vestibular neuritis. The clinical hallmarks of acute vestibular neuritis are vertigo, spontaneous nystagmus, and unilateral loss of lateral semicircular function as shown by impulsive and caloric testing. In some patients with vestibular neuritis the process appears to involve only anterior and lateral semicircular function, and these patients are considered to have selective superior vestibular neuritis. Here we report on two patients with acute vertigo, normal lateral semicircular canal function as shown by both impulsive and caloric testing, but selective loss of posterior semicircular canal function as shown by impulsive testing and of saccular function as shown by vestibular evoked myogenic potential testing. We suggest that these patients had selective inferior vestibular neuritis and that contrary to conventional teaching, in a patient with acute spontaneous vertigo, unilateral loss of lateral semicircular canal function is not essential for a diagnosis of acute vestibular neuritis.
Abstract: A 53-year-old Caucasian woman with long-standing, well controlled, severe rheumatoid arthritis, treated with methotrexate, salazopyrin, naprosyn, prednisone and plaquenil, presented with progressive visual loss in each eye. She had a past history of non-necrotizing anterior scleritis that was treated with increased doses of prednisone. She developed left then right central scotomas, reduced vision and optic atrophy. Eventually a diagnosis of methotrexate-induced optic atrophy was made.
Abstract: A woman developed brain stem encephalopathy in association with serum anti-Ma2 antibodies and left upper lobe lung mass. T2 weighted MRI of the brain showed abnormalities involving the pons, left middle and superior cerebellar peduncles, and bilateral basal ganglia. Immunohistochemical analysis for serum antineuronal antibodies was confounded by the presence of a non-neuronal specific antinuclear antibody. Immunoblot studies showed the presence of anti-Ma2 antibodies. A premortem tissue diagnosis of the lung mass could not be established despite two CT guided needle biopsies, and the patient died as a result of rapid neurological deterioration. The necropsy showed that the lung lesion was an adenocarcinoma which expressed Ma2 immunoreactive protein. Neuropathological findings included prominent perivascular inflammatory infiltrates, glial nodules, and neuronophagia involving the brain stem, basal ganglia, hippocampus and the dentate nucleus of the cerebellum. Ma2 is an autoantigen previously identified in patients with germ cell tumours of the testis and paraneoplastic brain stem and limbic encephalitis. Our patient's clinical and immunopathological findings indicate that this disorder can affect women with lung adenocarcinoma, and that the encephalitic changes predominate in those regions of the brain known to express high concentrations of Ma proteins.
Abstract: In order to test the human angular vestibulo-ocular reflex in the dynamic range of normal head movements, we measured 3-dimensional compensatory eye-movement responses to low-amplitude (10-12 degrees), high-acceleration (3000-4000 degrees/s/s), passive, manually delivered head rotations (head "impulses") in the three planes of the semicircular canals in normal subjects, in subjects who had recovered from surgical unilateral vestibular deafferentation, and in patients after acute unilateral peripheral vestibulopathy, that is, from vestibular "neuritis." We found that canal-plane head impulses away from an intact semicircular canal, that is, toward a lesioned semicircular canal, invariably produce a vestibulo-ocular reflex with permanently low gain, typically less that 0.4 if the lesion is complete. These results are a necessary consequence of primary semicircular canal afferents being driven into inhibitory saturation by rapid angular accelerations. With practice, clinicians can learn to recognize the telltale compensatory saccades that patients with unilateral loss of semicircular canal function will make if asked to look at an earth-fixed target during head impulses in any one of the three semicircular canal planes.
Abstract: OBJECTIVE: To examine the concept of selective superior and inferior vestibular nerve involvement in vestibular neuritis by studying the distribution of semicircular canal (SCC) involvement in such patients. BACKGROUND: Vestibular neuritis was traditionally thought to involve the superior and inferior vestibular nerves. Recent work suggests that in some patients, only the superior nerve is involved. So far there are no reported cases of selective involvement of the inferior vestibular nerve. METHODS: The authors measured the vestibuloocular reflex from individual SCC at natural head accelerations using the head impulse test. The authors studied 33 patients with acute unilateral peripheral vestibulopathy, including 29 with classic vestibular neuritis and 4 with simultaneous ipsilateral hearing loss, 18 healthy subjects and 15 surgical unilateral vestibular deafferented patients. RESULTS: In patients with preserved hearing, eight had deficits in all three SCC, suggesting involvement of the superior and inferior vestibular nerves. Twenty-one had a lateral SCC deficit or a combined lateral and anterior SCC deficit consistent with selective involvement of the superior vestibular nerve. Two patients with ipsilateral hearing loss had normal caloric responses and an isolated posterior SCC deficit on impulsive testing. The authors propose that these two patients had a selective loss of inferior vestibular nerve function. CONCLUSION: Vestibular neuritis can affect the superior and inferior vestibular nerves together or can selectively affect the superior vestibular nerve.
Abstract: A patient with a postoperative fistula of the left posterior semicircular canal is presented. Negative pressure in the external ear canal produced upbeat-torsional nystagmus, which was recorded in three dimensions using binocular scleral search coils. The nystagmus was conjugate, without skew deviation, and its trajectory corresponded to the anatomic axis of the left posterior canal. The current study helps validate Ewald's first law in humans: the axis of nystagmus should match the anatomic axis of the semicircular canal that generated it. This law is clinically useful in diagnosing pathology of the vestibular end-organ, such as benign paroxysmal positional vertigo or the superior semicircular canal dehiscence syndrome.
Abstract: Anti-GQ1b antibodies are typically found in patients with the Miller Fisher syndrome, all of whom will have, by definition, acute ophthalmoplegia. The authors describe three patients with chronic ophthalmoplegia in the presence of persistently high titers of immunoglobulin G anti-GQ1b antibody detected in an ELISA, one of whom improved with immunotherapy. Anti-GQ1b antibodies may be associated with some cases of chronic ophthalmoplegia of unknown cause.
Abstract: Benign paroxysmal positional vertigo (BPPV) originating from the posterior semicircular canal (pSCC) is a common vestibular disorder that is easy to diagnose and usually easy to treat. The majority of patients with BPPV have no known inner ear disease; they have "primary" or "idiopathic" BPPV. However, a minority does have objective evidence of an inner ear disease on the same side as the BPPV and this group has "secondary" or "symptomatic" BPPV. Previous publications differ on the prevalence of secondary BPPV and about the types of inner ear diseases capable of causing it. In order to determine what proportion of patients have secondary as opposed to primary BPPV and which inner ear diseases are capable of causing secondary BPPV, we searched our database for the 10-year period from 1988 to 1997 and found a total of 2847 patients with BPPV. Of these, 81 (3%) had definite pSCC-BPPV secondary to an ipsilateral inner ear disease. Sixteen had Menière's disease, 24 had an acute unilateral peripheral vestibulopathy, 12 had a chronic unilateral peripheral vestibulopathy, 21 had chronic bilateral peripheral vestibulopathy and 8 had unilateral sensorineural hearing loss. It seems that any inner ear disease that detaches otoconia and yet does not totally destroy pSCC function can cause BPPV and that a case can be made for audiometry and caloric testing in all patients with BPPV.
Abstract: OBJECTIVES: To establish the role of high-resolution CT imaging and tests of vestibulocollic reflexes in diagnosing and understanding the pathogenesis of the Tullio phenomenon. BACKGROUND: The Tullio phenomenon is a syndrome in which acoustic stimulation produces symptoms and signs of vestibular activation. It has previously been associated with an abnormally low threshold for click-evoked vestibulocollic responses and also with dehiscence of the roof of the anterior (superior) semicircular canal on high-resolution CT scans of the temporal bones. METHODS: High-resolution CT scans of the temporal bones and vestibulocollic responses in sternocleidomastoid to both clicks and transmastoid galvanic stimulation (3 mA/2 msec) were studied in four patients with the Tullio phenomenon (one bilateral). RESULTS: Click-evoked thresholds were low for all affected ears (four at 65 dB nHL, one at 55 dB nHL) and normal (>70 dB nHL) for the three unaffected ears. In contrast, galvanic-evoked vestibulocollic responses were symmetric and of normal size in all patients. The bony roof of the anterior (superior) semicircular canal was thin, possibly absent, on CT of all affected ears and also in two out of three unaffected ears. CONCLUSIONS: The normal galvanic vestibulocollic responses indicate that sound sensitivity in patients with the Tullio phenomenon is likely to occur distal to the vestibular nerve, probably at the level of the receptors. Both click hypersensitivity and dehiscence of the anterior (superior) semicircular canal are associated with the Tullio phenomenon but as the CT scan abnormality can occur in clinically unaffected ears, click testing is important for specific diagnosis. Abnormal sound sensitivity, as demonstrated by click responses, confirms that the radiologic abnormality is function significant.
Abstract: We measured the guinea pig horizontal vestibulo-ocular reflex (hVOR) to high acceleration impulsive head rotations following a unilateral lateral semicircular canal (LSCC) occlusion. We found a significant hVOR deficit for rotations toward the side of the occluded LSCC and this deficit did not show systematic changes over 3 months. We considered the LSCC nerve was still functional as shown by the normal appearance of the crista of the LSCC ampulla and also electrical stimulation of the LSCC. We conclude that the VOR during angular acceleration in response to high acceleration shows no adaptive plasticity following a unilateral LSCC occlusion.
Abstract: We describe 4 patients who all simultaneously developed a sudden total or partial unilateral sensorineural hearing loss and an unusual acute peripheral vestibulopathy in the same ear characterized by posterior semicircular canal benign paroxysmal positional vertigo with intact lateral semicircular canal function. Two patients also had ipsilateral loss of otolith function. The vertigo resolved in all 4 patients after particle-repositioning maneuvers. The findings of audiometry and vestibular tests indicated that the lesion responsible for this syndrome was probably located within the labyrinth itself rather than within the vestibulocochlear nerve and that it was more likely a viral vestibulocochlear neurolabyrinthitis than a labyrinthine infarction.
Abstract: We studied the effects of 5 mA bilateral or unilateral, bipolar or monopolar, galvanic stimulation on the horizontal vestibulo-ocular reflex (hVOR) in six normal subjects during 0.01, 0.05, 0.1, 0.5 and 1 Hz yaw rotations and in two subjects during high-acceleration, low-amplitude yaw head rotations (head impulses). Bipolar galvanic stimulation induced horizontal nystagmus in all subjects and an asymmetry of the hVOR only during rotations below 0.1 Hz. Monopolar stimulation had no significant effect. The findings suggest that in humans galvanic stimulation affects those primary horizontal semicircular canal neurons that mediate the hVOR via indirect pathways through the velocity storage mechanism.
Abstract: HYPOTHESIS: The purpose of this study was to simulate an isolated directional preponderance (DP) on bithermal caloric testing by constructing a realistic neural network model. The simulation was designed to capture not only the characteristics of the nystagmus response to caloric stimulation but also the response to rotational stimulation in patients with an isolated caloric DP. BACKGROUND: The nature of an isolated DP--that is, a DP in the absence of a significant spontaneous nystagmus or canal paresis--is outlined in the preceding article. In this article, the authors investigate the possible neural basis for an isolated caloric DP using the mathematic modeling technique of neural network simulation. Neural network models are typically abstract in nature; however, in this case the network was based on the known structure and function of the central vestibular system. METHODS: The neural network model was based on the known neuroanatomy and neurophysiology of the horizontal vestibuloocular reflex pathway. A leftward-rightward asymmetric modification of the dynamic responses of simulated medial vestibular nucleus type IA neurons on one side, or of type 2 neurons on the other side, to peripheral input would generate an isolated caloric DP. RESULTS: The values of DP and associated canal paresis produced by the network were within the same range as in the patient group. The network also predicted that the rotational DP would be lower than the caloric DP: between 2.5% and 56.9% of the caloric DP value. The actual rotational DP value was between 3% and 57% (average 41%) of the corresponding caloric DP value. CONCLUSIONS: An isolated caloric DP can be simulated by a neural network model by modifying the activity of model units that represent medial vestibular nucleus neurons. An asymmetric dynamic response by a gain-enhancement function of either type 1A neurons on one side or of type 2 neurons on the other was sufficient to produce an isolated caloric DP. Excitatory gain enhancement of type 2 neurons produced a smaller rotational DP than a similar modification of type 1 neurons. This result indicates a potential neural locus for the generation of an isolated DP in patients with vestibular disorders.
Abstract: We measured the vestibulo-ocular reflex (VOR) during head impulses in a patient with right-sided internuclear ophthalmoplegia. Head impulses are rapid, passive, high-acceleration, low-amplitude head rotations in the direction of a particular semicircular canal (SCC). Adduction of the right eye was abnormally slow during right lateral SCC head impulses. The VOR during left posterior SCC impulses was severely deficient in both eyes, but the VOR during left anterior SCC impulses was only slightly deficient. We suggest that the vertical vestibulo-ocular pathways in humans are connected in SCC-plane coordinates, not the traditional roll and pitch coordinates, and that anterior SCC signals do not travel exclusively in the medial longitudinal fasciculus.
Abstract: To establish a link between otolith anatomy and function it is necessary to know the regions of the utricular and saccular maculae, which are stimulated by any arbitrary linear acceleration stimulus. That requires accurate information about the location and orientation of the spatially extended maculae in head-fixed coordinates and referred to head-fixed landmarks (such as Reid's line). New data showing the location of the otolithic maculae in the guinea pig with respect to head-fixed stereotaxic coordinates are presented. Guinea pigs were perfused with Karnovsky's fixative and the maculae were exposed while the head was held in a guinea pig stereotaxic device. An electrolytically sharpened fine wire held in a calibrated micromanipulator was touched to points all over the surface of each macula under visual observation with the aid of a high-power operating microscope. The x, y, z coordinates of these points were plotted using a three-dimensional plotting program. Both maculae have pronounced curvature so that dorsoventral shear forces will stimulate regions of both the utricular and saccular maculae.
Abstract: Vertical eye position-dependence of the human vestibuloocular reflex during passive and active yaw head rotations. The effect of vertical eye-in-head position on the compensatory eye rotation response to passive and active high acceleration yaw head rotations was examined in eight normal human subjects. The stimuli consisted of brief, low amplitude (15-25 degrees ), high acceleration (4,000-6,000 degrees /s2) yaw head rotations with respect to the trunk (peak velocity was 150-350 degrees /s). Eye and head rotations were recorded in three-dimensional space using the magnetic search coil technique. The input-output kinematics of the three-dimensional vestibuloocular reflex (VOR) were assessed by finding the difference between the inverted eye velocity vector and the head velocity vector (both referenced to a head-fixed coordinate system) as a time series. During passive head impulses, the head and eye velocity axes aligned well with each other for the first 47 ms after the onset of the stimulus, regardless of vertical eye-in-head position. After the initial 47-ms period, the degree of alignment of the eye and head velocity axes was modulated by vertical eye-in-head position. When fixation was on a target 20 degrees up, the eye and head velocity axes remained well aligned with each other. However, when fixation was on targets at 0 and 20 degrees down, the eye velocity axis tilted forward relative to the head velocity axis. During active head impulses, the axis tilt became apparent within 5 ms of the onset of the stimulus. When fixation was on a target at 0 degrees, the velocity axes remained well aligned with each other. When fixation was on a target 20 degrees up, the eye velocity axis tilted backward, when fixation was on a target 20 degrees down, the eye velocity axis tilted forward. The findings show that the VOR compensates very well for head motion in the early part of the response to unpredictable high acceleration stimuli-the eye position- dependence of the VOR does not become apparent until 47 ms after the onset of the stimulus. In contrast, the response to active high acceleration stimuli shows eye position-dependence from within 5 ms of the onset of the stimulus. A model using a VOR-Listing's law compromise strategy did not accurately predict the patterns observed in the data, raising questions about how the eye position-dependence of the VOR is generated. We suggest, in view of recent findings, that the phenomenon could arise due to the effects of fibromuscular pulleys on the functional pulling directions of the rectus muscles.
Abstract: To test a hypothesis about how otoliths resolve roll-tilts from translations, we measured human ocular torsion position [ocular counterrolling (OCR)] to maintained linear acceleration stimuli. All subjects (n = 8) were tested in two conditions where the same magnitude of shear along an interaural axis was generated in one of two ways: either by roll-tilt on a tilt-chair in a 1-g environment, or by centripetal linear acceleration during constant velocity rotation 1 m from the axis of rotation on a fixed-chair human centrifuge. The interaural shear to the otoliths was the same for these two conditions, but the dorsoventral shear was different and for all eight subjects the OCR on the centrifuge was significantly greater than the torsion on the tilt-chair, although the resultant angle was in fact smaller on the centrifuge than on the tilt-chair. The results confirm that dorsoventral shear is important for determining OCR. The otoliths may resolve potential stimulus ambiguities between tilts and translations by virtue of the different patterns of interaural and dorsoventral shear that these stimuli generate.
Abstract: OBJECTIVE: Complete unilateral loss of vestibular function results in a phase advance (reduced time constant) of the horizontal slow-phase nystagmus response to yaw-axis rotation. The objective of this study was to determine whether partial losses of lateral semicircular canal function would result in proportional reductions in the time constant. SETTING AND STUDY DESIGN: This was a retrospective study of consecutive patients' records at two tertiary referral centers for vestibular disorders. PATIENTS: Four hundred fifty-four patients who presented for evaluation of vertigo or imbalance or both and who were found to have partial or complete unilateral canal paresis on caloric testing. MAIN OUTCOME MEASURES: In 372 patients, the gain and time constant of the horizontal nystagmus response was measured using a 5-second velocity ramp of constant yaw-axis acceleration. Caloric responses to standard bithermal irrigations at 30 degrees and 44 degrees were obtained using an open-loop irrigation system. In a second group of 82 patients, the gain and time constant of the horizontal vestibulo-ocular reflex were measured using a sum-of-sines (pseudorandom) yaw-axis acceleration. The caloric response was measured using a closed-loop system. Results: In both groups, the peak gain of the nystagmus response was independent of the level of the canal paresis. However, the time constant of the response both toward and away from the lesioned side decreased proportionally with increasing canal paresis. CONCLUSION: This result supports the hypothesis that bilateral symmetrical peripheral vestibular input is a necessary condition for the mechanisms or processes underlying normal horizontal slow-phase velocity storage.
Abstract: We studied individual semicircular canal responses in three dimensions to high-acceleration head rotations ("head impulses") in subjects with known surgical lesions of the semicircular canals, and compared their results to those of normal subjects. We found that vestibular-ocular reflex (VOR) gains at close to peak head velocity in response to yaw, pitch and roll impulses were reliable indicators of semicircular canal function. When compared to normals, lateral canal function showed a 70-80% decrease in VOR gain at peak of yaw head velocity during ipsilesional yaw impulses. After the loss of one vertical canal function there was a 30-50% decrease in vertical and torsional VOR gain in response to ipsilesional pitch and roll impulses respectively. Bilateral deficits in anterior or posterior canal function resulted in a 80-90% decrease in vertical VOR gain during ipsilesional pitch impulses, while the loss of ipsilateral anterior and posterior canal functions will result in a 80-90% decrease in torsional VOR gain in response to ipsilesional roll impulses. Three-dimensional vector analysis and animation of the VOR responses in a unilateral vestibular deafferented subject to yaw, pitch and roll impulses further demonstrated the deficits in magnitude and direction of the VOR responses following the loss of unilateral lateral, anterior and posterior canal functions.
Abstract: The subjective visual horizontal and vestibular-evoked myogenic potentials are simple, robust, and reproducible tests of otolith dysfunction that can prove clinically useful diagnostic information in patients with vertigo and other balance disorders. While they appear to have high specificity for unilateral otolith dysfunction, further clinical research will be required to establish their sensitivity.
Abstract: We studied the human vestibulo-ocular reflex (VOR) in response to head 'impulses': brief, unpredictable, passive, high-acceleration (up to 4000 degrees/s2), low-amplitude (20-30 degrees) head rotations. We delivered the head impulses approximately in the plane of the semicircular canal (SCC) being tested. To test the anterior and posterior SCCs, the head impulses were delivered in a diagonal plane, midway between the frontal (roll) and sagittal (pitch) planes. We recorded head and eye position in three dimensions with scleral search coils in nine normal subjects, seven patients following unilateral surgical vestibular neurectomy and three patients following unilateral posterior SCC occlusion. In the post-surgical patients we demonstrated a severe, permanent VOR gain deficit (0.2-0.3) for head impulses directed toward any single non-functioning SCC. The sensitivity of the test depends on the physiological properties of primary vestibular afferents, and its specificity depends on the anatomical orientation of the SCCs. The diagonal head impulse is the first test of individual vertical SCC function in humans, and together with the horizontal head impulse, forms a comprehensive battery of SCC-plane tests. These canal-plane impulses could be useful in evaluating patients with vertigo or other vestibular disorders.
Abstract: We report on a patient who developed primary position upbeat nystagmus (ppUBN) due to a unilateral medial medullary infarction. On oculography, the slow phases of the nystagmus sometimes had an exponentially decreasing velocity waveform, indicating that the nystagmus was due to impairment of the vertical position-to-velocity neural integrator. On magnetic resonance imaging, the lesion was caudal to the vestibular nuclei and to the most rostral of the perihypoglossal nuclei, the nucleus intercalatus, a structure that was also involved in a previously reported case of ppUBN due to a unilateral medullary lesion. On the basis of these imaging and oculographic observations, we propose that a unilateral lesion of the nucleus intercalatus is sufficient to cause ppUBN and that the nucleus intercalatus is a part of the vertical position-to-velocity neural integrator in the human ocular-motor system.
Abstract: Systemic gentamicin can cause acute bilateral, simultaneous, symmetrical loss of vestibular function manifested by symptoms and signs of chronic vestibular insufficiency (ataxia and oscillopsia). We report 6 patients presenting with ataxia and oscillopsia, but without a history of vertigo, who had severe unilateral loss of vestibular function on caloric testing. The absence of vertigo in these patients could be explained by two possible mechanisms: either, the unilateral loss of vestibular function was subacute, occurring over several days so that compensation could occur, or bilateral vestibular loss occurred which was then followed by asymmetrical recovery of vestibular function. The second hypothesis is supported by the observation that vestibular hair cells can regenerate after aminoglycoside damage.
Abstract: We tested the hypothesis that the reason some patients compensate well after unilateral vestibular deafferentation (uVD) and others do not could be due to differences in eye-head coordination or in blink characteristics during natural, active head movements. Patients with well-compensated uVDs do not report distressing postural unsteadiness or an aversive sensation of apparent motion of a visual scene (oscillopsia) or "visual confusion" upon rapid head rotation as do those patients with poorly compensated uVDs. It has been suggested that well-compensated subjects eliminate the subjective sensations associated with retinal slip, which must occur as a result of an inadequate vestibuloocular reflex (VOR), either by restricting head movement to the lesioned side or by blinking during head turns. To test this, subjects stood at the curbside of a busy road with a 180 degrees view of regular, fast-moving traffic, which they scanned in preparation of crossing the road, and their eye and head movements and blinks were measured in this natural situation. Both normals and uVDs generated similar ranges of head position, head velocity and gaze magnitude, and all subjects performed a blink during the gaze saccade. Contrary to the hypothesis, no systematic differences were found between normals and either group of uVDs.
Abstract: This study was designed to measure ocular movements evoked by galvanic (DC) stimulation using computerised video-oculography. Long duration (>30 s) galvanic vestibular stimulation at currents of up to 5 mA through large-area surface electrodes over the mastoid processes causes maintained changes in the ocular torsional position of both eyes in healthy human subjects. With the subject seated and the head held firmly, torsion was measured by a computer-based image-processing system (VTM). Torsion was recorded in darkness, with or without a single fixation point. With bilateral stimulation, the upper poles of both eyes always torted away from the side of cathode placement and toward the anode. For unilateral stimulation, torsion was directed away from the cathode or toward the anode. The magnitude of ocular torsion was dependent on current strength: with bilateral stimulation the peak torsion was on average 2.88 degrees for 5-mA current intensity compared with 1.58 degrees for 3 mA. A smaller amplitude of torsion was obtained for unilateral stimulation. The average peak torsion was the same for both eyes for all forms of stimulation. Our findings indicate that low-intensity galvanic stimulation evokes ocular torsion in normal subjects, an effect which is consistent with an action on otolith afferents.
Abstract: Dual search coils were used to record horizontal, vertical and torsional eye movement components of one eye during nystagmus caused by off-center yaw rotation (yaw centrifugation). Both normal healthy human subjects (n=7) and patients with only one functioning labyrinth (n=12) were studied in order to clarify how the concomitant linear acceleration affected the nystagmus response. Each subject was seated with head erect on the arm of a fixed-chair human centrifuge, 1 m away from the center of the rotation, and positioned to be facing along a radius; either towards (facing-in) or away from (facing-out) the center of rotation. Both yaw right and yaw left angular accelerations of 10 degrees s(-2) from 0 to 200 degrees/s were studied. During rotation a centripetal linear acceleration (increasing from 0 to 1.24xg units) was directed along the subject's naso-occipital axis resulting in a shift of the resultant angle of the gravitoinertial acceleration (GIA) of 51 degrees in the subject's pitch plane and an increase in the total GIA magnitude from 1.0 to 1.59xg. In normal subjects during the angular acceleration off-center there were, in addition to the horizontal eye velocity components, torsional and vertical eye velocities present. The magnitude of these additional components, although small, was larger than observed during similar experiments with on-center angular acceleration (Haslwanter et al. 1996), and the change in these components is attributed to the additional effect of the linear acceleration stimulation. In the pitch plane the average size of the shift of the axis of eye velocity (AEV) during the acceleration was about 8 degrees for a 51 degrees shift of the GIA (around 16% of the GIA shift) so that the AEV-GIA alignment was inadequate. There was a very marked difference in the size of the AEV shift depending on whether the person was facing-in [AEV shift forward (i.e. non-compensatory) of about 4 degrees] or facing-out [AEV shift forward (i.e. compensatory) of around 12 degrees]. The linear acceleration decreased the time constant of decay of the horizontal component of the post-rotatory nystagmus: from an average of 24.8 degrees/s facing-in to an average of 11.3 degrees/s facing-out. The linear acceleration dumps torsional eye velocity in an manner analogous to, but independent of, the dumping of horizontal eye velocity. Patients with UVD had dramatically reduced torsional eye velocities for both facing-in and facing-out headings, and there was little if any shift of the AEV in UVD patients. The relatively small effects of linear acceleration on human canal-induced nystagmus found here confirms other recent studies in humans (Fetter et al. 1996) in contrast to evidence from monkeys and emphasizes the large and important differences between humans and monkeys in otolith-canal interaction. Our results confirm the vestibular control of the axis of eye velocity of humans is essentially head-referenced whereas in monkeys that control is essentially space-referenced.
Abstract: Three cases are reported of the pseudotumour cerebri syndrome-that is, intracranial hypertension without mass lesion or enlarged ventricles, due to cryptococcal meningitis. In these patients the papilloedema was successfully treated with optic nerve sheath decompression, and the intracranial hypertension with lumboperitoneal CSF shunting. These cases support the concept that pseudotumour cerebri is a syndrome of intracranial hypertension that can be due to any disorder producing obstruction of the CSF pathways at the level of the arachnoid villi. This concept is important because it directs therapy to normalise the intracranial pressure and preserve vision.
Abstract: We report on two patients each with tonic, contraversive partial ocular tilt reactions due to unilateral cerebellar lesions: one patient had had a caudal cerebellar hemorrhage, the other a posterior inferior cerebellar artery territory infarct. Both patients had tonic contraversive conjugate ocular torsion; one had skew deviation; neither had a head tilt. One patient had no specific neurologic deficit apart from the conjugate ocular torsion, which was first suspected because of a deviation of the subjective visual horizontal. These observations imply that the ocular tilt reaction (OTR), a brainstem otolith-ocular reflex of probable utricular origin, is under the inhibitory control of the ipsilateral caudal cerebellum, possibly the nodulus, and that a patient with a cerebellar infarct can present with imbalance as the only neurologic symptom and with conjugate ocular torsion as the only specific neurologic sign.
Abstract: We report the vestibular abnormalities in 5 patients with the CHARGE association (Coloboma, Heart disease, Atresia of choanae, Retarded growth and development and/or central nervous system anomalies, Genital hypoplasia, and Ear anomalies). All patients had absent vestibular function as indicated by absent vestibulo-ocular reflexes and severe imbalance on simultaneous deprivation of proprioception and vision, as well as delayed motor development. All 6 semicircular canals were aplastic in each of the patients. While cochlear function was severely reduced in 6 of the 10 ears, it was absent only in 3 ears and was actually intact below 3 kHz in 1 ear. All 10 bony cochleas were present on computed tomography, and although 7 appeared abnormal, 3 appeared normal. This study confirms that absence of the bony semicircular canals in the presence of a bony cochlea is a characteristic finding in CHARGE association. It also demonstrates that these disproportionate structural abnormalities are reflected in the functional abnormalities: absent vestibular function with preservation of some cochlear function.
Abstract: We recorded three-dimensional eye movements during angular acceleration steps from 0 to 250 degrees/s at 20 degrees/s2 about an earth-vertical axis. Experiments were performed on 27 normal subjects and on 19 patients who had recovered well from unilateral vestibular deafferentation on the right or left side. In addition to compensatory horizontal eye movements, significant vertical and torsional eye movement components were elicited. These vertical and torsional eye velocity traces led to a shift of the axis of eye velocity away from the axis of head velocity. Horizontal, vertical, and torsional velocity components showed clear differences between normals and patients with unilateral vestibular deafferentation. In normals, the axis of eye velocity tilted backward and slightly away from the axis of head velocity. Patients showed similar, but more pronounced, shifts during rotations toward the intact ear and shifts in the opposite direction for rotations toward the operated ear. Eye velocity traces were analyzed with special consideration given to the orientation of the axis of eye velocity. We speculate that the vertical and torsional velocity components may be due to the effects of Listing's plane, as well as the contributions of the otolith signals.
Abstract: To document the outcome of vestibular nerve section from the patient's point of view we reviewed 102 patients who had undergone vestibular nerve section 1 to 10 years after operation. Only 3 patients had experienced further vertigo attacks: 2 of these were cured by a further, this time translabyrinthine vestibular nerve section; 1 patient developed multiple sclerosis. In contrast, about 50% of patients developed some subjective problem with balance while standing or walking; in 15% it was present all the time and of moderate severity. Despite this, over 85% of patients reported that they felt much better or back to normal after the operation and were satisfied with the outcome. The development and application of objective preoperative measures of vestibular and, in particular, vestibulospinal function might improve patient selection for vestibular nerve section and thus reduce the number of dissatisfied patients.
Abstract: BACKGROUND: Benign paroxysmal positioning vertigo (BPPV) is generally thought to be caused by canalolithiasis in the posterior semicircular canal, an organ that is innervated by the inferior vestibular nerve. We hypothesized that absent vestibular evoked myogenic potentials (VEMPs) would indicate involvement of the inferior vestibular nerve and that posterior semicircular canal-type BPPV could not develop after vestibular neurolabyrinthitis (VNL) in patients with absent VEMPs. OBJECTIVE: To find out if VEMPs could be helpful in evaluating involvement of the inferior vestibular nerve in acute VNL. DESIGN: We reviewed the VEMP findings in 47 patients (34 men and 13 women) with acute VNL, 10 of whom had then developed posterior semicircular canal-type BPPV. RESULTS: While p13-n23, the first positive-negative peak of the VEMP, was ipsilaterally present on stimulation of the unaffected side in all patients, it was absent on the affected side in 16 patients (34%). The absence or presence of p13-n23 was independent of the results of caloric tests, pure tone audiometry, and auditory brain-stem responses. Typical posterior semicircular canal BPPV developed in 10 of the 47 patients after the acute attack of VNL, always on the same side as the neurolabyrinthitis. The p13-n23 potentials were preserved on stimulation of the affected ear in all 10 patients with BPPV. CONCLUSIONS: These results suggest that if VEMPs are absent from an ear that has suffered acute VNL, then posterior semicircular canal BPPV is unlikely to develop as a consequence of the VNL. The reason for this appears to be that the absence of VEMPs is due to involvement of the inferior vestibular nerve or involvement of the structures that it innervates.
Abstract: 1. The kinematics of the human angular vestibuloocular reflex (VOR) in three dimensions was investigated in 12 normal subjects during high-acceleration head rotations (head "impulses"). A head impulse is a passive, unpredictable, high-acceleration (3,000-4,000 degrees/s2) head rotation of approximately 10-20 degrees in roll, pitch, or yaw, delivered with the subject in the upright position and focusing on a fixation target. Head and eye rotations were measured with dual search coils and expressed as rotation vectors. The first of these two papers describes a vector analysis of the three-dimensional input-output kinematics of the VOR as two indexes in the time domain: magnitude and direction. 2. Magnitude is expressed as speed gain (G) and direction as misalignment angle (delta). G is defined as the ratio of eye velocity magnitude (eye speed) to head velocity magnitude (head speed). delta is defined as the instantaneous angle by which the eye rotation axis deviates from perfect alignment with the head rotation axis in three dimensions. When the eye rotation axis aligns perfectly with the head rotation axis and when eye velocity is in a direction opposite to head velocity, delta = 0. The orientation of misalignment between the head and the eye rotation axes is characterized by two spatial misalignment angles, which are the projections of delta onto two orthogonal coordinate planes that intersect at the head rotation axis. 3. Time series of G were calculated for head impulses in roll, pitch, and yaw. At 80 ms after the onset of an impulse (i.e., near peak head velocity), values of G were 0.72 +/- 0.07 (counterclockwise) and 0.75 +/- 0.07 (clockwise) for roll impulses, 0.97 +/- 0.05 (up) and 1.10 +/- 0.09 (down) for pitch impulses, and 0.95 +/- 0.06 (right) and 1.01 +/- 0.07 (left) for yaw impulses (mean +/- 95% confidence intervals). 4. The eye rotation axis was well aligned with head rotation axis during roll, pitch, and yaw impulses: delta remained almost constant at approximately 5-10 degrees, so that the spatial misalignment angles were < or = 5 degrees. delta was 9.6 +/- 3.1 (counterclockwise) and 9.0 +/- 2.6 (clockwise) for roll impulses, 5.7 +/- 1.6 (up) and 6.1 +/- 1.9 (down) for pitch impulses, and 6.2 +/- 2.2 (right) and 7.9 +/- 1.5 (left) for yaw impulses (mean +/- 95% confidence intervals). 5. VOR gain (gamma) is the product of G and cos(delta). Because delta is small in normal subjects, gamma is not significantly different from G. At 80 ms after the onset of an impulse, gamma was 0.70 +/- 0.08 (counterclockwise) and 0.74 +/- 0.07 (clockwise) for roll impulses, 0.97 +/- 0.05 (up) and 1.09 +/- 0.09 (down) for pitch impulses, and 0.94 +/- 0.06 (right) and 1.00 +/- 0.07 (left) for yaw impulses (mean +/- 95% confidence intervals). 6. VOR latencies, estimated with a latency shift method, were 10.3 +/- 1.9 (SD) ms for roll impulses, 7.6 +/- 2.8 (SD) ms for pitch impulses, and 7.5 +/- 2.9 (SD) ms for yaw impulses. 7. We conclude that the normal VOR produces eye rotations that are almost perfectly compensatory in direction as well as in speed, but only during yaw and pitch impulses. During roll impulses, eye rotations are well aligned in direction, but are approximately 30% slower in speed.
Abstract: 1. We studied the three-dimensional input-output human vestibuloocular reflex (VOR) kinematics after selective loss of semicircular canal (SCC) function either through total unilateral vestibular deafferentation (uVD) or through single posterior SCC occlusion (uPCO), and showed large deficits in magnitude and direction in response to high-acceleration head rotations (head "impulses"). 2. A head impulse is a passive, unpredictable, high-acceleration (3,000-4,000 degrees/s2) head rotation through an amplitude of 10-20 degrees in roll, pitch, or yaw. The subjects were tested while seated in the upright position and focusing on a fixation target. Head and eye rotations were measured with the use of dual search coils, and were expressed as rotation vectors. A three-dimensional vector analysis was performed on the input-output VOR kinematics after uVD, to produce two indexes in the time domain: magnitude and direction. Magnitude is expressed as speed gain (G) and direction as misalignment angle (delta). 3. G. after uVD, was significantly lower than normal in both directions of head rotation during roll, pitch, and yaw impulses, and were much lower during ipsilesional than during contralesional roll and yaw impulses. At 80 ms from the onset of an impulse (i.e., near peak head velocity), G was 0.23 +/- 0.08 (SE) (ipsilesional) and 0.56 +/- 0.08 (contralesional) for roll impulses, 0.61 +/- 0.09 (up) and 0.72 +/- 0.10 (down) for pitch impulses, and 0.36 +/- 0.06 (ipsilesional) and 0.76 +/- 0.09 (contralesional) for yaw impulses (mean +/- 95% confidence intervals). 4. delta, after uVD, was significantly different from normal during ipsilesional roll and yaw impulses and during pitch-up and pitch-down impulses. delta was normal during contralesional roll and yaw impulses. At 80 ms from the onset of the impulse, delta was 30.6 +/- 4.5 (ipsilesional) and 13.4 +/- 5.0 (contralesional) for roll impulses, 23.7 +/- 3.7 (up) and 31.6 +/- 4.4 (down) for pitch impulses, and 68.7 +/- 13.2 (ipsilesional) and 11.0 +/- 3.3 (contralesional) for yaw impulses (mean +/- 95% confidence intervals). 5. VOR gain (gamma), after uVD, were significantly lower than normal for both directions of roll, pitch, and yaw impulses and much lower during ipsilesional than during contralesional roll and yaw impulses. At 80 ms from the onset of the head impulse, the gamma was 0.22 +/- 0.08 (ipsilesional) and 0.54 +/- 0.09 (contralesional) for roll impulses, 0.55 +/- 0.09 (up) and 0.61 +/- 0.09 (down) for pitch impulses, and 0.14 +/- 0.10 (ipsilesional) and 0.74 +/- 0.06 (contralesional) for yaw impulses (mean +/- 95% confidence intervals). Because gamma is equal to [G*cos (delta)], it is significantly different from its corresponding G during ipsilesional roll and yaw, and during all pitch impulses, but not during contralesional roll and yaw impulses. 6. After uPCO, pitch-vertical gamma during pitch-up impulses was reduced to the same extent as after uVD; roll-torsional gamma during ipsilesional roll impulses was significantly lower than normal but significantly higher than after uVD. At 80 ms from the onset of the head impulse, gamma was 0.32 +/- 0.13 (ipsilesional) and 0.55 +/- 0.16 (contralesional) for roll impulses, 0.51 +/- 0.12 (up) and 0.91 +/- 0.14 (down) for pitch impulses, and 0.76 +/- 0.06 (ipsilesional) and 0.73 +/- 0.09 (contralesional) for yaw impulses (mean +/- 95% confidence intervals). 7. The eye rotation axis, after uVD, deviates in the yaw plane, away from the normal interaural axis, toward the nasooccipital axis, during all pitch impulses. After uPCO, the eye rotation axis deviates in same direction as after uVD during pitch-up impulses, but is well aligned with the head rotation axis during pitch-down impulses.
Abstract: A 64 year old woman with a predominantly midline pontine tegmental haemorrhage presented with bilateral total deafness. One week later reasonable pure-tone thresholds appeared but she still had total bilateral loss of speech discrimination. At that time contralateral acoustic reflexes were bilaterally absent, whereas ipsilateral acoustic reflexes and waves IV and V of the brainstem auditory evoked potential were bilaterally preserved. It is proposed that this patient's hearing deficit was due to inactivation of the ventral acoustic striae decussating in the trapezoid body. This case supports the contention that in humans the ventral pontine acoustic decussation carries most of the neural signals required for hearing and perhaps all the neural signals required for speech perception.
Abstract: Using dual torsion scleral search coils we have recorded 3-dimensional eye position during yaw angular accelerations of 20 degrees/s2 about an earth vertical axis in healthy subjects and in patients with unilateral vestibular deafferentation (UVD). These experiments produced two interesting results: i) even in healthy subjects, the axis of eye velocity did not coincide with the (earth vertical) stimulus axis during centred rotation; ii) Patients with UVD had torsional eye velocity components that were systematically different from those in normal subjects. While in normals the direction of the torsional component of the eye velocity depended on the direction of rotation and was on average approximately symmetric for CW and CCW yaw rotation, there was a clear asymmetry in patients, which was distinctly different for left and right UVD.
Abstract: We studied vestibular evoked myogenic potentials in 6 patients after unilateral vestibular neurectomy and in 22 patients after unilateral vestibular neuritis and unilateral absent caloric responses. We found that the ipsilesional vestibular evoked potentials were abolished in every patient after unilateral vestibular neurectomy. In vestibular neuritis patients we found that the ipsilesional vestibular evoked potentials were absent in some but not in all cases. These findings confirm that the p13-n23 potential is of vestibular origin and also show that it is not of lateral canal origin.
Abstract: Responses of single neurons in the vestibular nerve to high-intensity clicks were studied by extracellular recording in anaesthetised guinea pigs. One hundred and two neurons in the posterior division of the superior branch or in the inferior branch of the vestibular nerve were activated at short latency by intense clicks. The latency of activation was short (median 0.9 ms) and the threshold was high: the click intensity for evoking the response of these cells was around 60 dB above the auditory brainstem response threshold. Animals were tilted and rotated to identify physiologically the sensory region of the labyrinth from which the activated neurons originated. Seventeen neurons responded to static tilt as well as clicks. These results show that vestibular receptors, probably the otoliths, respond to clicks at intensities corresponding to those used in a new clinical test of the vestibulo-collic pathway.
Abstract: The responses to rapid, passive, unpredictable, low amplitude (10-20 degrees), high acceleration (3,000-4,000 degrees/s2) head rotations were used to study the human vestibulo-ocular reflex (VOR) in pitch and yaw plane after unilateral posterior semicircular canal occlusion (uPCO) in 10 subjects. The results from these 10 uPCO subjects were compared with those from 18 normal subjects. The VOR gains at a head velocity of 200 degrees/s in the uPCO subjects were: pitch upward = 0.62 +/- 0.06, pitch downward = 0.87 +/- 0.11, yew ipsilesion = 0.78 +/- 0.06, yaw contralesion = 0.79 +/- 0.10 and in normal subjects were: pitch upward = 0.92 +/- 0.06, pitch downward = 0.96 +/- 0.04, yaw right = 0.88 +/- 0.05, yaw left = 0.91 +/- 0.12 (group means +/- twotailed 95% confidence intervals). The results showed that the pitch-vVOR gain was significantly (p < 0.05) decreased in response to upward head impulses whereas in response to downward, ipsilesion and contralesion head impulses were not significantly different (p > 0.05) from the normals. This study shows that there is 30% permanent residual deficit of the upward pitch-vVOR with an up-down asymmetry in pitch-vVOR gain following inactivation of a single posterior semicircular canal and that compensation of pitch-vVOR function is incomplete.
Abstract: The vestibulo-ocular reflex (VOR) was studied in nine human subjects 2-15 months after permanent surgical occlusion of one posterior semicircular canal. The stimuli used were rapid, passive, unpredictable, low-amplitude (10-20 degrees), high-acceleration (3000-4000 degrees/s2) head rotations in pitch and yaw planes. The responses measured were vertical and horizontal eye rotations, and the results were compared with those from 19 normal subjects. After unilateral occlusion of the posterior semicircular canal, the gain of the head-up pitch vertical VOR--the vertical VOR generated by excitation from only one and disfacilitation from two vertical semicircular canals--was reduced to 0.61 +/- 0.06 (normal 0.92 +/- 0.06) at a head velocity of 200 degrees/s. In contrast the gain of the head-down pitch vertical VOR--the VOR still generated by excitation from two, but disfacilitation from only one vertical semicircular canal--was within normal limits: 0.86 +/- 0.11 (normal 0.96 +/- 0.04). The gain of the horizontal VOR in response to yaw head rotations--ipsilesion 0.81 +/- 0.06 (normal 0.88 +/- 0.05) and contralesion 0.80 +/- 0.11 (normal 0.92 +/- 0.11)--was within normal limits in both directions (group means +/- two-tailed 95% confidence intervals given in each case). These results show that occlusion of just one vertical semicircular canal produces a permanent deficit of about 30% in the vertical VOR gain in response to rapid pitch head rotations in the excitatory direction of the occluded canal. This observation indicates that, in response to a stimulus in the higher dynamic range, compensation of the human VOR for the loss of excitatory input from even one vertical semicircular canal is incomplete.
Abstract: Using an acute scleral search coil technique for measuring eye position in alert animals we have shown that after UVD the yaw VOR in the guinea pig shows a permanent gain asymmetry. There is a reduced gain during the first 100 ms of brief, high acceleration horizontal head rotations ("yaw head impulses") towards the operated side, but only a small loss in gain for similar rotations towards the intact side. This result confirms that the horizontal E response during the first 100 ms of an abrupt high acceleration head rotation is a clear indicator of the function of the horizontal canal. These results are similar to those in human patients after unilateral acoustic neuroma operations. The asymmetry in response is large shortly after UVD and decreases over time but is permanent.
Abstract: Vestibular sensory input is just one sensory input involved in the control of functions such as gaze and posture. The recovery of gaze and posture control after partial or complete unilateral loss of vestibular input is reviewed. The relatively rapid and apparently complete behavioral recovery after unilateral vestibular loss was once regarded as justifying vestibular compensation being used as a text-book example of plasticity in the CNS. This review emphasizes how false that impression is: Detailed examination shows that vestibular compensation is not a single process that recovers completely at a rapid rate but is made up of a number of subprocesses that recover to different levels and at different rates. In some subprocesses there is very modest recovery; in other subprocesses there is probably substitution of other sensory input for the affected vestibular input. It also seems that in some instances new behavioral strategies appear to be learned to allow gaze and posture control to operate as if normal. Recent evidence concerning the physiological and pharmacological mechanisms underlying vestibular compensation is reviewed.
Abstract: We investigated the use of skull taps with a modified clinical reflex hammer as a method of vestibular activation. Using recently described EMG techniques to measure vestibulocollic reflexes in response to clicks, we were able to show analogous short-latency potentials to taps. The earliest responses were invariably absent on the side of a previous vestibular nerve section but were preserved in profound sensorineural or conductive hearing loss. We propose that the taps activated the vestibular apparatus directly by a bone-conducted vibration wave.
Abstract: A patient was seen with secondary cluster headache whose acute pain responded promptly to sumatriptan. The headaches started after injury to the vertebral artery. This finding provides clinical affirmation of the existence of the trigeminal/cervical nuclear overlap that is central to this condition.
Abstract: In recent years, owing to significant technological developments and an increased number of investigators entering the field, there have been spectacular advances in our understanding of the basic anatomy and physiology of the vestibular system. Unfortunately, these advances in basic science are slow to impact the clinical management of patients. We have selected a few important advances in clinical neurotology that have impacted the diagnosis and treatment of patients with vestibular disorders. This material was originally presented at the "Mechanisms of Vestibular Function and Dysfunction" symposium of the 1994 Neural Control of Movement meeting in Waikoloa, Hawaii.
Abstract: Electromyograms (EMGs) were recorded from surface electrodes over the sternomastoid muscles and averaged in response to brief (0.1 ms) clicks played through headphones. In normal subjects, clicks 85 to 100 dB above our reference (45 dB SPL: close to perceptual threshold for normal subjects for such clicks) evoked reproducible changes in the averaged EMG beginning at a mean latency of 8.2 ms. The earliest potential change, a biphasic positive-negativity (p13-n23), occurred in all subjects and the response recorded from over the muscle on each side was predominantly generated by afferents originating from the ipsilateral ear. Later potentials (n34, p44), present in most but not all subjects, were generated bilaterally after unilateral ear stimulation. The amplitude of the averaged responses increased in direct proportion to the mean level of tonic muscle activation during the recording period. The p13-n23 response was abolished in patients who had undergone selective section of the vestibular nerve but was preserved in subjects with severe sensorineural hearing loss. It is proposed that the p13-n23 response is generated by activation of vestibular afferents, possibly those arising from the saccule, and transmitted via a rapidly conducting oligosynaptic pathway to anterior neck muscles. Conversely, the n34 and p44 potentials do not depend on the integrity of the vestibular nerve and probably originate from cochlear afferents.
Abstract: See-saw nystagmus is an uncommon but highly characteristic eye movement disorder comprising intorsion and elevation of one eye, with synchronous extorsion and depression of the other. It generally has a pendular waveform and is due to a midline, extrinsic, suprasellar mass lesion compressing or invading the brainstem bilaterally at the meso-diencephalic junction. This report deals with the clinical and MRI findings in three patients (and binocular three-dimensional quantitative oculographic findings in one patient) with a jerk waveform see-saw nystagmus due in each case to a unilateral meso-diencephalic lesion. In each patient the torsional component of the nystagmus fast phases rotated the upper poles of the eyes toward the side of the lesion. Jerk see-saw nystagmus can be clinically indistinguishable from pendular see-saw nystagmus and from the torsional-vertical nystagmus which occurs with medullary lesions. We propose that jerk see-saw nystagmus is due to unilateral inactivation of the torsional eye-velocity integrator, thought to be in the interstitial nucleus of Cajal, with sparing of the torsional fast-phase generator, thought to be in the adjacent rostral interstitial nucleus of the medial longitudinal fasciculus.
Abstract: Rapid, passive, unpredictable, low-amplitude (10-20 degrees), high-acceleration (3000-4000 degrees/s2) head rotations were used to study the vertical vestibulo-ocular reflex in the pitch plane (pitch-vVOR) after unilateral vestibular deafferentation. The results from 23 human subjects who had undergone therapeutic unilateral vestibular deafferentation were compared with those from 19 normals. All subjects were tested while seated in the upright position. Group means and two-tailed 95% confidence intervals are reported for the pitch-vVOR gains in normal and unilateral vestibular deafferented subjects. In normal subjects, at a head velocity of 125 degrees/s the pitch-vVOR gains were: upward 0.89 +/- 0.06, downward 0.91 +/- 0.04. At a head velocity of 200 degrees/s, the pitch-vVOR gains were: upward 0.92 +/- 0.06, downward 0.96 +/- 0.04. There was no significant up-down asymmetry. In the 15 unilateral vestibular deafferented subjects who were studied more than 1 year after unilateral vestibular deafferentation, the pitch-vVOR was significantly impaired. At a head velocity of 125 degrees/s, the pitch-vVOR gains were: upward 0.67 +/- 0.11, downward 0.63 +/- 0.07. At a head velocity of 200 degrees/s, the pitch-vVOR gains were: upward 0.67 +/- 0.07, downward 0.58 +/- 0.06. There was no significant up-down asymmetry. The pitch-vVOR gain in unilateral vestibular deafferented subjects was significantly lower (P < 0.05) than the pitch-vVOR gain in normal subjects at the same head velocities. These results show that total, permanent unilateral loss of vestibular function produces a permanent symmetrical 30% (approximately) decrease in pitch-vVOR gain. This pitch-vVOR deficit is still present more than 1 year after deafferentation despite retinal slip velocities greater than 30 degrees/s in response to head accelerations in the physiological range, indicating that compensation of pitch-vVOR function following unilateral vestibular deafferentation remains incomplete.
Abstract: We reviewed 36 patients with gentamicin vestibulotoxicity to determine its relationship to gentamicin dosage, serum gentamicin levels, and the development of gentamicin nephrotoxicity. Thirty of the patients had received intravenous or intramuscular gentamicin; six had received intraperitoneal gentamicin. Sixteen of the 30 patients treated with intramuscular or intravenous gentamicin had received less than the recommended maximum dose of 5 mg/kg/day for less than the recommended maximum period of 10 days. Nephrotoxicity as well as vestibulotoxicity developed in 16 of these 30 patients. Gentamicin vestibulotoxicity was not recognized before discharge from hospital in 32 of the 36 patients. We conclude that as far as the vestibular system is concerned there is no safe gentamicin dose and no safe serum gentamicin level, and there is an increased risk of vestibulotoxicity in patients in whom nephrotoxicity develops. Physicians who use gentamicin should become more aware of the clinical features of vestibulotoxicity because stopping gentamicin as soon as symptoms of vestibulotoxicity appear could prevent permanent impairment of vestibular function.
Abstract: Three new, simple, clinically applicable tests of vestibular function are described. The first is a test of the response of the lateral semicircular canals to high accelerations. The test can even be done at the bedside where it can reveal severe unilateral or bilateral loss of lateral canal function. The test can also be recorded in a laboratory where it might show a less severe deficit of lateral canal function. The second is a simple, laboratory test of utricular function which depends on a subject's ability to align a bar with the subjective visual vertical. Patients with acute unilateral peripheral vestibular lesions invariably set the bar toward the side of the lesion. The third is a laboratory test of saccular function relying on a click-evoked inhibitory vestibulo-collic reflex recorded in the ipsilateral sternomastoid muscle. It can be done with equipment used for auditory evoked potentials.
Abstract: We report 3 patients with autopsy-proven Creutzfeldt-Jakob disease who, early in their course, developed abnormal eye movements that included periodic alternating nystagmus and slow vertical saccades. These findings suggested involvement of the cerebellar nodulus and uvula, and the brainstem reticular formation, respectively. Cerebellar ataxia was also an early manifestation and, in 1 patient, a frontal lobe brain biopsy was normal at a time when ocular motor and cerebellar signs were conspicuous. As the disease progressed, all saccades and quick phases of nystagmus were lost, but periodic alternating gaze deviation persisted. At autopsy, 2 of the 3 patients had pronounced involvement of the cerebellum, especially of the midline structures. Creutzfeldt-Jakob disease should be considered in patients with subacute progressive neurological disease when cognitive changes are overshadowed by ocular motor findings or ataxia.
Abstract: Sudden complete loss of input from one labyrinth results in a massive change in behaviour. A vigorous horizontal ocular nystagmus occurs together with postural changes. These dramatic changes are short-lived and within about a week they have almost disappeared. This very rapid recovery has been the basis for the postulation that vestibular compensation is a textbook model for the study of neural plasticity in the central nervous system. Whilst the behavioural recovery is dramatic, quantitative testing reveals the loss and the permanent asymmetry of the system (Table 1). Recordings from single neurones show that many neurones in the ipsilesional VN are silenced by the unilateral loss, but as they start to fire again, so the spontaneous nystagmus declines. The major question which is still unanswered is the cause of the return of the firing of neurones in the ipsilesional VN. The answer may be found by studies of the neurochemistry of the VN using brain slice preparations. This review shows some of the errors which have been made by attempting to infer purely vestibular function from measurements of eye movements when other sources of ocular motor control may operate.
Abstract: Patients were tested 1 day before and 1 week after therapeutic unilateral vestibular neurectomy (UVN) on vestibular tests which are likely determined primarily by otolithic function. UVN causes a maintained ocular torsion: fundus photographs showed that both eyes of every patients were rolled such that the upper pole of both eyes was tonically deviated towards the operated side, and there is a corresponding change in the perceived gravitational horizontal: patients set a small bar of LEDs bar down on the same side as their operation. One week after UVN, patients showed an asymmetrical sensitivity to linear acceleration vectors directed along their interaural axis in comparison to their preoperative settings for the same stimuli.
Abstract: See-saw nystagmus is a unique torsional-vertical eye movement disorder with a characteristic appearance. It is a pendular nystagmus with two distinct components: a conjugate torsional component and a disjunctive vertical component. In those cases of see-saw nystagmus in which a focal lesion has been identified, the lesion is usually a bilateral, symmetric lesion located at the mesodiencephalic junction. We report an unusual case of see-saw nystagmus which was due to a strictly unilateral mesodiencephalic lesion. Furthermore, the see-saw nystagmus had, in this case, a jerk wave-form rather than the usual pendular wave-form, with the torsional component of the jerk see-saw nystagmus beating toward the side of the lesion. These observations have an impact upon the localizing and lateralizing significance of torsional nystagmus in general and of see-saw nystagmus in particular.
Abstract: To determine the relative contributions of ampullofugal (AF) and ampullopetal (AP) stimulation of the horizontal semicircular canal (HSCC) to the horizontal vestibulo-ocular reflex (HVOR), 12 patients were studied 1 year after total unilateral vestibular deafferentation (UVD). Compensatory eye movement responses to impulses of horizontal head rotation were studied using magnetic search coils. The head impulses were rapid (up to 3000 deg/sec/sec) passive, unpredictable, step displacements of horizontal angular head position with respect to the trunk. The results from these 12 patients were compared with results from 30 normal subjects. An HVOR deficit was found to each side. The HVOR in response to head impulses toward the deafferented side, a response generated exclusively by ampullofugal stimulation of the single functioning HSCC, was severely deficient with an average gain of 0.25; the HVOR in response to head impulses toward the intact side, a response generated exclusively by ampullopetal stimulation of the single functioning HSCC, was mildly but significantly deficient compared with normal subjects. These results show that rapid, unpredictable head movements, unlike slow, predictable head movements, do demonstrate the AP-AF HVOR asymmetry, which could be expected from consideration of the behavior of single vestibular afferent neurons, an asymmetry that is expressed by Ewald's 2nd Law.
Abstract: One index of otolith function is the so-called oculogravic "illusion" that during centrifugal stimulation a small luminous bar, fixed with respect to the observer, appears to be roll-tilted by the same amount that the observer feels to be roll-tilted. Many patients undergoing therapeutic unilateral vestibular nerve section show the illusion symmetrically for left and right roll-tilts prior to the operation, but at testing one week after vestibular nerve section show a large asymmetry: they perceive the illusion when the resultant force is directed toward their intact ear, but they perceive a much reduced illusion when the force is directed toward their operated ear. This roll-tilt perceptual response asymmetry appears similar to the asymmetrical horizontal semicircular canal vestibulo-ocular responses for symmetrical but opposite head accelerations that these same patients exhibit for values of head angular accelerations in the natural range (Ewald's second law), and the present paper suggests that a version of Ewald's second law may apply to the otolithic system: specifically, that there is a response asymmetry for linear accelerations. Anatomical and physiological evidence concerning such an otolithic asymmetry is reviewed.
Abstract: The normal horizontal vestibulo-ocular reflex (HVOR) is largely generated by simultaneous stimulation of the two horizontal semicircular canals (HSCCs). To determine the dynamics of the HVOR when it is generated by only one HSCC, compensatory eye movements in response to a novel vestibular stimulus were measured using magnetic search coils. The vestibular stimulus consisted of low-amplitude, high-acceleration, passive, unpredictable, horizontal rotations of the head with respect to the trunk. While these so called head "impuses" had amplitudes of only 15-20 degrees with peak velocities up to 250 deg/s, they had peak accelerations up to 3000 deg/s/s. Fourteen humans were studied in this way before and after therapeutic unilateral vestibular neurectomy; 10 were studied 1 week or 1 year afterwards; 4 were studied 1 week and 1 year afterwards. The results from these 14 patients were compared with the results from 30 normal control subjects and with the results from one subject with absent vestibular function following bilateral vestibular neurectomy. Compensatory eye rotation in normal subjects closely mirrored head rotation. In contrast there was no compensatory eye rotation in the first 170 ms after the onset of head rotation in the subject without vestibular function. Before unilateral vestibular neurectomy all the patients' eye movement responses were within the normal control range. One week after unilateral vestibular neurectomy however there was a asymmetrical bilateral HVOR deficit. The asymmetry was much more profound than has been shown in any previous studies. The HVOR generated in response to head impulses directed away from the intact side largely by ampullofugal disfacilitation from the single intact HSCC (ignoring for the moment the small contribution to the HVOR from stimulation of the vertical SCCs), was severely deficient with an average gain (eye velocity/head velocity) of 0.25 at 122.5 deg/sec head velocity (normal gain = 0.94 +/- 0.08). In contrast the HVOR generated in response to head impulses directed toward the intact side, largely by ampullopetal excitation from the single intact HSCC, was only mildly (but nonetheless significantly) deficient, with an average gain of 0.80 at 122.5 deg/sec head velocity. At these accelerations there was no significant improvement in the average HVOR velocity gain in either direction over the following year. These results indicate that ampullopetal excitation from one HSCC can, even in the absence of ampullofugal disfacilitation from the opposite HSCC, generate a near normal HVOR in response to high-acceleration stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
Abstract: Asymmetric vestibular function is the basis of vertigo. Whereas caloric tests can identify unilateral peripheral loss or impairment of horizontal semicircular canal function reasonably accurately, there is as yet no single accepted test of unilateral otolith hypofunction. In some advanced vestibular laboratories around the world, new and perhaps diagnostically useful tests of otolith function are being devised. The physiologic basis and the present clinical applications of these tests are reviewed.
Abstract: We studied 4 patients with tonic contraversive ocular tilt reactions due to unilateral, paramedian, mesodiencephalic lesions. This is in contrast to the only 2 previously reported patients with ocular tilt reactions due to unilateral mesodiencephalic lesions, each of whom had a paroxysmal ipsiversive ocular tilt reaction. This new finding is considered in the context of previous clinical and experimental data on the various types of ocular tilt reactions that follow stimulation or destruction of the peripheral and central vestibular system. Otolithic inputs to the interstitial nucleus of Cajal from the contralateral vestibular nucleus and motor outputs from the interstitial nucleus of Cajal to cervical and ocular motoneurons could be involved in the ocular tilt reaction. We propose that in patients with unilateral meso-diencephalic lesions, a tonic contraversive ocular tilt reaction could be due to persistently decreased resting activity of ipsilateral interstitial nucleus neurons, whereas a paroxysmal ipsiversive ocular tilt reaction could be due to transiently increased activity of the same interstitial nucleus neurons. Cases of ocular tilt reaction due to unilateral meso-diencephalic lesion point to the existence of a crossed graviceptive pathway between the vestibular nucleus and the contralateral interstitial nucleus of Cajal.
Abstract: The ability of 33 patients to perceive the direction, relative to the body long axis, of a linear acceleration vector acting in the coronal plane, roll-tilt perception, was studied at various times, before and from 1 week to 6 months after unilateral, selective vestibular neurectomy for Meniere's disease, acoustic neuroma or intractable paroxysmal vertigo. The results of these patients were compared with the results of 31 normal subjects and two control patients who had both vestibular nerves surgically sectioned. Rotating on a fixed-chair centrifuge in an otherwise darkened room, each observer was required to indicate his perception of the direction of the resultant gravito-inertial vector by setting a small, motor-driven, illuminated bar, attached to the chair but rotatable in the fronto-parallel plane, to the perceived gravitational horizontal. Normal subjects accurately align the bar with respect to the gravito-inertial resultant vector which, in the dark, they assume to be the gravitational vertical. This percept has been called the oculogravic illusion. Accurate roll-tilt perception is due to vestibular (probably mainly otolithic) sensory information since patients with bilateral vestibular neurectomies do not perceive the resultant vector accurately. Whereas normal subjects perceive resultant vectors directed to the right and to the left equally accurately, roll-tilt perception was invariably asymmetrical one week after unilateral vestibular neurectomy. Even at rest there was an asymmetry in the baseline settings, so that patients set the bar down on the side of the operated ear, in order for it to appear gravitationally horizontal: if a patient had a right vestibular nerve section then he set the bar clockwise (from the patient's view) below the true gravitational horizontal. With increasing gravito-inertial resultant angles there was an increasing asymmetry of roll-tilt perception due both to decreased sensitivity to roll-tilt stimuli directed towards the operated ear and to transiently increased sensitivity to roll-tilt stimuli directed towards the intact ear. A progressive decrease in both perceptual asymmetries followed, rapidly in the first 3 weeks, more slowly in the next 6 months.(ABSTRACT TRUNCATED AT 400 WORDS)
Abstract: A new model of otolithic stimulation by linear acceleration is presented and compared to previous models, based upon anatomical evidence and on the ability of normal subjects to sense the direction of a linear acceleration vector acting in the coronal plane (roll-tilt perception). There are two basic methods of generating roll-tilt stimuli: 1) tilt-chairs either inside or outside a centrifuge and 2) fixed-chair centrifuges. The present model is based on consideration of the probable otoconial displacement produced by these two different methods of stimulation and the model incorporates a major role for the elastic restoring force of the otolith membrane. When this force is taken into account, and most previous models have ignored it, the model predicts that different patterns of otoconial displacement will be produced in tilt-chair and in fixed-chair centrifuge experiments. The different roll-tilt perception produced by these two methods may be caused by the different otoconial displacement patterns. It is suggested that the elastic restoring force of the otoconial membrane may contribute to space motion sickness.
Abstract: Two patients presented with painful unilateral oculomotor nerve palsies without evidence of ocular congestion or hypoxia. They were initially thought to have posterior communicating or distal internal carotid aneurysms, but had, in fact, dural-cavernous sinus shunts, draining posteriorly into the inferior petrosal sinus. One patient later developed a moderately severe congestive ophthalmopathy, and repeated selective carotid arteriograms showed that the shunt was now draining anteriorly into the superior ophthalmic vein. In the other patient, the oculomotor nerve palsy resolved without the development of any further signs. These observations support the concept that dural-cavernous sinus shunts produce symptoms that are dependent on the direction of drainage from the shunt. It is clear that the direction of drainage can change and that thrombosis of the posterior cavernous sinus determines the direction of drainage. The exact mechanism of the cranial neuropathy is, however, unknown.
Abstract: We examined six patients who developed blurring or oscillopsia as a result of downbeat nystagmus while being treated with lithium carbonate. Of these six plus six previously described similar patients, all but two developed downbeat nystagmus insidiously as an isolated disorder in the setting of otherwise satisfactory therapeutic control, without clinical or biochemical evidence of acute lithium intoxication. Only six of these 12 patients were able either to reduce or to stop taking lithium, and in only two of these six did the downbeat nystagmus improve or remit.
Abstract: Unilateral loss of horizontal semicircular canal function, termed canal paresis, is an important finding in dizzy patients. To our knowledge, apart from head-shaking nystagmus, no clinical sign of canal paresis has yet been described and the term derives from the characteristic finding on caloric tests: little or no nystagmus evoked by either hot or cold irrigation of the affected ear. We describe a simple and reliable clinical sign of total unilateral loss of horizontal semicircular canal function: one large or several small oppositely directed, compensatory, refixation saccades elicited by rapid horizontal head rotation toward the lesioned side. Using magnetic search coils to measure head and eye movement, we have validated this sign in 12 patients who had undergone unilateral vestibular neurectomy.
Abstract: Four patients with partial epileptic seizures for several years, but without permanent neurological deficits, were found to have giant aneurysms of the middle cerebral artery. None had a history of subarachnoid hemorrhage. Operative findings included compression of the medial temporal and subfrontal cortex, infarction of the superior temporal gyrus, and evidence of previous hemorrhage from the aneurysms. In two patients, clipping of the aneurysm with decompression of the adjacent temporal lobe cured the seizure disorder. In the other two patients, the aneurysms could only be wrapped, and the seizures continued. It is postulated that focal compression of temporal lobe structures and local hemodynamic phenomena caused by the giant aneurysm predispose to epilepsy in these patients.
Abstract: We describe two patients with paraneoplastic cerebellar syndromes who gained clinically useful neurologic remissions following radical excision of the primary cancer. In both patients the syndrome was characterized by the rapid onset of gait ataxia, nausea, postural vertigo, central positional nystagmus, and saccadic oscillations. These observations encourage radical treatment of the primary cancer in patients with advanced malignant neoplasms who are disabled by cerebellar dysfunction, and lend support to a current hypothesis that paraneoplastic cerebellar degeneration is due to anticerebellar Purkinje cell antibodies elaborated by the primary cancer.
Abstract: Conventional neuro-otological tests measure only semi-circular canal function and not otolith function. A clinically acceptable test of otolith function was developed. Previous studies suggested that muscle responses which occur less than 100 ms after release into free-fall are part of a startle reflex originating in the otoliths. With a couch capable of producing sudden, safe, comfortable free-falls it was shown that in normal subjects orbicularis oculi muscle responses (that is eyeblinks) invariably began within 45 ms of this stimulus and confirmed that these eyeblink reflexes are part of a generalised startle reflex, as they cross-habituate with eyeblink reflexes elicited by supraorbital nerve stimulation. Eyeblink reflexes to free-fall may prove a useful clinical test of otolith function.
Abstract: We reviewed the clinical and oculomotor findings in 62 patients with downbeating nystagmus (DBN). Only those patients whose DBN was enhanced in lateral gaze were included. Apart from gait ataxia, few patients had additional neurologic signs. The two most common causes of DBN were cerebellar ectopia (25%) and cerebellar degeneration (25%) with another 10% having a variety of conditions. In about 40% the cause remained undiagnosed. In some patients with idiopathic DBN and in others with DBN due to cerebellar ectopia, the disease progressed slowly, if at all. In DBN the slow-phase velocity is dependent on vertical head position and head velocity in pitch; vertical pursuit, particularly downward pursuit, is defective and vertical vestibulo-ocular reflexes are intact. We concluded that at least some cases of DBN were due to an imbalance in otolithocular reflexes. The lesion causing DBN appears to be in the vestibulocerebellum, perhaps the nodulus, a structure that normally inhibits otolith-ocular reflexes.
Abstract: Computerized tomography revealed a thrombosed giant intracavernous carotid aneurysm in a man who presented with ophthalmoplegia and headache. Angiography confirmed complete aneurysmal thrombosis and also revealed complete occlusion of the ipsilateral internal carotid artery. Aneurysmotomy and thrombectomy produced substantial reduction in mass effect, with symptomatic improvement. The spontaneous thrombosis of giant intracranial aneurysms is discussed.
Abstract: Resting and postural tremor, intention and action tremor, clonus and the cogwheel phenomenon in Parkinson's disease have been characterised in terms of frequency content using spectral analysis. Typical resting tremor ranged in peak frequency from 4 to 5.3 HZ with tremor in each individual varying only by 0.2 to 0.3 HZ. The peak frequency of postural tremor ranged between 6 and 6.2 HZ. Intention tremor appeared to be an exaggeration of postural tremor. Clonus evoked by active or passive stretch at the wrist had a frequency of 6 HZ and appeared to be a continuation of postural tremor. The cogwheel phenomenon was found at frequencies between 6 and 6.5 HZ and between 7.5 to 9 HZ. Action tremor was indistinguishable from the cogwheel phenomenon. Some patients had either a symptomatic resting tremor with a concurrent 6 HZ component of smaller amplitude or a symptomatic postural tremor with a 4-5 HZ component of smaller amplitude. These combinations would produce two peaks in the power spectrum. When this occurred EMG studies showed that individual muscles had two types of rhythmical activation suggesting that the tremors have separate mechanisms. Likewise some patients had a symptomatic 6 HZ tremor on posture with a second peak at 8-10 HZ in the physiological band. Therefore, the 6 HZ postural tremor is not an exaggeration of physiological tremor. On the basis of wave form and frequency similarities postural tremor, the low frequency type of active or passive cogwheeling, intention tremor and clonus possibly involve a common spinal mechanism. Higher frequency cogwheel phenomenon and action tremor may be an exaggeration of physiological tremor. More than 80% of patients with Parkinson's disease manifest tremors at both 4-5 HZ and 6 HZ. This combination would appear to be the strongest objective criterion for the diagnosis of basal ganglia disease.
Abstract: Two patients with longstanding acquired periodic alternating nystagmus (PAN) were treated with baclofen, 30 mg/day. Baclofen abolished the PAN and relieved oscillopsia in both patients but was ineffective in another patient with congenital PAN.
Abstract: We studied reversed optokinetic nystagmus (OKN) in 31 patients and found that it is actually the patient's own gaze-modulated spontaneous nystagmus shifted to the primary position of gaze by optokinetic stimulation. Two of our 31 patients were known to have congenital nystagmus. Most of the 29 others were adults who presented with neurological symptoms and nystagmus and were therefore suspected of having posterior fossa lesions. However, their nystagmographic findings and benign natural history suggest that they also had congenital nystagmus, which was unrecognized until they developed incidental neurological symptoms. These cases support the view that reversed OKN is pathognomonic of a benign, probably congenital, nystagmus.
Abstract: A case is described of a subependymal giant-cell astrocytoma that occurred as a mural nodule within a cyst in the parietal lobe. The tumor recurred twice over a period of 47 years despite two extensive surgical resections. Neither the patient nor any of his children suffered tuberous sclerosis, a disease with which this type of astrocytoma is associated.
Abstract: A case of acute glomerulonephritis occurring during Staphylococcus albus infection of a ventriculoatrial shunt is described. It is the first case in which renal biopsy was repeated after clinical cure by shunt removal. This indicates that isolated haematuria and some histopathological changes may persist for at least a year.
Abstract: Visual suppression of vestibulo-ocular reflexes (induced vestibular nystagmus) differs between normal subjects and patients with various neurological disorders. Abnormalities of VOR suppression were associated consistently with abnormalities of the visual and/or vesitibular oculomotor reflexes and in particular with abnormal smooth pursuit eye movements in the direction of abnormal suppression. Absent VOR suppression in a gaze position of, and in the same direction as, a spontaneous nystagmus was found exclusively in patients with spontaneous nystagmus of central nervous system origin. Conversely, ability to suppress in these circumstances was found only in patients with spontaneous nystagmus of peripheral labyrinthine origin. Suppression of VOR was abnormal ipsilaterally in patients with unilateral cerebral hemisphere lesions and abnormal in both the horizontal and vertical planes in patients with basal ganglia lesions. Failure of VOR suppression in the absence of spontaneous nystagmus indicates a supratentorial lesion.
Abstract: Following inadvertent destruction of the left vestibular labyrinth during stapedectomy, a patient developed a transient abnormality of posture consisting of leftward ocular counterrolling, leftward had tilting, and a right-over-left skew deviation. This postural pattern, known as the "ocular tilt reaction," is the normal compensatory response of the dependent utricle to tilting. In this patient, the unopposed action of the intact right utricle was presumably responsible for the appearance of a normal leftward ocular tilt reaction.
Abstract: Abnormal head movements have been studied in a variety of diseases using objective recording techniques and the data analysed with respect to the frequency content of the movement. Flopping, nodding, tic, chorea, myoclonic jerks, and most head tremors involve frequencies of approximately 2 and 4 Hz which correspond to the natural fundamental and second harmonic resonances of the head as determined by the mechanical properties of the head/neck system. These findings provide a basis for classification of abnormal head movements as well as an explanation of the characteristics of those arising from hypotonia of the neck muscles. The similarities between tremor frequencies and natural resonances suggest that in the case of the head, tremor arises from disorders of neural mechanisms normally responsible for the fine control of voluntary head movement and for stabilisation of the head during disturbance of posture. Head movements in cases of congenital nystagmus were found to be of two types. Some were of bizarre waveform, in no way assisted vision, and were taken to be of primarily pathological origin and classified as tremors. Others were learned adaptive responses which assisted vision either by interrupting the nystagmus, as in the case of spasmus nutans, or by compensating for the nystagmus with an inverse waveform and were called nodding. A prerequisite for true compensatory nodding is modified vestibulo-ocular reflex.
Abstract: We report four patients with paralysis of downward gaze but with intact upward gaze, including one with detailed clinico-pathological studies and another with a focal computerized axial tomographic (CT) scan abnormality confirming the presence of bilateral lesions of the dorsomedial red nucleus, including the fasciculus retroflexus. It is suggested that sudden, permanent selective failure of downward gaze accompanied by transient disturbance of consciousness is an embolic syndrome of the posterior thalamosubthalamic or rubral artery.
Abstract: Head shaking and congenital nystagmus were recorded in a patient presented with visual tasks. When she was at rest the nystagmus took a 6 cycles per second saw-tooth wave-form. When she was attentive the nystagmus beat at a 2 to 2.6 cycles per second with a saddle-shaped deformation which permitted foveation. The head shaking occurred occasionally when the patient was attentive and was phase-locked to the nystagmus with resemblances in wave form and direction. Deceleration of the head shaking to zero velocity and peak displacement (to the left) coincided with the onset of the saddle of the nystagmus and hence assisted foveation; all other parts of the head-shaking cycle were detrimental to vision. It is proposed that the head shaking has a common pathological origin with the nystagmus and that, just as an isolated congenital nystagmus wave form becomes altered with attention to permit periods of foveal fixation, the pattern of combined head and eye nodding in this patient provided similar peroids of fixation.
Abstract: A patient with congenital hydrocephalus and poor vision since early childhood, but with normal motor and intellectual development, suffered progressive mental deterioration during the last decade of life. At necropsy he was found to have severe hydrocephalus secondary to a lipoma of the midbrain tectum obstructing the aqueduct of Sylvius. In addition, the septum pellucidum was absent, the corpus callosum was thinned, and the anterior visual system was atrophic. The case emphasizes the importance of full neuroradiological investigation of congenital hydrocephalus. The possible association of intracranial lipoma with septo-optic dysplasia is discussed.
