Tapping the head activates the vestibular system: a new use for the clinical reflex hammer.

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.

Posterior semicircular canal nystagmus is conjugate and its axis is parallel to that of the canal.

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.

Absent vestibular evoked myogenic potentials in vestibular neurolabyrinthitis. An indicator of inferior vestibular nerve involvement?

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.

Sudden unilateral hearing loss with simultaneous ipsilateral posterior semicircular canal benign paroxysmal positional vertigo: a variant of vestibulo-cochlear neurolabyrinthitis?

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.

Head impulses reveal loss of individual semicircular canal function.

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.

Intratympanic gentamicin in Ménière's disease: results of therapy.

To define better the benefits and risks of intratympanic gentamicin injection treatment of intractable vertigo or drop attacks due to Ménière's disease, we reviewed the charts of 18 patients whom we have now observed for > 1 year after having completed this mode of therapy. There were nine women and nine men aged 29-81 years; all had poor hearing in the affected ear. Of the 18 patients, 14 have had no further vertigo or drop attacks (11 patients after a single set of three to five injections, another three after a further set of one to five injections). The treatment could be effective even if it did not abolish caloric responses from the treated ear, even if it did not produce an acute vestibular deafferentation syndrome afterwards, and even after a failed vestibular nerve section. After treatment, five of the 18 patients developed oscillopsia and ataxia--symptoms and signs of (presumably permanent) chronic vestibular insufficiency; this proportion is not obviously lower than that after vestibular neurectomy or surgical labyrinthectomy. Of the 18 patients, 12 showed no change in the 1-kHz threshold and 13 showed no change in the 4-kHz threshold. When hearing did deteriorate, the threshold rose by more than 30 dB at 1 kHz in four patients and at 4 kHz in six patients. We conclude and confirm that intratympanic gentamicin injections are a convenient and, in most cases, effective and safe treatment for intractable vertigo or drop attacks due to Ménière's disease.

Three-dimensional vector analysis of the human vestibuloocular reflex in response to high-acceleration head rotations. I. Responses in normal subjects.

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.

Three-dimensional vector analysis of the human vestibuloocular reflex in response to high-acceleration head rotations. II. responses in subjects with unilateral vestibular loss and selective semicircular canal occlusion.

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.

Compensation of the human vertical vestibulo-ocular reflex following occlusion of one vertical semicircular canal is incomplete.

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.

The effect of unilateral posterior semicircular canal inactivation on the human vestibulo-ocular reflex.

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.

Unilateral vestibular deafferentation causes permanent impairment of the human vertical vestibulo-ocular reflex in the pitch plane.

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.

The click-evoked vestibulo-ocular reflex in superior semicircular canal dehiscence.

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.