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.
Expedited Publication
A dehiscence in the bony superior semicircular canal permits sound and pressure to activate vestibular receptors to produce vestibular symptoms such as imbalance, vertigo and oscillopsia,1 and auditory symptoms such as conductive hyperacusis, autophony, and pulsatile tinnitus.2-4⇓⇓
The diagnosis of symptomatic superior semicircular canal dehiscence (SCD) is made by finding SCD on CT in a patient with sound and pressure induced nystagmus (the Tullio effect).1,5⇓ Ancillary findings are an audiometric air-bone gap, preserved acoustic reflexes2,4,5⇓⇓ and low-threshold, high-amplitude vestibular evoked myogenic potentials.2,4-6⇓⇓⇓
There are problems with detecting sound and pressure induced nystagmus. Clinical examination requires special test equipment (Frenzel glasses, audiometer and pneumatic otoscope) and produces both false positives and negatives, and it can be missed with electronystagmography since it is usually a low-velocity, torsional-vertical nystagmus that is suppressed by vision.
Loud sounds produce vertical eye movements detectible with electro-oculography7 in some patients with the Tullio effect as well as short latency activation of neck muscles in pigeons with experimental bony superior semicircular canal fistulas.8 Seeking a simple way to screen patients for sound-induced vestibular activation we wondered if loud clicks of the type that evoke a lowered threshold vestibulo-collic reflex (i.e., the vestibular evoked myogenic potential) in patients with SCD2-4,6⇓⇓⇓ would reliably evoke a vestibulo-ocular reflex (VOR) that could be detected by averaging the electro-oculogram.
Patients.
Four patients with sound or pressure-induced vestibular symptoms or both from one ear with a SCD were studied; two had an asymptomatic contralateral SCD. All had experienced hyperacusis, imbalance, and oscillopsia provoked by effort or loud sound for years.
Patient 1, a 46-year-old man, had noted imbalance, pulse-synchronous tinnitus, and oscillopsia after exercising for 3 years. His own voice sounded too loud in his right ear and if he shouted he would feel off balance. On examination there was no spontaneous, head-shaking, gaze-evoked, or positional nystagmus, no VOR deficiency on impulsive testing, and no abnormality of stance or gait. Video nystagmoscopy in darkness revealed that both a nasal Valsalva maneuver and a 2kHz, 110dB NHL (relative to Normal Hearing Level) tone in the right ear, but not in the left, would produce a low-velocity nystagmus that beat downwards and clockwise (from the patient’s point of view). Raising or lowering external ear canal pressure with an ear syringe produced no nystagmus or eye movements from either side. A three-dimensional search-coil recording showed that the rotation axis of the sound-induced nystagmus was nearly orthogonal to the plane of the right superior semicircular canal (figure 1A, 1B). The Weber test lateralized to the right, the Rinne test showed that bone conduction was better than air conduction bilaterally and the patient could hear a 256 Hz tuning fork placed at his ankle. The audiogram on the right showed bone-conduction thresholds of −5dB, from 0.25 to 2 kHz, with air-bone gaps of 5–20 dB but intact acoustic reflexes. Air-conduction thresholds were the same on the left as on the right but there was no air-bone gap. Vestibular evoked myogenic potentials with 110 dB click stimuli showed normal amplitude ipsilateral p13-n23 responses of 225 μV from the right ear and 64 μV from the left; the threshold was reduced to 65 dB in the right ear but was 100 dB (normal >90 dB) in the left.2,3,4,6⇓⇓⇓ During this test, the patient noted oscillopsia with each click in the right ear. A 0.5 mm slice thickness spiral CT of the temporal bones showed bilateral SCD (figure 2).
Figure 1. Sound-induced nystagmus. Three-dimensional scleral search recordings from the left eye in response to 110 db, 2 kHz pure-tones in the right ear of Patient 1 (A) and of Patient 2 (C). The dotted line (0°) shows the primary position of the eye. Patient 1 responds with a nystagmus that has counterclockwise torsional, upward vertical and rightward horizontal slow phases. Patient 2 has no nystagmus response to the sound. The peak velocity of each nystagmus slow phase from Patient 1, when plotted as a vector, aligns close to the rotation axis of the right superior semicircular canal (B). Semicircular canal rotation axes: LS = left superior, LP = left posterior, LL = left lateral, RS = right superior, RP = right posterior RL = right lateral. Head axes: X = roll, Y = pitch, Z = yaw.
Figure 2. Superior semicircular canal dehiscence. Reconstructed high-resolution spiral CT of the bony labyrinth from patients 1 and 2 showing the superior semicircular canal dehiscence (SCD) in the symptomatic (right) ear. The reconstruction (top left) is in the plane of the superior semicircular canal. A CT from a normal subject is shown for comparison (top right). Patient 2, who had only pressure and not sound-induced nystagmus, had a larger SCD (bottom right) than Patient 1 (bottom left). In humans the superior semicircular canal radius is about 8 mm. A = anterior; P = posterior, M = head of the malleus; CC = crus communis of superior and posterior semicircular canals; TM = tympanic membrane; MC = mandibular condyle. (CT scans courtesy of Dr. John Harding-Smith, Central Sydney, Imaging.)
Patient 2, a 65-year-old man, presented with imbalance triggered by sneezing. For years he had found the sound of his own chewing too loud and had noted that he could hear his own joints move. Infra-red videonystagmoscopy revealed that a nasal Valsalva maneuver, as well as raised external ear canal pressure in the right ear, but not in the left, produced slight counterclockwise ocular torsion, whereas lowered pressure produced slight clockwise torsion. Neither a 0.5 kHz nor a 2 kHz 110 dB NHL tone produced nystagmus from either ear (see figure 1C). The audiogram showed a severe high-frequency, noise-induced hearing loss as well as bilateral low-frequency air-bone gaps with 0.5 kHz bone thresholds of 0 dB NHL on the left and −10 dB on the right. Vestibular evoked myogenic potential amplitudes in response to 110 dB clicks were 307 μV from the right ear (N<250 μV) and 115 μV from the left. The threshold was 80 dB in the right ear (N>90 dB) and 100 dB in the left. A 0.5 mm slice thickness spiral CT of the temporal bones showed a 5–6 mm SCD bilaterally (see figure 2).
Click-evoked VOR measurement.
The patient was supine and watched a target 80 cm straight ahead. Using left eye vertical and binocular horizontal electro-oculography, eye movements were calibrated with 1 degree up, down, left and right saccades. As in the vestibular evoked myogenic potential test the stimuli were monaural 100 μsec clicks, 128 at 5/sec, from 110 dB to 60 dB NHL in 10 dB steps.
Click-evoked VOR results.
In 9 normal subjects with no balance or hearing problems the click-evoked VOR was either undetectable or had a amplitude of less than 0.025 deg at a threshold of 110 dB.
In Patient 1 the initial response to a 110 dB click in the right ear was an upward and apparently rightward eye movement with an onset latency of 7.5 msec. It had a vertical amplitude of about 0.3 deg and was followed immediately by a similar downward and leftward eye movement (figure 3); the response threshold was 70 dB, a value only 5 dB above the vestibular evoked myogenic potential threshold from the same ear. In response to a 110 dB click in the asymptomatic left ear, the click-evoked VOR was about 30 times smaller, 0.01 deg vertically, a value in the normal range.
Figure 3. Click-evoked vestibulo-ocular reflex. The responses from the symptomatic (right) ear of patients 1 and 2. The onset latency of the click-evoked vestibulo-ocular reflex (VOR) is about 7.5 msec. The initial response is upward as would be expected from activation of the superior semicircular canal. The click-evoked VOR threshold is about 70 dB in Patient 1 and 80 dB in Patient 2.
In Patient 2 the click-evoked VOR from the right ear had a threshold of 80 dB and amplitude of 0.13 deg at 110 dB (see figure 3). From the asymptomatic left ear the threshold was 110 dB and the amplitude was less than 0.01 deg, a value in the normal range.
In the 2 other patients, the click-evoked VOR threshold was 80–90 dB, the amplitude at 110 dB was 0.10–0.25 deg and the mean onset latency was 8.0 msec, a value identical in each patient to the onset latency of their vestibular evoked myogenic potential.
Discussion.
In response to a loud click 4/4 patients with symptomatic SCD had a small (0.1–0.3 deg), short latency, (about 8 msec to onset) VOR. The click-evoked VOR threshold is 70–80 dB, and the amplitude is 10 to 30 times larger than in normal subjects and in ears with asymptomatic SCD.
The click-evoked VOR has an onset latency (about 8 msec) that is similar to that of the horizontal VOR in response to rapid, passive yaw head rotations9 and to the click-evoked vestibulo-collic reflex, i.e., the vestibular evoked myogenic potential.10 The click-evoked VOR almost certainly has a torsional component, but this is not resolved in the vertical electro-oculogram. The click-evoked VOR could come from excitation of the dehiscent superior semicircular canal, or of the saccule, the source of the vestibular evoked myogenic potential, another click-evoked vestibular reflex with similar latency and threshold. Further studies of the three-dimensional properties of the click-evoked VOR in humans with natural SCD, and in animals with surgical SCD will be required to clarify this point.
The click-evoked VOR could be useful to screen dizzy patients for SCD and to decide which side is producing the symptoms in patients with known bilateral SCD, particularly in those who have only pressure, but not sound-induced nystagmus or ocular torsion1,4⇓ such as Patient 2 here.
Acknowledgments
Supported by the National Health and Medical Research Council of Australia, the Garnett Passe and Rodney Williams Memorial Foundation, the Ramaciotti Foundations and the RPA Hospital Neurology Department Trustees.
- Received November 19, 2002.
- Accepted January 24, 2003.
Letters: Rapid online correspondence
REQUIREMENTS
If you are uploading a letter concerning an article:
You must have updated your disclosures within six months: http://submit.neurology.org
Your co-authors must send a completed Publishing Agreement Form to Neurology Staff (not necessary for the lead/corresponding author as the form below will suffice) before you upload your comment.
If you are responding to a comment that was written about an article you originally authored:
You (and co-authors) do not need to fill out forms or check disclosures as author forms are still valid
and apply to letter.
Submission specifications:
- Submissions must be < 200 words with < 5 references. Reference 1 must be the article on which you are commenting.
- Submissions should not have more than 5 authors. (Exception: original author replies can include all original authors of the article)
- Submit only on articles published within 6 months of issue date.
- Do not be redundant. Read any comments already posted on the article prior to submission.
- Submitted comments are subject to editing and editor review prior to posting.
You May Also be Interested in
Hemiplegic Migraine Associated With PRRT2 Variations A Clinical and Genetic Study
Dr. Robert Shapiro and Dr. Amynah Pradhan