Reducing Sound Exposure During Ocular Vestibular Evoked Myogenic Potential Testing for Superior Semicircular Canal Dehiscence Syndrome.

BACKGROUND: Ocular vestibular evoked myogenic potentials (oVEMP) testing in response to air-conducted sound (ACS) has excellent sensitivity and specificity for superior semicircular canal dehiscence syndrome (SCDS). However, patients with SCDS may experience vertigo with the test, and recent works recommend minimizing acoustic energy during VEMP testing. PURPOSE: To develop an oVEMP protocol that reduces discomfort and increases safety without compromising reliability. METHODS: Subjects: Fifteen patients diagnosed with SCDS based on clinical presentation, audiometry, standard VEMP testing, and computed tomography (CT) imaging. There were 17 SCDS-affected ears and 13 unaffected ears. In nine (53%) of the SCDS-affected ears surgical repair was indicated, and SCD was confirmed in each. oVEMPs were recorded in response to ACS using 500 Hz tone bursts or clicks. oVEMP amplitudes evoked by 100 stimuli (standard protocol) were compared with experimental protocols with only 40 or 20 stimuli. RESULTS: In all three protocols, oVEMP amplitudes in SCDS-affected ears were significantly higher than in the unaffected ears (p < 0.001). 500 Hz tone bursts evoked oVEMPs with excellent (>90%) sensitivity and specificity in each of the three protocols. However, in the unaffected ears, lowering to 20 stimuli reduced the detection of oVEMP responses in some ears. Following surgical repair, oVEMPs normalized in each of the protocols. CONCLUSION: In oVEMP testing using ACS for SCDS, reducing the number of trials from 100 to 40 stimuli results in a more tolerable and theoretically safer test without compromising its effectiveness for the diagnosis of SCDS. Reducing to 20 stimuli may degrade specificity with clicks.

Upbeat nystagmus after bilateral superior canal plugging: A peripheral cause of vertical nystagmus.

Vertical nystagmus without a torsional component is generally considered a finding indicative of central nervous system pathology. We report two cases of purely upbeat nystagmus elicited with mastoid vibration after bilateral superior canal plugging, to highlight the vestibular pathophysiology involved in this unusual peripheral cause for upbeat nystagmus. Laryngoscope, 127:1698-1700, 2017.

The effect of increased intracranial pressure on vestibular evoked myogenic potentials in superior canal dehiscence syndrome.

OBJECTIVE: To determine if vestibular evoked myogenic potential (VEMP) responses change during inversion in patients with superior canal dehiscence syndrome (SCDS) compared to controls. METHODS: Sixteen subjects with SCDS (mean: 43, range 30-57 years) and 15 age-matched, healthy subjects (mean: 41, range 22-57 years) completed cervical VEMP (cVEMP) in response to air conduction click stimuli and ocular VEMP (oVEMP) in response to air conduction 500 Hz tone burst stimuli and midline tap stimulation. All VEMP testing was completed in semi-recumbent and inverted conditions. RESULTS: SCDS ears demonstrated significantly larger oVEMP peak-to-peak amplitudes in comparison to normal ears in semi-recumbency. While corrected cVEMP peak-to-peak amplitudes were larger in SCDS ears; this did not reach significance in our sample. Overall, there was not a differential change in o- or cVEMP amplitude with inversion between SCDS and normal subjects. CONCLUSIONS: Postural-induced changes in o- and cVEMP responses were measured in the steady state regardless of whether the labyrinth was intact or dehiscent. SIGNIFICANCE: VEMP responses are blunted during inversion. Although steady-state measurements of VEMPs during inversion do not increase diagnostic accuracy for SCDS, the findings suggest that inversion may provide more general insights into the equilibration of pressures between intracranial and intralabyrinthine fluids.

Air-conducted oVEMPs provide the best separation between intact and superior canal dehiscent labyrinths.

OBJECTIVE: First, to define the best single-step suprathreshold screening test for superior canal dehiscence syndrome (SCDS); second, to obtain further insight into the relative sensitivity of vestibular afferents to sound vibration in the presence of a superior canal dehiscence. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Eleven patients with surgically confirmed SCDS (mean, 50 yr; range, 32-66 yr) and 11 age-matched, healthy subjects (right ear only) with no hearing or vestibular deficits (mean, 50 yr; range, 33-66 yr). INTERVENTION: All subjects completed ocular and cervical vestibular evoked myogenic potential (o- and cVEMP) testing in response to air conduction (click and 500 Hz tone burst) and midline bone conduction (reflex hammer and Mini-shaker) stimulation. MAIN OUTCOME MEASURES: OVEMP n10 amplitude and cVEMP corrected peak-to-peak amplitude. RESULTS: OVEMP n10 amplitudes were significantly higher in SCDS when compared with healthy controls in response to all stimuli with the exception of reflex hammer. Likewise, cVEMP-corrected peak-to-peak amplitudes were significantly higher in SCDS when compared with healthy controls for air conduction stimulation (click and 500 Hz toneburst). However, there were no significant differences between groups for midline taps (reflex hammer or mini-shaker). Receiver operating characteristic curves demonstrated that oVEMPs in response to air conduction stimulation provided the best separation between SCDS and healthy controls. CONCLUSION: OVEMPs in response to air conduction stimulation (click and 500 Hz toneburst) provide the best separation between SCDS and healthy controls and are therefore the best single-step screening test for SCDS.

Ocular versus cervical VEMPs in the diagnosis of superior semicircular canal dehiscence syndrome.

OBJECTIVES: To determine whether cervical vestibular evoked myogenic potential (cVEMP) thresholds or ocular VEMP (oVEMP) amplitudes are more sensitive and specific in the diagnosis of superior semicircular canal dehiscence syndrome (SCDS). STUDY DESIGN: Prospective case-control study. SETTING: Tertiary referral center. SUBJECTS AND METHODS: Twenty-nine patients with SCDS (mean age 48 yr; range, 31-66 yr) and 25 age-matched controls (mean age 48 yr; range, 30-66 yr). INTERVENTION(S): cVEMP and oVEMP in response to air-conducted sound. All patients underwent surgery for repair of SCDS. MAIN OUTCOME MEASURE(S): cVEMP thresholds; oVEMP n10 and peak-to-peak amplitudes. RESULTS: cVEMP threshold results showed sensitivity and specificity ranging from 80% to 100% for the diagnosis of SCDS. In contrast, oVEMP amplitudes demonstrated sensitivity and specificity greater than 90%. CONCLUSION: oVEMP amplitudes are superior to cVEMP thresholds in the diagnosis of SCDS.

Ataxia telangiectasia: a "disease model" to understand the cerebellar control of vestibular reflexes.

Experimental animal models have suggested that the modulation of the amplitude and direction of vestibular reflexes are important functions of the vestibulocerebellum and contribute to the control of gaze and balance. These critical vestibular functions have been infrequently quantified in human cerebellar disease. In 13 subjects with ataxia telangiectasia (A-T), a disease associated with profound cerebellar cortical degeneration, we found abnormalities of several key vestibular reflexes. The vestibuloocular reflex (VOR) was measured by eye movement responses to changes in head rotation. The vestibulocollic reflex (VCR) was assessed with cervical vestibular-evoked myogenic potentials (cVEMPs), in which auditory clicks led to electromyographic activity of the sternocleidomastoid muscle. The VOR gain (eye velocity/head velocity) was increased in all subjects with A-T. An increase of the VCR, paralleling that of the VOR, was indirectly suggested by an increase in cVEMP amplitude. In A-T subjects, alignment of the axis of eye rotation was not with that of head rotation. Subjects with A-T thus manifested VOR cross-coupling, abnormal eye movements directed along axes orthogonal to that of head rotation. Degeneration of the Purkinje neurons in the vestibulocerebellum probably underlie these deficits. This study offers insights into how the vestibulocerebellum functions in healthy humans. It may also be of value to the design of treatment trials as a surrogate biomarker of cerebellar function that does not require controlling for motivation or occult changes in motor strategy on the part of experimental subjects.

Test-retest reliability and age-related characteristics of the ocular and cervical vestibular evoked myogenic potential tests.

OBJECTIVE: To determine the test-retest reliability and age-related trends of the cervical and ocular vestibular evoked myogenic potential (cVEMP and oVEMP, respectively) responses to air-conducted sound and bone-conducted vibration stimulation. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Fifty-three healthy adults with no hearing or vestibular deficits. INTERVENTION(S): All subjects underwent cVEMP and oVEMP testing in response to sounds (0.1-ms clicks and 500-Hz tone bursts) and vibration (midline forehead taps at the hairline, Fz, with a reflex hammer and a Brüel & Kjaer Mini-Shaker Type 4810). Twelve subjects underwent an additional testing session that was conducted at a mean of 10 weeks after the first one. MAIN OUTCOME MEASURE(S): Test-retest reliability for VEMP response parameters (latency, peak-to-peak amplitude, and asymmetry ratio) were assessed using the intraclass correlation coefficient (ICC). RESULTS: : oVEMP amplitudes had excellent test-retest reliability (ICC > 0.75) for all 4 stimuli; cVEMP amplitudes had excellent reliability for hammer taps and fair-to-good reliability for other stimuli. oVEMP asymmetry ratios had excellent reliability for clicks and fair-to-good reliability (ICC = 0.4-0.75) for other stimuli; cVEMP asymmetry ratios had fair-to-good reliability for clicks and hammer taps. Older subjects (>50 years old) were found to have significantly decreased cVEMP amplitudes in response to clicks, tones, and taps with a Mini-Shaker and significantly decreased oVEMP amplitudes in response to clicks, tones, and taps with a reflex hammer. No age-related changes were found for latencies or asymmetry ratios. CONCLUSION: Overall, oVEMP response parameters demonstrated better test-retest reliability than cVEMP response parameters, but oVEMPs and cVEMPs had similar age-related changes.

The human sound-evoked vestibulo-ocular reflex and its electromyographic correlate.

OBJECTIVE: Sound and vibration evoke a short-latency eye movement or "sound-evoked vestibulo-ocular reflex" (VOR) and an infraorbital surface potential: the "ocular vestibular-evoked myogenic potential" (OVEMP). We examined their relationship by measuring the modulation of both responses by gaze and stimulus parameters. METHODS: In seven subjects with superior semicircular-canal dehiscence (SCD) and six controls, the sound-evoked VOR was measured in 3D using scleral search coils. OVEMPs were recorded simultaneously, using surface electromyography. RESULTS: Eye movement onset (11.6+/-0.8ms) coincided with the OVEMP peak (12.1+/-0.35ms). OVEMP and VOR magnitudes were 5-15 times larger in SCD compared with controls. OVEMP amplitudes were maximal on upgaze and abolished on downgaze; VOR magnitudes were unaffected. When stimulus type was changed from sound to vibration, OVEMP and VOR changed concordantly: increasing in controls and decreasing in SCD. OVEMP and VOR tuned to identical stimulus frequencies. OVEMP and VOR magnitudes on upgaze were significantly correlated (R=0.83-0.97). CONCLUSION: Selective decrease of the OVEMP upon downgaze is consistent with relaxation or retraction of the inferior oblique muscles. The temporal relationship of OVEMP and VOR and their identical modulation by external factors confirms a common origin. SIGNIFICANCE: Sound-evoked OVEMP and VOR represent the electrical and mechanical correlates of the same vestibulo-ocular response.

Vestibular-evoked myogenic potential thresholds normalize on plugging superior canal dehiscence.

BACKGROUND: Diagnosis of the superior canal dehiscence syndrome (SCDS) relies on symptoms such as sound- or pressure-induced vertigo or oscillopsia, demonstration of sound or pressure-evoked vertical/torsional eye movements, and the presence of a defect in the bony roof overlying the superior semicircular canal. Lowered thresholds for eliciting vestibular-evoked myogenic potentials (VEMPs) provide additional conformation. OBJECTIVE: To examine VEMP characteristics before and after canal plugging for SCDS. METHODS: VEMPs evoked by air- and bone-conducted tones were measured from the sternocleidomastoid muscles (cVEMP) and periocular sites (oVEMP) of 20 normal volunteers, 10 newly diagnosed subjects with SCDS, and 12 subjects who underwent successful superior canal plugging. RESULTS: In all SCDS ears, thresholds for evoking VEMP using air-conducted tones were pathologically lowered, with average values of 83.85 +/- 1.40 dB sound pressure level (SPL) for cVEMP and 85.38 +/- 1.32 dB SPL for oVEMP, 20 to 30 dB below those of controls. Successful canal plugging resulted in normal reflex thresholds. For bone vibration, average thresholds in SCDS ears were 114.62 +/- 1.54 dB FL (force level) for cVEMP and 116.0 +/- 1.52 dB FL for oVEMP, 10 to 20 dB below controls, yet three SCDS ears had normal thresholds. CONCLUSIONS: Ocular and cervical vestibular-evoked myogenic potentials evoked by air-conducted sound are equally useful in the diagnosis and follow-up of superior canal dehiscence syndrome. Stimulus thresholds are consistently lowered upon presentation and normalize after corrective surgery. Thresholds for bone vibration, in contrast, have a lower diagnostic yield.