The role of cochlear and vestibular afferents in long-latency cervical vestibular evoked myogenic potentials.

OBJECTIVE: To examine the origin of cervical vestibular evoked myogenic potential (cVEMP) late waves (n34-p44) elicited with air-conducted click stimuli. DESIGN: Using a retrospective design, cVEMPs from normal volunteers were compared to those obtained from patients with vestibular and auditory pathologies. STUDY SAMPLE: (1) Normal volunteers (n = 56); (2) severe-to-profound sensorineural hearing loss (SNHL) with normal vestibular function (n = 21); (3) peripheral vestibular impairment with preserved hearing (n = 16); (4) total vestibulocochlear deficit (n = 23). RESULTS: All normal volunteers had ipsilateral-dominant early p13-n23 peaks. Late peaks were present bilaterally in 78%. The p13-n23 response was present in all patients with SNHL but normal vestibular function, and 43% had late waves. Statistical comparison of these patients to a subset of age-matched controls showed no significant difference in the frequencies, amplitudes or latencies of their ipsilateral early and late peaks. cVEMPs were absent in all patients with vestibular impairment. CONCLUSION: The presence of long-latency cVEMP waves was not dependent on the integrity of sensorineural hearing pathways, but instead correlated with intact vestibular function. This finding conflicts with the view that these late waves are cochlear in origin, and suggests that vestibular afferents may assume a more prominent role in their generation.

Machine learning models help differentiate between causes of recurrent spontaneous vertigo.

BACKGROUND: Vestibular migraine (VM) and Menière's disease (MD) are two common causes of recurrent spontaneous vertigo. Using history, video-nystagmography and audiovestibular tests, we developed machine learning models to separate these two disorders. METHODS: We recruited patients with VM or MD from a neurology outpatient facility. One hundred features from six "feature subsets": history, acute video-nystagmography and four laboratory tests (video head impulse test, vestibular-evoked myogenic potentials, caloric testing and audiogram) were used. We applied ten machine learning algorithms to develop classification models. Modelling was performed using three "tiers" of data availability to simulate three clinical settings. "Tier 1" used all available data to simulate the neuro-otology clinic, "Tier 2" used only history, audiogram and caloric test data, representing the general neurology clinic, and "Tier 3" used history alone as occurs in primary care. Model performance was evaluated using tenfold cross-validation. RESULTS: Data from 160 patients with VM and 114 with MD were used for model development. All models effectively separated the two disorders for all three tiers, with accuracies of 85.77-97.81%. The best performing algorithms (AdaBoost and Random Forest) yielded accuracies of 97.81% (95% CI 95.24-99.60), 94.53% (91.09-99.52%) and 92.34% (92.28-96.76%) for tiers 1, 2 and 3. The best feature subset combination was history, acute video-nystagmography, video head impulse test and caloric testing, and the best single feature subset was history. CONCLUSIONS: Machine learning models can accurately differentiate between VM and MD and are promising tools to assist diagnosis by medical practitioners with diverse levels of expertise and resources.

Effects of nonprescription therapies on vestibular migraine: a questionnaire-based observational study.

BACKGROUND: Vestibular migraine (VM) is a common cause of recurrent vertigo. Migraine headache preventative therapies are currently prescribed to control vertigo symptoms in VM. Clinical trials of nutraceuticals for migraine headache prevention have shown positive outcomes, but, to date, there have been no studies to assess their effectiveness in the management of VM. AIMS: To report the effects of nonprescription therapy management on VM symptoms. METHODS: We undertook a prospective, questionnaire-based assessment of patients diagnosed with VM between November 2019 and August 2021 at two Sydney tertiary referral clinics. Patients were advised on optimising sleep, hydration, exercise and nutrition and instructed to use an over-the-counter combination product containing riboflavin 200 mg, magnesium 150 mg, coenzyme Q10 75 mg and feverfew 200 mcg. Symptom severity and frequency were assessed using the Dizziness Handicap Inventory (DHI), the Vertigo Symptom Score short-form (VSS-sf) and two visual analogue scales for severity (VAS-s) and frequency (VAS-f) before and 3 months after commencing treatment. RESULT: In 82 participants (78% female; mean age, 44 ± 14 years) we recorded a decrease in DHI (mean, 16.8 [95% confidence interval (CI), 12.8-20.9], VSS-sf (9.3, 7.1-11.5), VAS-s (3.0, 2.2-3.8) and VAS-f (2.8, 2.1-3.4), equating to an improvement of 44.1%, 44.9%, 44.1% and 38.9% for each measure respectively. On the DHI and VSS-sf, 41 (50%) and 44 (53.7%) patients showed improvement in their symptoms; 39 (47.6%) and 36 (43.9%) patients noted no change and two patients reported worsening. The supplement was well-tolerated. CONCLUSIONS: The results provide preliminary evidence that VM symptom frequency and severity can be reduced by using nonprescription therapies.

Post Cochlear Implantation Vertigo: Ictal Nystagmus and Audiovestibular Test Characteristics.

OBJECTIVE: To investigate ictal nystagmus and audiovestibular characteristics in episodic spontaneous vertigo after cochlear implantation (CI). STUDY DESIGN: Retrospective and prospective case series. PATIENTS: Twenty-one CI patients with episodic spontaneous vertigo after implantation were recruited. INTERVENTIONS: Patient-initiated home video-oculography recordings were performed during one or more attacks of vertigo, using miniature portable home video-glasses. To assess canal and otolith function, video head-impulse tests (vHITs) and vestibular-evoked myogenic potential tests were conducted. MAIN OUTCOME MEASURES: Nystagmus slow-phase velocities (SPVs), the presence of horizontal direction-changing nystagmus, and post-CI audiovestibular tests. RESULTS: Main final diagnoses were post-CI secondary endolymphatic hydrops (48%) and exacerbation of existing Ménière's disease (29%). Symptomatic patients demonstrated high-velocity horizontal ictal-nystagmus (SPV, 44.2°/s and 68.2°/s in post-CI secondary endolymphatic hydrop and Ménière's disease). Direction-changing nystagmus was observed in 80 and 75%. Two were diagnosed with presumed autoimmune inner ear disease (SPV, 6.6°/s and 172.9°/s). One patient was diagnosed with probable vestibular migraine (15.1°/s).VHIT gains were 0.80 ± 0.20 (lateral), 0.70 ± 0.17 (anterior), and 0.62 ± 0.27 (posterior) in the implanted ear, with abnormal values in 33, 35, and 35% of each canal. Bone-conducted cervical and ocular vestibular-evoked myogenic potentials were asymmetric in 52 and 29% of patients (all lateralized to the implanted ear) with mean asymmetry ratios of 51.2 and 35.7%. Reversible reduction in vHIT gain was recorded in three acutely symptomatic patients. CONCLUSION: High-velocity, direction-changing nystagmus time-locked with vertigo attacks may be observed in post-CI implant vertigo and may indicate endolymphatic hydrops. Fluctuating vHIT gain may be an additional marker of a recurrent peripheral vestibulopathy.

Magnitude, variability and symmetry in head acceleration and jerk and their relationship to cervical and ocular vestibular evoked myogenic potentials.

BACKGROUND: Acceleration and changes in acceleration (jerk) stimulate vestibular otolith afferents. Bone-conducted (BC) vibration applied to the skull accelerates the head and produces short latency reflexes termed vestibular evoked myogenic potentials (VEMPs). OBJECTIVE: To determine the magnitude, variability and symmetry in head acceleration/jerk during VEMP recordings and investigate the relationship between head acceleration/jerk and VEMP properties. METHODS: 3D head accelerometery (sagittal, interaural and vertical axes) was recorded bilaterally in thirty-two healthy subjects during cervical (cVEMP) and ocular (oVEMP) recordings. BC 500 Hz sinusoidal tones were applied to the midline forehead using a positive polarity stimulus. RESULTS: The direction of induced acceleration/jerk was predominately backward, outward and downward on either side of the head during cVEMP and oVEMP recordings.Overall, acceleration/jerk was larger in the sagittal and interaural axes and peaked earlier in the interaural axis bilaterally. Acceleration was more symmetric in the sagittal and interaural axes whereas jerk symmetry did not differ between axes. Regression models did not show a systematic relationship between acceleration/jerk and either VEMP reflex. CONCLUSIONS: The pattern of skull acceleration/jerk was relatively consistent between the two sides of the head and across subjects, but there were differences in magnitude, leading to inter-side and inter-subject variability.

Subjective visual horizontal correlates better with ocular than with cervical vestibular evoked myogenic potentials.

OBJECTIVE: To examine the relationship between widely used otolith function tests: the Subjective Visual Horizontal (SVH) and Vestibular Evoked Myogenic Potentials (VEMP). METHODS: A retrospective analysis was performed on 301 patients who underwent SVH, ocular and cervical VEMP (oVEMP and cVEMP) tests on the same day. Correlations between the mean SVH tilt and amplitude asymmetry ratios for bone-conducted (BC) oVEMP and air-conducted (AC) cVEMP were examined. Diagnoses included vestibular neuritis, stroke, vestibular migraine, Meniere's disease, sudden sensorineural hearing loss (SSNHL) and vestibular schwannoma. RESULTS: SVH results were concordant with the oVEMP in 64% of cases and the cVEMP in 51%. Across all patients, SVH demonstrated a significant moderate correlation with BC oVEMP amplitude asymmetry ratios (r = 0.55, p < 0.001) and a weak correlation with AC cVEMP amplitude asymmetry ratios (r = 0.35, p < 0.001). A stronger correlation between SVH and oVEMPs was observed in patients with vestibular neuritis (r = 0.67, p < 0.001) and SSNHL (r = 0.76, p = 0.001). CONCLUSIONS: SVH correlates better with oVEMP than cVEMP symmetry. SIGNIFICANCE: This finding reinforces the hypothesis of a common utricular origin for both SVH and oVEMPs which is distinct from the saccular origin of cVEMPs.

The Relationship between the Subjective Visual Horizontal and Ocular Vestibular Evoked Myogenic Potentials in Acute Vestibular Neuritis.

OBJECT: Vestibular evoked myogenic potentials (VEMPs) and the subjective visual horizontal (SVH) (or vertical [SVV]) have both been considered tests of otolith function: ocular-VEMPs (oVEMPs) utricular function, cervical VEMPs (cVEMPs) saccular function. Some studies have reported association between decreased oVEMPs and SVH, whereas others have not. DESIGN: A retrospective study of test results. SETTING: A tertiary, neuro-otology clinic, Royal Prince Alfred Hospital, Sydney, Australia. METHOD: We analyzed results in 130 patients with acute vestibular neuritis tested within 5 days of onset. We sought correlations between the SVH, oVEMPs, and cVEMPs to air-conducted (AC) and bone-conducted (BC) stimulation. RESULTS: The SVH deviated to the side of lesion, in 123 of the 130 AVN patients, by 2.5 to 26.7 degrees. Ninety of the AVN patients (70%) had abnormal oVEMPs to AC, BC or both stimuli, on the AVN side (mean asymmetry ratio ± SD [SE]): (64 ± 45.0% [3.9]). Forty-three of the patients (35%) had impaired cVEMPs to AC, BC or both stimuli, on the AVN side, [22 ± 41.6% (4.1)]. The 90 patients with abnormal oVEMP values also had abnormal SVH. Correlations revealed a significant relationship between SVH offset and oVEMP asymmetry (r = 0.80, p < 0.001) and a weaker relationship between SVH offset and cVEMP asymmetry (r = 0.56, p < 0.001). CONCLUSIONS: These results indicate that after an acute unilateral vestibular lesion, before there has been a chance for vestibular compensation to occur, there is a significant correlation between the SVH, and oVEMP results. The relationship between SVH offset and oVEMP amplitude suggests that both tests measure utricular function.

Impact of Cochlear Implantation on Canal and Otolith Function.

OBJECTIVE: To quantify the impact of cochlear implantation (CI) on all five vestibular end-organs and on subjective ratings of post-CI dizziness. METHODS: Seventy-two patients undergoing unilateral CI were recruited for the study. All participants completed pre- and post-CI three-dimensional video head-impulse tests (3D vHITs) to assess semicircular-canal (SC) function, air- and bone-conducted (AC and BC) cervical and ocular vestibular-evoked myogenic potentials (cVEMPs and oVEMPs) to assess otolith-function and the dizziness handicap inventory (DHI) to measure self-perceived disability. RESULTS: Nineteen percent of patients reported new or worsened dizziness postsurgery. Post-CI abnormalities (new lesions and significant deteriorations) were seen in the AC cVEMP (48%), AC oVEMP (34%), BC cVEMP (10%), and BC oVEMP (7%); and lateral (L) (17%), posterior (P) (10%), and anterior (A) (13%) SC vHITs. CI surgery was more likely to affect the AC cVEMP compared with the other tests (χ2 test, p < 0.05). Fifty percent of patients reported no dizziness pre- and postsurgery. In the implanted ear, normal pre-CI vHIT gain was preserved in lateral semicircular canal (LSC) (69%), anterior semicircular canal (ASC) (74%), and posterior semicircular canal (PSC) (67%), and normal reflex amplitudes were found in AC cVEMP (25%), AC oVEMP (20%), BC cVEMP (59%), and BC oVEMP (74%). Statistically significant decreases were observed in LSC vHIT gain, AC cVEMP amplitude, and AC oVEMP amplitude postsurgery (p < 0.05). There was a significant moderate positive correlation between change in DHI scores and the summed vestibular deficit postsurgery (r(51) = 0.38, p < 0.05). CONCLUSION: CI can impact tests that assess all five vestibular end-organs and subjective ratings of dizziness. These results support pre and post-surgical vestibular testing and assist preoperative counseling and candidate selection.

A Portrait of Menière's Disease Using Contemporary Hearing and Balance Tests.

OBJECTIVE: Menière's disease (MD) is characterized by recurrent vertigo and fluctuating aural symptoms. Diagnosis is straightforward in typical presentations, but a proportion of patients present with atypical symptoms. Our aim is to profile the array of symptoms patients may initially present with and to analyze the vestibular and audiological test results of patients with a diagnosis of MD. DESIGN: A retrospective study of patient files. SETTING: A tertiary, neuro-otology clinic Royal Prince Alfred Hospital, Sydney, Australia. METHOD: We identified 375 patients. Their history, examination, vestibular-evoked myogenic potentials (VEMP), video head-impulse test, canal-paresis on caloric testing, subjective visual horizontal (SVH), electrocochleography, ictal nystagmus, and audiometry were assessed. RESULTS: Atypical presenting symptoms were disequilibrium (n = 49), imbalance (n = 13), drop-attacks (n = 12), rocking vertigo (n = 2), and unexplained vomiting (n = 3), nonspontaneous vestibular symptoms in 21.6%, fluctuation of aural symptoms only (46%), and headaches (31.2%). Low velocity, interictal spontaneous-nystagmus in 13.3% and persistent positional-nystagmus in 12.5%. Nystagmus recorded ictally in 90 patients was mostly horizontal (93%) and of high velocity (48 ±â€Š34°/s). Testing yielded abnormal caloric responses in 69.6% and abnormal video head impulse test 12.7%. Air-conducted cervical VEMPs were abnormal in 32.2% (mean asymmetry ratio [AR] 30.2 ±â€Š46.5%) and bone-conducted ocular VEMPs abnormal in 8.8% (AR 11.2 ±â€Š26.8%). Abnormal interictal SVH was in 30.6%, (ipsiversive n = 46 and contraversive n = 19). Mean pure-tone averages 50 dB ±â€Š23.5 and 20 dB ±â€Š13 for affected and unaffected ears. CONCLUSION: Menière's disease has a distinctive history, but atypical presentations with normal vestibular function and hearing are a diagnostic challenge delaying treatment initiation.

Vestibular function testing in the 21st century: video head impulse test, vestibular evoked myogenic potential, video nystagmography; which tests will provide answers?

PURPOSE OF REVIEW: To most neurologists, assessing the patient with vertigo is an unpleasant and worrisome task. A structured history and focused examination can be complemented by carefully selected laboratory tests, to reach an early and accurate diagnosis. We provide evidence-based recommendations for vestibular test selection. RECENT FINDINGS: The video head impulse test (vHIT), cervical and ocular vestibular evoked myogenic potential (VEMP) and home-video nystagmography are four modern, noninvasive methods of assessing vestibular function, which are equally applicable in the hospital and office-practice. Collectively, they enable assessment of all five vestibular end-organs. The prevalence and patterns of test abnormalities are distinct for each vestibular disorder. We summarize typical abnormalities encountered in four common vestibular syndromes. SUMMARY: In the context of acute vestibular syndrome, an abnormal vHIT with low gain and large amplitude refixation saccades and an asymmetric oVEMP separates innocuous vestibular neuritis from stroke. In episodic spontaneous vertigo, high-velocity ictal nystagmus and asymmetric cVEMP help separate Ménière's disease from vestibular migraine. In chronic imbalance, all three tests help detect unilateral or bilateral vestibular loss as the root cause. Recurrent positional vertigo requires no laboratory test and can be diagnosed and treated at the bedside, guided by video nystagmography.

Subjective Cognitive Dysfunction in Patients with Dizziness and Vertigo.

INTRODUCTION: Patients with vestibular disorders sometimes report cognitive difficulties, but there is no consensus about the type or degree of cognitive complaint. We therefore investigated subjective cognitive dysfunction in a well-defined sample of neuro-otology patients and used demographic factors and scores from a measure of depression, anxiety, and stress to control for potential confounding factors. METHODS: We asked 126 neuro-otology clinic outpatients whether they experienced difficulties with thinking, memory, or concentration as a result of dizziness or vertigo. They and 42 nonvertiginous control subjects also completed the Neuropsychological Vertigo Inventory (NVI, which measures cognitive, emotional, vision, and motor complaints), the Everyday Memory Questionnaire (EMQ), and Depression, Anxiety, and Stress Scales (DASS). RESULTS: In the initial interview questions, 60% of patients reported experiencing cognitive difficulties. Cognitive questionnaire scores were positively correlated with the overall DASS score and to a lesser extent with age and gender. Therefore, we compared patients and controls on the NVI and EMQ, using these mood and demographic variables as covariates. Linear regression analyses revealed that patients scored significantly worse on the total NVI, NVI cognitive composite, and 3 individual NVI cognition subscales (Attention, Space Perception, and Time Perception), but not the EMQ. Patients also scored significantly worse on the NVI Emotion and Motor subscales. CONCLUSIONS: Patients with dizziness and vertigo reported high levels of cognitive dysfunction, affecting attention, perceptions of space and time. Although perceptions of cognitive dysfunction were correlated with emotional distress, they were significantly elevated in patients over and above the impact of depression, anxiety, or stress.

Comparison of the Effects of Matching and Normalization on the Cervical Vestibular Evoked Myogenic Potential.

HYPOTHESIS: We compared two means of mitigating the effect of sternocleidomastoid (SCM) contraction strength on the cervical vestibular evoked myogenic potential (cVEMP): contraction matching and amplitude normalization. BACKGROUND: SCM muscle contraction strength affects the amplitude of the cVEMP which can impact measures of inter-side asymmetry and diagnostic outcomes. METHODS: In 19 normal subjects, we investigated the effect of muscle contraction variation within a cVEMP recording. We then compared cVEMP recordings on the right and left sides with matched and unmatched muscle contraction strength using raw amplitudes and amplitude ratios (i.e., normalized amplitudes). RESULTS: Contraction variability had significant effects on small sections of a cVEMP recording, but there was no significant effect on overall cVEMP amplitude, suggesting that the cVEMP is relatively unaffected by variable effort during a recording. Matching the contraction across the two sides (d = 0.53, p = 0.016) and amplitude normalization (d = 0.43, p = 0.004) both significantly reduced inter-side asymmetry, but normalization had no additional benefit once the sides were matched (interaction effect, p = 0.019). cVEMPs recorded with matched contractions had the smallest range of asymmetry values. CONCLUSION: The study shows that controlling the background contraction during a cVEMP recording, either by using similar contractions for each trial or by normalizing the amplitude, reduces cVEMP asymmetry and can prevent incorrect results in the minority of subjects who make asymmetric muscle contractions.

Quantifying the effects of electrode placement and montage on measures of cVEMP amplitude and muscle contraction.

BACKGROUND: The cervical vestibular evoked myogenic potential (cVEMP) can be affected by the recording parameters used to quantify the response. OBJECTIVE: We investigated the effects of electrode placement and montage on the variability and symmetry of sternocleidomastoid (SCM) contraction strength and cVEMP amplitude. METHODS: We used inter-side asymmetries in electrode placement to mimic small clinical errors in twenty normal subjects. cVEMPs were recorded at three active electrode sites and referred to the distal SCM tendon (referential montages: upper, conventional and lower). Additional bipolar montages were constructed offline to measure SCM contraction strength using closely-spaced electrode pairs (bipolar montages: superior, lower and outer). RESULTS: The conventional montage generally produced the largest cVEMP amplitudes (P < 0.001). SCM contraction strength was larger for referential montages than bipolar ones (P < 0.001). Inter-side electrode position errors produced large variations in cVEMP and SCM contraction strength asymmetries in some subjects, producing erroneous abnormal test results. CONCLUSION: Recording locations affect cVEMP amplitude and SCM contraction strength. In most cases, small changes in electrode position had only minor effects but, in a minority of subjects, the different montages produced large changes in cVEMP and contraction amplitudes and asymmetry, potentially affecting test outcomes.

Nystagmus characteristics of healthy controls.

BACKGROUND: Healthy controls exhibit spontaneous and positional nystagmus which needs to be distinguished from pathological nystagmus. OBJECTIVE: Define nystagmus characteristics of healthy controls using portable video-oculography. METHODS: One-hundred and one asymptomatic community-dwelling adults were prospectively recruited. Participants answered questions regarding their audio-vestibular and headache history and were sub-categorized into migraine/non-migraine groups. Portable video-oculography was conducted in the upright, supine, left- and right-lateral positions, using miniature take-home video glasses. RESULTS: Upright position spontaneous nystagmus was found in 30.7% of subjects (slow-phase velocity (SPV)), mean 1.1±2.2 degrees per second (°/s) (range 0.0 - 9.3). Upright position spontaneous nystagmus was horizontal, up-beating or down-beating in 16.7, 7.9 and 5.9% of subjects. Nystagmus in at least one lying position was found in 70.3% of subjects with 56.4% showing nystagmus while supine, and 63.4% in at least one lateral position. While supine, 20.8% of subjects showed up-beating nystagmus, 8.9% showed down-beating, and 26.7% had horizontal nystagmus. In the lateral positions combined, 37.1% displayed horizontal nystagmus on at least one side, while 6.4% showed up-beating, 6.4% showed down-beating. Mean nystagmus SPVs in the supine, right and left lateral positions were 2.2±2.8, 2.7±3.4, and 2.1±3.2°/s. No significant difference was found between migraine and non-migraine groups for nystagmus SPVs, prevalence, vertical vs horizontal fast-phase, or low- vs high-velocity nystagmus (<5 vs > 5°/s). CONCLUSIONS: Healthy controls without a history of spontaneous vertigo show low velocity spontaneous and positional nystagmus, highlighting the importance of interictal nystagmus measures when assessing the acutely symptomatic patient.

Bone-Conducted oVEMP Latency Delays Assist in the Differential Diagnosis of Large Air-Conducted oVEMP Amplitudes.

Background: A sensitive test for Superior Semicircular Canal Dehiscence (SCD) is the air-conducted, ocular vestibular evoked myogenic potential (AC oVEMP). However, not all patients with large AC oVEMPs have SCD. This retrospective study sought to identify alternate diagnoses also producing enlarged AC oVEMPs and investigated bone-conducted (BC) oVEMP outcome measures that would help differentiate between these, and cases of SCD. Methods: We reviewed the clinical records and BC oVEMP results of 65 patients (86 ears) presenting with dizziness or balance problems who underwent CT imaging to investigate enlarged 105 dB nHL click AC oVEMP amplitudes. All patients were tested with BC oVEMPs using two different stimuli (1 ms square-wave pulse and 8 ms 125 Hz sine wave). Logistic regression and odds ratios were used to determine the efficacy of BC oVEMP amplitudes and latencies in differentiating between enlarged AC oVEMP amplitudes due to dehiscence from those with an alternate diagnosis. Results: Fifty-three ears (61.6%) with enlarged AC oVEMP amplitudes were identified as having frank dehiscence on imaging; 33 (38.4%) had alternate diagnoses that included thinning of the bone covering (near dehiscence, n = 13), vestibular migraine (n = 12 ears of 10 patients), enlarged vestibular aqueduct syndrome (n = 2) and other causes of recurrent episodic vertigo (n = 6). BC oVEMP amplitudes of dehiscent and non-dehiscent ears were not significantly different (p > 0.05); distributions of both groups overlapped with the range of healthy controls. There were significant differences in BC oVEMP latencies between dehiscent and non-dehiscent ears for both stimuli (p < 0.001). A prolonged n1 125 Hz latency (>11.5 ms) was the best predictor of dehiscence (odd ratio = 27.8; 95% CI:7.0-111.4); abnormal n1 latencies were identified in 79.2% of ears with dehiscence compared with 9.1% of ears without dehiscence. Conclusions: A two-step protocol of click AC oVEMP amplitudes and 125 Hz BC oVEMP latency measures optimizes the specificity of VEMP testing in SCD.

Bone-conducted vestibular and stretch reflexes in human neck muscles.

In normal humans, tapping the forehead produces a neck muscle reflex that is used clinically to test vestibular function, the cervical vestibular evoked myogenic potential (cVEMP). As stretch receptors can also be activated by skull taps, we investigated the origin of the early and late peaks of the bone-conducted cVEMP. In twelve normal participants, we differentially stimulated the vestibular and neck stretch receptors by applying vibration to the forehead (activating both vestibular and stretch receptors) and to the sternum (activating mainly stretch receptors). Patients with bilateral vestibulopathy (BVP; n = 26) and unilateral vestibular loss (uVL; n = 17) were also investigated for comparison. Comparison of peaks in normal subjects suggested that the early peaks were vestibular-dependent, while the later peaks had mixed vestibular and stretch input. The late peaks were present but small (1.1 amplitude ratio) in patients with BVP and absent VEMPs, confirming that they do not strictly depend on vestibular function, and largest in age-matched controls (1.5 amplitude ratio, p = 0.049), suggesting that there is an additional vestibular reflex at this latency (approx. 30 ms). Patients with uVL had larger late peaks on the affected than the normal side (1.4 vs 1.0 amplitude ratio, p = 0.034). The results suggest that the early responses in SCM to skull vibration in humans are vestibular-dependent, while there is a late stretch reflex bilaterally and a late vestibular reflex in the contralateral muscle.

Vestibular-Evoked Myogenic Potential Testing in Vestibular Localization and Diagnosis.

Vestibular-evoked myogenic potentials (VEMPs) are short-latency, otolith-dependent reflexes recorded from the neck and eye muscles. They are widely used in neuro-otology clinics as tests of otolith function. Cervical VEMPs are recorded from the neck muscles and reflect predominantly saccular function, while ocular VEMPs are reflexes of the extraocular muscles and reflect utricular function. They have an important role in the diagnosis of superior canal dehiscence syndrome and provide complementary information about otolith function that is useful in the diagnosis of other vestibular disorders. Like other evoked potentials, they can provide important localizing information about lesions that may occur along the VEMP pathway. This review will describe the VEMP abnormalities seen in common disorders of the vestibular system and its pathways.

Evidence of a Vestibular Origin for Crossed-Sternocleidomastoid Muscle Responses to Air-Conducted Sound.

OBJECTIVES: Small, excitatory surface potentials can sometimes be recorded from the contralateral sternocleidomastoid muscle (SCM) following monaural acoustic stimulation. Little is known about the physiological properties of these crossed reflexes. In this study, we sought the properties of crossed SCM responses and through comparison with other cochlear and vestibular myogenic potentials, their likely receptor origin. DESIGN: Surface potentials were recorded from the ipsilateral and contralateral SCM and postauricular (PAM) muscles of 11 healthy volunteers, 4 patients with superior canal dehiscence and 1 with profound hearing loss. Air-conducted clicks of 105 dB nHL and tone bursts (250 to 4000 Hz) of 100 dB nHL were presented monaurally through TDH 49 headphones during head elevation. Click-evoked responses were recorded under two conditions of gaze in random order: gaze straight ahead and rotated hard toward the contralateral recording electrodes. Amplitudes (corrected and uncorrected) and latencies for crossed SCM responses were compared with vestibular (ipsilateral SCM) and cochlear (PAM) responses between groups and across the different recording conditions. RESULTS: Surface waveforms were biphasic; positive-negative for the ipsilateral SCM, and negative-positive for the contralateral SCM and PAM. There were significant differences in the amplitudes and latencies (p = 0.004) for click responses of healthy controls across recording sites. PAM responses had the largest mean-corrected amplitudes (2.3 ± 2.8) and longest latencies (13.0 ± 1.2 msec), compared with ipsilateral (1.6 ± 0.5; 12.0 ± 0.7 msec) and contralateral (0.8 ± 0.3; 10.4 ± 1.0 msec) SCM responses. Uncorrected amplitudes and muscle activation for PAM increased by 104.4% and 46.8% with lateral gaze respectively, whereas SCM responses were not significantly affected. Click responses of patients with superior canal dehiscence followed a similar latency, amplitude, and gaze modulation trend as controls. SCM responses were preserved in the patient with profound hearing loss, yet all PAM were absent. There were significant differences in the frequency tuning of the three reflexes (p < 0.001). Tuning curves of healthy controls were flat for PAM and down sloping for ipsilateral and contralateral SCM responses. For superior canal dehiscence, they were rising for PAM and slightly down sloping for SCM responses. CONCLUSIONS: Properties of crossed SCM responses were similar, though not identical, to those of ipsilateral SCM responses and are likely to be predominantly vestibular in origin. They are unlikely to represent volume conduction from the PAM as they were unaffected by lateral gaze, were shorter in latency, and had different tuning properties. The influence of crossed vestibulo-collic pathways should be considered when interpreting cervical vestibular-evoked myogenic potentials recorded under conditions of binaural stimulation.

Investigating short latency subcortical vestibular projections in humans: what have we learned?

Vestibular evoked myogenic potentials (VEMPs) are now widely used for the noninvasive assessment of vestibular function and diagnosis in humans. This review focuses on the origin, properties, and mechanisms of cervical VEMPs and ocular VEMPs; how these reflexes relate to reports of vestibular projections to brain stem and cervical targets; and the physiological role of (otolithic) cervical and ocular reflexes. The evidence suggests that both VEMPs are likely to represent the effects of excitation of irregularly firing otolith afferents. While the air-conducted cervical VEMP appears to mainly arise from excitation of saccular receptors, the ocular VEMP evoked by bone-conducted stimulation, including impulsive bone-conducted stimuli, mainly arises from utricular afferents. The surface responses are generated by brief changes in motor unit firing. The effects that have been demonstrated are likely to represent otolith-dependent vestibulocollic and vestibulo-ocular reflexes, both linear and torsional. These observations add to previous reports of short latency otolith projections to the target muscles in the neck (sternocleidomastoid and splenius) and extraocular muscles (the inferior oblique). New insights have been provided by the investigation and application of these techniques.