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.

Subjective and objective responses to caloric stimulation help separate vestibular migraine from other vestibular disorders

BACKGROUND

Nystagmus generated during bithermal caloric test assesses the horizontal vestibulo-ocular-reflex. Any induced symptoms are considered unwanted side effects rather than diagnostic information.

AIM

We hypothesized that nystagmus slow-phase-velocity (SPV) and subjective symptoms during caloric testing would be higher in vestibular migraine (VM) patients compared with peripheral disorders such as Meniere's disease (MD) and non-vestibular dizziness (NVD).

METHODS

Consecutive patients (n = 1373, 60% female) referred for caloric testing were recruited. During caloric irrigations, patients scored their subjective sensations. We assessed objective-measures, subjective vertigo (SVS), subjective nausea (SNS), and test completion status.

RESULTS

Nystagmus SPV for VM, MD (unaffected side), and NVD were 29 ± 12.8, 30 ± 15.4, and 28 ± 14.2 for warm irrigation and 24 ± 8.9, 22 ± 10.0, and 25 ± 12.8 for cold-irrigation. The mean SVS were 2.5 ± 1.1, 1.5 ± 1.33, and 1.5 ± 1.42 for warm irrigation and 2.2 ± 1.1, 1.1 ± 1.19, and 1.1 ± 1.16 for cold-irrigation. Age was significantly correlated with SVS and SNS, (p < 0.001) for both. The SVS and SNS were significantly higher in VM compared with non-VM groups (p < 0.001), and there was no difference in nystagmus SPV. VM patients SVS was significantly different to the SVS of migraineurs in the other diagnostic groups (p < 0.001). Testing was incomplete for 34.4% of VM and 3.2% of MD patients. To separate VM from MD, we computed a composite value representing the caloric data, with 83% sensitivity and 71% specificity. Application of machine learning to these metrics plus patient demographics yielded better separation (96% sensitivity and 85% specificity).

CONCLUSION

Perceptual differences between VM and non-VM patients during caloric stimulation indicate that subjective ratings during caloric testing are meaningful measures. Combining objective and subjective measures could provide optimal separation of VM from MD.

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.

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.

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.

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.

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 ± 34°/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 ± 46.5%) and bone-conducted ocular VEMPs abnormal in 8.8% (AR 11.2 ± 26.8%). Abnormal interictal SVH was in 30.6%, (ipsiversive n = 46 and contraversive n = 19). Mean pure-tone averages 50 dB ± 23.5 and 20 dB ± 13 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.

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.

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.

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.

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.

Sound-evoked vestibular projections to the splenius capitis in humans: comparison with the sternocleidomastoid muscle

The short-latency vestibulo-collic reflex in humans is well defined for only the sternocleidomastoid (SCM) neck muscle. However, other neck muscles also receive input from the balance organs and participate in neck stabilization. We therefore investigated the sound-evoked vestibular projection to the splenius capitis (SC) muscles by comparing surface and single motor unit responses in the SC and SCM muscles in 10 normal volunteers. We also recorded surface responses in patients with unilateral vestibular loss but preserved hearing and hearing loss but preserved vestibular function. The single motor unit responses were predominantly inhibitory, and the strongest responses were recorded in the contralateral SC and ipsilateral SCM. In both cases there was a significant decrease or gap in single motor unit activity, in SC at 11.7 ms for 46/66 units and in SCM at 12.7 ms for 51/58 motor units. There were fewer significant responses in the ipsilateral SC and contralateral SCM muscles, and they consisted primarily of weak increases in activity. Surface responses recorded over the contralateral SC were positive-negative during neck rotation, similar to the ipsilateral cervical vestibular evoked myogenic potential in SCM. Responses in SC were present in the patients with hearing loss and absent in the patient with vestibular loss, confirming their vestibular origin. The results describe a pattern of inhibition consistent with the synergistic relationship between these muscles for axial head rotation, with the crossed vestibular projection to the contralateral SC being weaker than the ipsilateral projection to the SCM.

NEW & NOTEWORTHY We used acoustic vestibular stimulation to investigate the saccular projections to the splenius capitis (SC) and sternocleidomastoid (SCM) muscles in humans. Single motor unit recordings from within the muscles demonstrated strong inhibitory projections to the contralateral SC and ipsilateral SCM muscles and weak excitatory projections to the opposite muscle pair. This synergistic pattern of activation is consistent with a role for the reflex in axial rotation of the head.

Vestibular evoked myogenic potentials in practice: Methods, pitfalls and clinical applications

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Vestibular evoked myogenic potentials (VEMPs) are used to test the otolith organs in patients with vertigo and imbalance.

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This review discusses the optimal procedures for recording VEMPs and the pitfalls commonly encountered by clinicians.

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Better understanding of VEMP methodology should lead to improved quality of recordings.

Vestibular evoked myogenic potentials (VEMPs) are a useful and increasingly popular component of the neuro-otology test battery. These otolith-dependent reflexes are produced by stimulating the ears with air-conducted sound or skull vibration and recorded from surface electrodes placed over the neck (cervical VEMPs) and eye muscles (ocular VEMPs). VEMP abnormalities have been reported in various diseases of the ear and vestibular system, and VEMPs have a clear role in the diagnosis of superior semicircular canal dehiscence. However there is significant variability in the methods used to stimulate the otoliths and record the reflexes. This review discusses VEMP methodology and provides a detailed theoretical background for the techniques that are typically used. The review also outlines the common pitfalls in VEMP recording and the clinical applications of VEMPs.

μVEMP: A Portable Interface to Record Vestibular Evoked Myogenic Potentials (VEMPs) With a Smart Phone or Tablet

Background: Cervical VEMPs and ocular VEMPs are tests for evaluating otolith function in clinical practice. We developed a simple, portable and affordable device to record VEMP responses on patients, named μVEMP. Our aim was to validate and field test the new μVEMP device. Methods: We recorded cervical VEMPs and ocular VEMPs in response to bone conducted vibration using taps tendon hammer to the forehead (Fz) and to air conducted sounds using clicks. We simultaneously recorded VEMP responses (same subject, same electrode, same stimuli) in three healthy volunteers (2 females, age range: 29-57 years) with the μVEMP device and with a standard research grade commercial (CED) system used in clinics. We also used the μVEMP device to record VEMP responses from six patients (6 females, age mean±SD: 50.3 ± 20.8 years) with classical peripheral audio-vestibular diseases (unilateral vestibular neuritis, unilateral neurectomy, bilateral vestibular loss, unilateral superior canal dehiscence, unilateral otosclerosis). Results: The first part of this paper compared the devices using simultaneous recordings. The average of the concordance correlation coefficient was rc = 0.997 ± 0.003 showing a strong similarity between the measures. VEMP responses recorded with the μVEMP device on patients with audio-vestibular diseases were similar to those typically found in the literature. Conclusions: We developed, validated and field tested a new device to record ocular and cervical VEMPs in response to sound and vibration.This new device is portable (powered by a phone or tablet) with pocket-size dimensions (105 × 66 × 27 mm) and light weight (150 g). Although further studies and normative data are required, our μVEMP device is simpler (easier to use) and potentially more accessible than standard, commercially available equipment.

The Contributions of Vestibular Evoked Myogenic Potentials and Acoustic Vestibular Stimulation to Our Understanding of the Vestibular System

Vestibular-evoked myogenic potentials (VEMPs) are short-latency muscle reflexes typically recorded from the neck or eye muscles with surface electrodes. They are used clinically to assess otolith function, but are also interesting as they can provide information about the vestibular system and its activation by sound and vibration. Since the introduction of VEMPs more than 25 years ago, VEMPs have inspired animal and human research on the effects of acoustic vestibular stimulation on the vestibular organs, their projections and the postural muscles involved in vestibular reflexes. Using a combination of recording techniques, including single motor unit recordings, VEMP studies have enhanced our understanding of the excitability changes underlying the sound-evoked vestibulo-collic and vestibulo-ocular reflexes. Studies in patients with diseases of the vestibular system, such as superior canal dehiscence and Meniere's disease, have shown how acoustic vestibular stimulation is affected by physical changes in the vestibule, and how sound-evoked reflexes can detect these changes and their resolution in clinical contexts. This review outlines the advances in our understanding of the vestibular system that have occurred following the renewed interest in sound and vibration as a result of the VEMP.

Vestibular-Evoked Myogenic Potentials in Bilateral Vestibulopathy

Bilateral vestibulopathy (BVP) is a chronic condition in which patients have a reduction or absence of vestibular function in both ears. BVP is characterized by bilateral reduction of horizontal canal responses; however, there is increasing evidence that otolith function can also be affected. Cervical and ocular vestibular-evoked myogenic potentials (cVEMPs/oVEMPs) are relatively new tests of otolith function that can be used to test the saccule and utricle of both ears independently. Studies to date show that cVEMPs and oVEMPs are often small or absent in BVP but are in the normal range in a significant proportion of patients. The variability in otolith function is partly due to the heterogeneous nature of BVP but is also due to false negative and positive responses that occur because of the large range of normal VEMP amplitudes. Due to their variability, VEMPs are not part of the diagnosis of BVP; however, they are helpful complementary tests that can provide information about the extent of disease within the labyrinth. This article is a review of the use of VEMPs in BVP, summarizing the available data on VEMP abnormalities in patients and discussing the limitations of VEMPs in diagnosing bilateral loss of otolith function.

Disorders of the inner-ear balance organs and their pathways

Disorders of the inner-ear balance organs can be grouped by their manner of presentation into acute, episodic, or chronic vestibular syndromes. A sudden unilateral vestibular injury produces severe vertigo, nausea, and imbalance lasting days, known as the acute vestibular syndrome (AVS). A bedside head impulse and oculomotor examination helps separate vestibular neuritis, the more common and innocuous cause of AVS, from stroke. Benign positional vertigo, a common cause of episodic positional vertigo, occurs when otoconia overlying the otolith membrane falls into the semicircular canals, producing brief spells of spinning vertigo triggered by head movement. Benign positional vertigo is diagnosed by a positional test, which triggers paroxysmal positional nystagmus in the plane of the affected semicircular canal. Episodic spontaneous vertigo caused by vestibular migraine and Ménière's disease can sometimes prove hard to separate. Typically, Ménière's disease is associated with spinning vertigo lasting hours, aural fullness, tinnitus, and fluctuating hearing loss while VM can produce spinning, rocking, or tilting sensations and light-headedness lasting minutes to days, sometimes but not always associated with migraine headaches or photophobia. Injury to both vestibular end-organs results in ataxia and oscillopsia rather than vertigo. Head impulse testing, dynamic visual acuity, and matted Romberg tests are abnormal while conventional neurologic assessments are normal. A defect in the bony roof overlying the superior semicircular canal produces vertigo and oscillopsia provoked by loud sound and pressure (when coughing or sneezing). Three-dimensional temporal bone computed tomography scan and vestibular evoked myogenic potential testing help confirm the diagnosis of superior canal dehiscence. Collectively, these clinical syndromes account for a large proportion of dizzy and unbalanced patients.

Bilateral vestibulopathy: Diagnostic criteria Consensus document of the Classification Committee of the Bárány Society

This paper describes the diagnostic criteria for bilateral vestibulopathy (BVP) by the Classification Committee of the Bárány Society. The diagnosis of BVP is based on the patient history, bedside examination and laboratory evaluation. Bilateral vestibulopathy is a chronic vestibular syndrome which is characterized by unsteadiness when walking or standing, which worsen in darkness and/or on uneven ground, or during head motion. Additionally, patients may describe head or body movement-induced blurred vision or oscillopsia. There are typically no symptoms while sitting or lying down under static conditions.

The diagnosis of BVP requires bilaterally significantly impaired or absent function of the vestibulo-ocular reflex (VOR). This can be diagnosed for the high frequency range of the angular VOR by the head impulse test (HIT), the video-HIT (vHIT) and the scleral coil technique and for the low frequency range by caloric testing. The moderate range can be examined by the sinusoidal or step profile rotational chair test.

For the diagnosis of BVP, the horizontal angular VOR gain on both sides should be <0.6 (angular velocity 150–300°/s) and/or the sum of the maximal peak velocities of the slow phase caloric-induced nystagmus for stimulation with warm and cold water on each side <6°/s and/or the horizontal angular VOR gain <0.1 upon sinusoidal stimulation on a rotatory chair (0.1 Hz, Vmax = 50°/sec) and/or a phase lead >68 degrees (time constant of <5 seconds). For the diagnosis of probable BVP the above mentioned symptoms and a bilaterally pathological bedside HIT are required.

Complementary tests that may be used but are currently not included in the definition are: a) dynamic visual acuity (a decrease of ≥0.2 logMAR is considered pathological); b) Romberg (indicating a sensory deficit of the vestibular or somatosensory system and therefore not specific); and c) abnormal cervical and ocular vestibular-evoked myogenic potentials for otolith function.

At present the scientific basis for further subdivisions into subtypes of BVP is not sufficient to put forward reliable or clinically meaningful definitions. Depending on the affected anatomical structure and frequency range, different subtypes may be better identified in the future: impaired canal function in the low- or high-frequency VOR range only and/or impaired otolith function only; the latter is evidently very rare.

Bilateral vestibulopathy is a clinical syndrome and, if known, the etiology (e.g., due to ototoxicity, bilateral Menière’s disease, bilateral vestibular schwannoma) should be added to the diagnosis. Synonyms include bilateral vestibular failure, deficiency, areflexia, hypofunction and loss.

cVEMP morphology changes with recording electrode position, but single motor unit activity remains constant

Cervical vestibular evoked myogenic potentials (cVEMPs) recorded over the lower quarter of the sternocleidomastoid (SCM) muscle in normal subjects may have opposite polarity to those recorded over the midpoint. It has thus been suggested that vestibular projections to the lower part of SCM might be excitatory rather than inhibitory. We tested the hypothesis that the SCM muscle receives both inhibitory and excitatory vestibular inputs. We recorded cVEMPs in 10 normal subjects with surface electrodes placed at multiple sites along the anterior (sternal) component of the SCM muscle. We compared several reference sites: sternum, ipsilateral and contralateral earlobes, and contralateral wrist. In five subjects, single motor unit responses were recorded at the upper, middle, and lower parts of the SCM muscle using concentric needle electrodes. The surface cVEMP had the typical positive-negative polarity at the midpoint of the SCM muscle. In all subjects, as the recording electrode was moved toward each insertion point, p13 amplitude became smaller and p13 latency increased, then the polarity inverted to a negative-positive waveform (n1-p1). Changing the reference site did not affect reflex polarity. There was a significant short-latency change in activity in 61/63 single motor units, and in each case this was a decrease or gap in firing, indicating an inhibitory reflex. Single motor unit recordings showed that the reflex was inhibitory along the entire SCM muscle. The cVEMP surface waveform inversion near the mastoid and sternal insertion points likely reflects volume conduction of the potential occurring with increasing distance from the motor point.

Vestibular-evoked myogenic potentials

The vestibular-evoked myogenic potential (VEMP) is a short-latency potential evoked through activation of vestibular receptors using sound or vibration. It is generated by modulated electromyographic signals either from the sternocleidomastoid muscle for the cervical VEMP (cVEMP) or the inferior oblique muscle for the ocular VEMP (oVEMP). These reflexes appear to originate from the otolith organs and thus complement existing methods of vestibular assessment, which are mainly based upon canal function. This review considers the basis, methodology, and current applications of the cVEMP and oVEMP in the assessment and diagnosis of vestibular disorders, both peripheral and central.

Clinical utility of ocular vestibular-evoked myogenic potentials (oVEMPs)

Over the last years, vestibular-evoked myogenic potentials (VEMPs) have been established as clinical tests of otolith function. Complementary to the cervical VEMPs, which assess mainly saccular function, ocular VEMPs (oVEMPs) test predominantly utricular otolith function. oVEMPs are elicited either with air-conducted (AC) sound or bone-conducted (BC) skull vibration and are recorded from beneath the eyes during up-gaze. They assess the vestibulo-ocular reflex and are a crossed excitatory response originating from the inferior oblique eye muscle. Enlarged oVEMPs have proven to be sensitive for screening of superior canal dehiscence, while absent oVEMPs indicate a loss of superior vestibular nerve otolith function, often seen in vestibular neuritis (VN) or vestibular Schwannoma.

Contrasting phase effects on vestibular evoked myogenic potentials (VEMPs) produced by air- and bone-conducted stimuli

We have studied the effects of stimulus phase on the latency and amplitude of cVEMPs and oVEMPs by reanalysing data from Lim et al. (Exp Brain Res 224:437-445, 2013) in which alternating phase was used. Responses for the different initial stimulus phase, either positive or negative, were separated and reaveraged. We found that the phase (compressive or rarefactive) of AC 500-Hz stimuli had no significant effect on either latency or amplitude of the responses. Conversely, phase (positive = motor towards subjects) did alter the effects of BC 500-Hz stimulation. For cVEMPs, phase consistently affected initial latency with earlier responses for positive stimuli, while, for stimulation at the mastoid, negative onset phase gave larger responses. For the oVEMP, effects were different for the two sites of BC stimulation. At the forehead, the response appeared to invert, whereas at the mastoid there appeared to be a delay of the initial response. Related to this, the effect of phase for the two sites was opposite: at the mastoid, positive responses were earlier but negative were larger (particularly for long stimuli). At the forehead, the effect was the opposite: negative onset stimuli evoked earlier responses, whereas positive onset evoked larger responses. These findings indicate a basic difference in the way that AC and BC stimuli activate vestibular receptors and also indicate that the effects of phase of BC stimulation depend on location. Stimulus alternation does little to affect the response to AC stimulation but obscures the effects of BC stimuli, particularly for the oVEMP.

Ethanol consumption impairs vestibulo-ocular reflex function measured by the video head impulse test and dynamic visual acuity

Ethanol affects many parts of the nervous system, from the periphery to higher cognitive functions. Due to the established effects of ethanol on vestibular and oculomotor function, we wished to examine its effect on two new tests of the vestibulo-ocular reflex (VOR): the video head impulse test (vHIT) and dynamic visual acuity (DVA). We tested eight healthy subjects with no history of vestibular disease after consumption of standardized drinks of 40% ethanol. We used a repeated measures design to track vestibular function over multiple rounds of ethanol consumption up to a maximum breath alcohol concentration (BrAC) of 1.38 per mil. All tests were normal at baseline. VOR gain measured by vHIT decreased by 25% at the highest BrAC level tested in each subject. Catch-up saccades were negligible at baseline and increased in number and size with increasing ethanol consumption (from 0.13° to 1.43° cumulative amplitude per trial). DVA scores increased by 86% indicating a deterioration of acuity, while static visual acuity (SVA) remained unchanged. Ethanol consumption systematically impaired the VOR evoked by high-acceleration head impulses and led to a functional loss of visual acuity during head movement.

The effect of alcohol on cervical and ocular vestibular evoked myogenic potentials in healthy volunteers

OBJECTIVE

We investigated the effect of alcohol on the cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs). As alcohol produces gaze-evoked nystagmus (GEN), we also tested the effect of nystagmus independent of alcohol by recording oVEMPs during optokinetic stimulation (OKS).

METHODS

The effect of alcohol was tested in 14 subjects over multiple rounds of alcohol consumption up to a maximum breath alcohol concentration (BrAC) of 1.5‰ (mean 0.97‰). The effect of OKS was tested in 11 subjects at 5, 10 and 15deg/sec.

RESULTS

oVEMP amplitude decreased from baseline to the highest BrAC level by 27% (range 5-50%, P<0.001), but there was no significant effect on oVEMP latency or cVEMP amplitude or latency. There was a significant negative effect of OKS on oVEMP amplitude (16%, P=0.006).

CONCLUSIONS

We found a selective effect of alcohol on oVEMP amplitude, but no effect on the cVEMP. Vertical nystagmus elicited by OKS reduced oVEMP amplitude.

SIGNIFICANCE

Alcohol selectively affects oVEMP amplitude. Despite the effects of alcohol and nystagmus, both reflexes were reliably recorded in all subjects and conditions. An absent response in a patient affected by alcohol or nystagmus indicates a vestibular deficit.

Why do oVEMPs become larger when you look up? Explaining the effect of gaze elevation on the ocular vestibular evoked myogenic potential

OBJECTIVES

The ocular vestibular evoked myogenic potential (oVEMP) is a vestibular reflex recorded from the inferior oblique (IO) muscles, which increases in amplitude during eye elevation. We investigated whether this effect of gaze elevation could be explained by movement of the IO closer to the recording electrode.

METHODS

We compared oVEMPs recorded with different gaze elevations to those recorded with constant gaze position but electrodes placed at increasing distance from the eyes. oVEMPs were recorded in ten healthy subjects using bursts of skull vibration.

RESULTS

oVEMP amplitude decreased more with decreasing gaze elevation (9 μV from 24° up to neutral) than with increasing electrode distance (2.7 μV from baseline to 6.4 mm; P<0.005). The oVEMP recorded with gaze 24° down had delayed latency (by 4.5 ms).

CONCLUSION

The effect of gaze elevation on the oVEMP cannot be explained by changes in position of the muscle alone and is likely mainly due to increased tonic contraction of the IO muscle in up-gaze. The oVEMP recorded in down-gaze (when the IO is inactivated, but the IR activated) likely originates in the adjacent IR muscle.

SIGNIFICANCE

Our results suggest that oVEMP amplitudes in extraocular muscles scale in response to changing tonic muscle activity.

Single motor unit activity in human extraocular muscles during the vestibulo-ocular reflex

Motor unit activity in human eye muscles during the vestibulo-ocular reflex (VOR) is not well understood, since the associated head and eye movements normally preclude single unit recordings. Therefore we recorded single motor unit activity following bursts of skull vibration and sound, two vestibular otolith stimuli that elicit only small head and eye movements. Inferior oblique (IO) and inferior rectus (IR) muscle activity was measured in healthy humans with concentric needle electrodes. Vibration elicited highly synchronous, short-latency bursts of motor unit activity in the IO (latency: 10.5 ms) and IR (14.5 ms) muscles. The activation patterns of the two muscles were similar, but reciprocal, with delayed activation of the IR muscle. Sound produced short-latency excitation of the IO muscle (13.3 ms) in the eye contralateral to the stimulus. Simultaneous needle and surface recordings identified the IO as the muscle of origin of the vestibular evoked myogenic potential (oVEMP) thus validating the physiological basis of this recently developed clinical test of otolith function. Single extraocular motor unit recordings provide a window into neural activity in humans that can normally only be examined using animal models and help identify the pathways of the translational VOR from otoliths to individual eye muscles.

Ocular vestibular evoked myogenic potentials produced by impulsive lateral acceleration in unilateral vestibular dysfunction

OBJECTIVE

To deduce the connectivity underlying ocular vestibular evoked myogenic potentials (OVEMPs) recorded from two sites and produced by lateral transmastoid stimulation in patients with unilateral vestibular dysfunction.

METHODS

OVEMPs were recorded using lateral impulsive stimuli delivered by a hand-held minishaker placed at the mastoid. Twelve patients were tested using the typical OVEMP recording montage placed inferior to the eyes. In a subset of 6 patients, recordings were also made using a lateral electrode montage. The majority of patients were tested following surgery for inner ear disease. Patient responses were compared to those in normal subjects under similar recording conditions.

RESULTS

For the inferior montage, regardless of which mastoid was stimulated, deficits were observed only from the eye opposite the affected ear. In contrast, OVEMPs recorded using the lateral electrode montage showed changes on both sides.

CONCLUSIONS

OVEMPs produced using lateral transmastoid stimulation and recorded from beneath the eyes are generated by a crossed vestibulo-ocular pathway while the projections underlying the lateral responses are likely to be bilateral.

SIGNIFICANCE

The vestibular-ocular connectivity underlying the OVEMPs recorded from inferior and lateral recording sites differs. For clinical use, the inferior recording site is the simplest to interpret.

Cervical and ocular vestibular evoked myogenic potentials are sensitive to stimulus phase

Sinusoidal forces with frequencies of 100 and 500 Hz and initial positive or negative polarities were delivered to the mastoids and Fz in normal subjects. We investigated whether the cVEMPs and oVEMPs evoked were sensitive to the polarity (phase) of vibration. With mastoid stimulation at 100 Hz, medial head acceleration produced cVEMPs with earlier latency (15.5 ms) than lateral acceleration (19.7 ms) and oVEMPs with later latency (13.8 ms) than lateral acceleration (10.6 ms). As the stimulus frequency increased, the difference in latency decreased, but was still present at 500 Hz. A similar pattern occurred following stimulation at Fz. Our results show that the initial direction of bone-conducted vibration affects both cVEMP and oVEMP properties even at relatively high frequencies.

Stochastic galvanic vestibular stimulation produces a small reduction in sway in Parkinson's disease

We investigated the effects of bicathodal stochastic galvanic vestibular stimulation (GVS) on body sway in normal subjects and in Parkinson's Disease (PD) patients. Twenty normal subjects and five PD patients were stimulated with four stimulus intensities between 0 and 0.5 mA and sway was measured in two stance conditions (on a compliant surface with either eyes open (EOCS) or closed (ECCS)). Subjects stood facing forward with their feet together on a force platform. Centre of pressure (CoP) displacement over 26 seconds was measured in the anteroposterior (AP) and mediolateral (ML) planes. GVS had no significant overall effect on sway in the normal subjects. In the patients a small (4.5%) significant decrease in sway was seen in the ECCS condition with low intensity (0.1 mA) stimulation (P=0.02). Similar changes were seen in the normal subjects. This work indicates that low intensities of stochastic GVS can reduce sway levels in PD patients for certain stance conditions.

Single trial detection of human vestibular evoked myogenic potentials is determined by signal-to-noise ratio

Vestibular reflexes in humans can be assessed by means of acoustically evoked responses of myogenic origin. For the vestibular-collic pathway this is termed the vestibular evoked myogenic potential (or VEMP) and for the vestibular-ocular pathway the ocular VEMP (or OVEMP). Usually VEMPs require an averaging process to obtain a clear response against the background myogenic activity, but depending on the combination of target reflex and stimulus mode, in some cases clear responses can be observed in single trials without averaging. We aimed to test whether this difference in detectability was simply related to signal-to-noise ratio (SNR), or a manifestation of some other difference in the reflex pathways. In four healthy subjects we recorded VEMPs and OVEMPs in response to 2-ms, 500-Hz sound pips and 10-ms, 100-Hz transmastoid vibrations at four intensity levels, and also determined thresholds. A plot of probability of detection P vs. SNR for all subjects and conditions fell onto a single sigmoid curve. When fitted by a logistic function after linearization a regression yielded an R(2) of 0.89 (n = 64, p < 0.001), with parameter estimates of mu = 2.9 and sigma = 2.0. Three patients with superior canal dehiscence, characterized by significantly lowered thresholds for sound-activated responses, exhibited a similar detection curve. We conclude that single trial detection of evoked myogenic potentials is a property mainly determined by SNR. Thus vestibular reflexes, differing in both their response magnitude and in their levels of myogenic activity by more than an order of magnitude, can be described by a single relationship when their magnitude is expressed relative to background activity, demonstrating the fundamental importance of the SNR.

Vestibular evoked myogenic potentials: past, present and future

Since the first description of sound-evoked short-latency myogenic reflexes recorded from neck muscles, vestibular evoked myogenic potentials (VEMPs) have become an important part of the neuro-otological test battery. VEMPs provide a means of assessing otolith function: stimulation of the vestibular system with air-conducted sound activates predominantly saccular afferents, while bone-conducted vibration activates a combination of saccular and utricular afferents. The conventional method for recording the VEMP involves measuring electromyographic (EMG) activity from surface electrodes placed over the tonically-activated sternocleidomastoid (SCM) muscles. The "cervical VEMP" (cVEMP) is thus a manifestation of the vestibulo-collic reflex. However, recent research has shown that VEMPs can also be recorded from the extraocular muscles using surface electrodes placed near the eyes. These "ocular VEMPs" (oVEMPs) are a manifestation of the vestibulo-ocular reflex. Here we describe the historical development and neurophysiological properties of the cVEMP and oVEMP and provide recommendations for recording both reflexes. While the cVEMP has documented diagnostic utility in many disorders affecting vestibular function, relatively little is known as yet about the clinical value of the oVEMP. We therefore outline the known cVEMP and oVEMP characteristics in common central and peripheral disorders encountered in neuro-otology clinics.

Vestibular evoked myogenic potentials evoked by brief interaural head acceleration: properties and possible origin

The vestibular system responds to head acceleration by producing compensatory reflexes in the eyes and postural muscles. In this study, we investigated the effect of brief interaural acceleration on the vestibular evoked myogenic potential (VEMP) in 10 normal subjects and 10 patients with bilateral (bVL) or unilateral vestibular loss (uVL). The stimuli were delivered with a handheld minishaker and tendon hammer over the mastoid and produced relatively pure interaural head acceleration with little rotation (mean peak acceleration: 0.14 g at 3.3 ms). VEMPs were recorded from the neck muscles and were characterized in normal subjects by a positive/negative potential ipsilateral to the stimulated side (peak latencies: 15.1 and 22.6 ms) and a positive response contralaterally (20.3 ms), which was sometimes preceded by a negativity (14.5 ms). These peaks were absent in patients with bVL, confirming their vestibular dependence. In the patients with uVL, medial acceleration of the intact ear produced bilateral responses, an initial positivity on the intact side, and a negativity on the affected side, whereas lateral acceleration produced only a late positivity on the intact side. As the acceleration was primarily in the horizontal plane, it is likely to have activated utricular receptors. Consistent with this, we found that VEMPs are very sensitive to the direction of head acceleration and have features consistent with the utriculocollic projections demonstrated in animals.

The effect of gaze direction on the ocular vestibular evoked myogenic potential produced by air-conducted sound

OBJECTIVE

To assess the effects of vertical and horizontal gaze, head rotation, body position, and vision on the ocular vestibular evoked myogenic potential (OVEMP) produced by air-conducted (AC) sound.

METHODS

Ten normal subjects were stimulated by 500 Hz 2 ms AC tone bursts at 136-142 dB peak SPL. OVEMPs were recorded from electrodes placed beneath the eyes. Angles of vertical gaze ranged from maximal downward to upward gaze in increments of 5-10 degrees . Horizontal gaze was measured during elevation and ranged from 20 degrees adduction to 20 degrees abduction.

RESULTS

Increasing vertical gaze increased OVEMP amplitude, especially for the contralateral eye (neutral vs maximal upward gaze; contra: 1.0 vs 2.6 microV; ipsi: 0.8 vs 0.9 microV; P<0.001). OVEMPs from the contralateral eye peaked significantly earlier in the upward gaze positions (contra: 9.2 ms; ipsi: 10.4 ms; P<0.001), but peaked later during downward gaze (contra: 14.2 ms; ipsi: 11.4 ms; P=0.014). There were small effects of horizontal gaze and supine body position, but no effects of head rotation or vision.

CONCLUSIONS

OVEMP amplitudes are strongly modulated by gaze position. Truncal position also affects OVEMP amplitude.

SIGNIFICANCE

This study quantifies the effect of gaze on the OVEMP and demonstrates the importance of controlling for gaze in clinical and experimental studies.

Tuning and sensitivity of the human vestibular system to low-frequency vibration

Mechanoreceptive hair-cells of the vertebrate inner ear have a remarkable sensitivity to displacement, whether excited by sound, whole-body acceleration or substrate-borne vibration. In response to seismic or substrate-borne vibration, thresholds for vestibular afferent fibre activation have been reported in anamniotes (fish and frogs) in the range -120 to -90 dB re 1g. In this article, we demonstrate for the first time that the human vestibular system is also extremely sensitive to low-frequency and infrasound vibrations by making use of a new technique for measuring vestibular activation, via the vestibulo-ocular reflex (VOR). We found a highly tuned response to whole-head vibration in the transmastoid plane with a best frequency of about 100 Hz. At the best frequency we obtained VOR responses at intensities of less than -70 dB re 1g, which was 15 dB lower than the threshold of hearing for bone-conducted sound in humans at this frequency. Given the likely synaptic attenuation of the VOR pathway, human receptor sensitivity is probably an order of magnitude lower, thus approaching the seismic sensitivity of the frog ear. These results extend our knowledge of vibration-sensitivity of vestibular afferents but also are remarkable as they indicate that the seismic sensitivity of the human vestibular system exceeds that of the cochlea for low-frequencies.