Abnormal Vestibular Evoked Myogenic Potentials Research Articles

Clinical and Diagnostic Characterization of Canal Dehiscence Syndrome

OBJECTIVE:: To identify otologic and audiologic characteristics of superior (and posterior) semicircular canal dehiscence (SCD). STUDY DESIGN:: Retrospective case review. SETTING:: Tertiary referral center. PATIENTS:: Sixty-five adult patients were evaluated for SCD; 26 of 65 (35 ears) had dehiscence. INTERVENTION(S):: Otologic examination, high-resolution computerized tomography (CT), air and bone audiometry, tympanometry, acoustic reflex, and vestibular evoked myogenic potential (VEMP). MAIN OUTCOME MEASURE(S):: Imaging demonstrating canal dehiscence, preferentially including Poschel and Stenvers reconstructions. Audiologic findings of pseudoconductive loss, intact ipsilateral stapedial reflex, and abnormally low VEMP thresholds. RESULTS:: The most common presenting complaints were autophony of voice and a "blocked ear" (94%), mimicking patulous eustachian tube, including relief with Valsalva or supine position (50%), but without autophony of nasal breathing. Pseudoconductive loss was found in 86% of dehiscence ears, and 60% (21 of 35) of these ears had better than 0-dB-hearing-loss bone conduction thresholds at 250 and/or 500 Hz. Acoustic reflex was present in 89%. Assuming CT as the criterion standard, VEMP resulted in 91.4% sensitivity and 95.8% specificity. One false-positive CT, with abnormal VEMP, resulted in surgical explorations negative for superior SCD but positive for posterior SCD. CONCLUSION:: Semicircular canal dehiscence may present with various symptoms such as autophony, ear blockage, and dizziness/vertigo. A combination of high-resolution CT and audiologic testing is recommended for diagnosis. Low-frequency conductive loss with better than 0 dB hearing level (HL) bone conduction threshold and normal tympanometry, with intact acoustic reflexes, are audiologic signs of SCD. Vestibular evoked myogenic potential is highly sensitive and specific for SCD, possibly better than CT.

Vestibular evoked myogenic potentials of undiagnosed dizziness

Objective Recording of vestibular evoked myogenic potentials (VEMP) can facilitate the evaluation of otolith function. The dizziness caused by otolith lesions is not completely understood. To clarify which symptoms of dizziness originate from the otolith organs, we examined the relationship between symptoms and VEMP results in patients with undiagnosed dizziness. Methods The subjects were 18 patients with undiagnosed dizziness aged less than 40 years who underwent VEMP examination. The VEMP results were evaluated using the interaural ratio of p13-n23 amplitude. Results Abnormal VEMP results were obtained in five of seven patients who experienced a sensation of falling ( p = 0.013), in none of the three patients who experienced a swaying sensation ( p > 0.05), and in one of eight patients who experienced a floating sensation ( p > 0.05). Five of six patients with abnormal VEMP results complained of disequilibrium lasting a few seconds. Conclusions Dizziness with a sensation of falling lasting for a few seconds was related to abnormal VEMP results, suggesting that it resulted from saccular dysfunction. VEMP examination may be considered a useful modality in the diagnosis of dizziness of unknown origin.

Vestibular click-evoked myogenic potentials: sensitivity and factors determining abnormality in patients with multiple sclerosis

Vestibular evoked myogenic potential (VEMP) assesses the sacculo-spinal pathway. The aim of our study was to examine sensitivity and factors determining abnormality of VEMP, indicative of brainstem dysfunction, in patients with multiple sclerosis (MS). Thirty healthy subjects and 30 MS patients were examined. All healthy subjects showed a normal biphasic response. Twelve of the 30 MS patients (40%) had abnormal recordings. There was a significant difference between MS patients and control subjects with respect to P13 latency (longer in the MS group) and P13-N23 amplitude (lower in the MS group). VEMP abnormalities were statistically significantly related to the presence of brainstem demyelinative lesions and a weaker correlation was found with disease duration. Clinical signs of vestibular dysfunction at any point during the course of the disease did not seem to affect the chances of obtaining abnormal VEMPs. Although the sensitivity of VEMP in detecting abnormality in MS patients is relatively low, its significance is evident in that it is the only electrophysiological method that is able to detect dysfunction in central vestibular pathways. Multiple Sclerosis 2007; 13: 193–198. http://msj.sagepub.com

Results and Sensitivity of a Comprehensive Audiological and Vestibular Work-Up in 100 Patients Presenting with a Vestibular Schwannoma

Purpose: To determine the results and sensitivity of a comprehensive audiological and vestibular work-up in 100 patients presenting with a vestibular schwannoma (VS). Material and Methods: One hundred consecutive cases of VS diagnosed from January 2004 to May 2005 were prospectively studied. Tumor size was classified according to the Koos classification and hearing was assessed according to the five-step Kanzaki classification. A comprehensive work-up was conducted in all patients, including complete tone and speech audiometry, brainstem evoked audiologic potentials (BEAP), vestibular evoked myogenic potentials (VEMP), and bithermal caloric testing using videonystagmography on both sides. BEAP responses were considered as normal or endocochlear when interwave intervals were normal, absent because of a poor hearing, or retrocochlear when interval between, wave 1 and 5 > 4.3 ms and/or when it differed > 0.25 ms between sides, or when no response was recorded when hearing was preserved. VEMP were considered as normal, absent, or diminished (amplitude 30%) or arreflexia (diminished > 80%). Results: Fifty-six females and 44 males were examined (mean age, 57.8 yrs). Left and right sides were equally affected. Vertigo, tinnitus, and hearing loss were the main presenting symptoms in 21%, 32%, and 68% of cases, respectively. Eighty-two percent were operated, 17% simply monitored, and 1% irradiated. The tumor was Stage 1, 2, 3, and 4 in 14%, 28%, 21%, and 37%, respectively. Hearing was class A in 9%, class B in 34%, class C in 14% and class E-D in 43% of the cases. Globally, BEAP showed a retrocochlear pattern in 64% of the cases and no response in 30%. Abnormal VEMP responses were observed in 94% of the cases. Caloric testing was abnormal in 61% and normal in 11%. Responses could not be analyzed in 28% of patients. Only one patient showed normal responses to the whole work-up (99% sensitivity); she suffered a very small intrameatal tumor and complained of contralateral audiological symptoms. Conclusion: An integrated neurotologic work-up is a powerful tool to diagnose all sizes of VS and is useful in predicting postoperative outcome. However, false-negative results remain possible in small intrameatal tumors (1%).

Clinical investigation on hypotensive patients with vertigo

The aim of this study was to investigate the characteristic of hypotensive patients with vertigo. Twenty hypotensive patients with rotatory vertigo, 15 hypotensive subjects without vertigo, and 15 mitral valve prolapse subjects without vertigo underwent a battery of tests including audiometry, electronystagmography (ENG), and vestibular evoked myogenic potential (VEMP) test. The abnormal rates in terms of audiometry, eye tracking, optokinetic nystagmus, visual suppression, and caloric tests were 15, 35, 35, 10, and 42% for the first group; 13, 20, 33, 0, and 0% for the second group; and 7, 13, 60, 0, and 3% for the third group, respectively. Comparison of the first group with the other two control groups revealed that significant difference existed only in the abnormality of caloric responses. Fifteen (75%) of 20 hypotensive patients with vertigo having abnormal ENG results, asymmetric caloric responses, or delayed VEMPs were attributed to vertigo of central origin, possibly from ischemic disorder. In contrast, five patients (25%) had neither central signs in ENG nor abnormal VEMPs, but showing bilateral normal or hyperactive caloric responses were classified as autonomic dysfunction. After 3 months of medication, all patients with autonomic dysfunction had their vertigo and autonomic symptoms subsided, whereas 27% of the patients with ischemic disorder had vertigo persisted, showing a significant difference. In conclusion, hypotensive patients with vertigo could be due to either direct autonomic dysfunction or ischemic disorder mediated by autonomic deficits.

Vestibular evoked myogenic potentials in benign paroxysmal positional vertigo and Meniere’s disease

The objective was to investigate vestibular evoked myogenic potentials (VEMP) in benign paroxysmal positional vertigo (BPPV) and Meniere's disease, and to determine if this type of testing is valuable for assessing the vestibular system. A prospective controlled clinical study was designed in a tertiary referral center setting. The 62 participants included 17 healthy controls and 45 other subjects selected from patients who presented with the complaint of vertigo (25 diagnosed with BPPV and 20 diagnosed with Meniere's disease). The main outcome measures of VEMP were recorded in all subjects and findings in each patient group were compared with control findings. The VEMP for the 30 affected ears in the 25 BPPV patients revealed prolonged latencies in eight ears and decreased amplitude in one ear (nine abnormal ears; 30% of total). The recordings for the 20 affected ears in the Meniere's disease patients revealed four ears with no response, six ears with prolonged latencies (ten abnormal ears; 50% of total). Only two (5.9%) of the 34 control ears had abnormal VEMP. The rate of VEMP abnormalities in the control ears was significantly lower than the corresponding rates in the affected BPPV ears and the affected Meniere's ears that were studied (P=0.012 and P<0.001, respectively). The results suggest that testing of VEMP is a promising method for diagnosing and following patients with BPPV paroxysmal positional vertigo and Meniere's disease. Further investigations with this method in other neurotologic pathologies might also be informative.

Function tests of the otolith or statolith system

This review aims to provide an overview of recent advances in tests to evaluate otolith function over the last 2 years. Over the last 2 years, many papers have focused on the application of the vestibular evoked myogenic potentials (VEMP). Several aspects are under survey: a search for optimal stimuli, search for normative data, search for which labyrinthine function losses and what kind of pathologies induce abnormal VEMPs. The review shows that some fundamental problems still have to be solved to improve reproducibility and to increase sensitivity. Other research and modelling is performed to find out how the brain distinguishes tilts from translations. Several papers support routine implementation of subjective visual vertical (SVV) measurements (in rest and during centrifugation) in the standard vestibular test battery. Interesting reports mention short latency vestibulo-ocular reflex induced by taps and short auditory stimuli. One report mentions the impact of otolith dysfunction upon spontaneous nystagmus and head shaking nystagmus. Although validation is still needed and in progress, the state of the art laboratory should consider the following tests for an evaluation of otolith function as relevant: slow tandem gait, VEMP, SVV during centrifugation.

Differentiating the cause of acute sensorineural hearing loss between Ménière's disease and sudden deafness

Conclusions. Most patients with Ménière's disease (MD) reveal abnormal vestibular-evoked myogenic potentials (VEMPs) and the recruitment phenomenon, whereas most sudden deafness patients display normal VEMPs without the recruitment phenomenon. We therefore recommend using both the recruitment phenomenon and VEMP testing as a diagnostic algorithm to differentiate between MD and sudden deafness as the cause of acute hearing loss. Objective. To recommend a diagnostic algorithm to differentiate between MD and sudden deafness as the cause of acute hearing loss. Material and methods. Between January 2002 and December 2003, 14 consecutive patients with “probable” MD who also had acute sensorineural hearing loss were enrolled in the study, together with another 14 age- and sex-matched patients with idiopathic sudden deafness. Each patient underwent a battery of audiovestibular function tests, including pure-tone audiometry, a stapedial reflex test, distortion-product otoacoustic emissions (DPOAEs), electronystagmography and a VEMP test. All patients were followed for at least 12 months after presentation. Results. Significant differences were found between MD and sudden deafness in terms of the recruitment phenomenon (86% and 21% of cases, respectively) and abnormal VEMP responses (71% and 21% of cases, respectively). However, the diseases did not differ significantly in terms of abnormal DPOAEs or caloric test results.

Abnormal Vestibular Evoked Myogenic Potentials in the Presence of Normal Caloric Responses

Combined use of vestibular evoked myogenic potential (VEMP) and caloric response testing has enabled us to examine the function of the inferior and superior vestibular nerves separately. Although results of VEMP testing and caloric response testing have been reported for many diseases, a clinical entity showing abnormal VEMP responses but normal caloric test responses has rarely been reported. The aim of the study was to investigate clinical features of diseases showing abnormal VEMP responses with normal caloric test responses. Retrospective. University hospital. Eight hundred eleven patients with balance problems who had undergone both caloric response and VEMP testing were included in the study. The amplitudes and latencies of the first positive-negative peak of the VEMP (p13-n23) were measured. Forty of the 811 patients (5%) were found to have abnormal VEMP responses with normal caloric test responses. Clinical diagnoses of these patients were Ménière's disease (n = 12), acoustic neuroma (n = 8), sudden deafness with vertigo (n = 6), and other diseases (n = 6). Eight patients could not be diagnosed as having a disease already recognized. Clinical manifestations of these eight patients were rotatory vertigo in six patients and non-rotatory dizziness in two. None of these patients showed abnormalities other than VEMP responses on neurologic or neurotologic examinations. Apart from Ménière's disease, acoustic neuroma, and sudden deafness with vertigo, which are already known as diseases with abnormal VEMP responses but normal caloric test responses, some patients might be diagnosed as having a disease that involves only the inferior vestibular nerve region.

Changes in Vestibular Evoked Myogenic Potentials after Meniere Attacks

The aim of this study was to apply videonystagmography (VNG) and vestibular evoked myogenic potential (VEMP) tests to patients with Meniere attacks, to explore the mechanics of where saccular disorders may affect the semicircular canals. From January 2001 to December 2003, 12 consecutive patients with unilateral definite Meniere's disease with vertiginous attacks underwent VNG for recording spontaneous nystagmus, as well as VEMP tests. At the very beginning of the Meniere attack, the spontaneous nystagmus beat toward the lesion side in 5 patients (42%) and toward the healthy side in 7 patients (58%). Twenty-four hours later, only 6 patients (50%) showed spontaneous nystagmus beating toward the healthy side. Nevertheless, spontaneous nystagmus subsided in all patients within 48 hours. The VEMP test was performed within 24 hours of a Meniere attack; the VEMPs were normal in 4 patients and abnormal in 8 patients (67%). After 48 hours, 4 patients with initially abnormal VEMPs had resolution and return to normal VEMPs, and the other 4 patients still had absent VEMPs. Most patients (67%) with Meniere attacks revealed abnormal VEMPs, indicating that the saccule participates in a Meniere attack. This is an important idea that stimulates consideration of the mechanism of Meniere attacks.

Vestibular Evoked Myogenic Potentials in Acute Low‐Tone Sensorineural Hearing Loss

It was the authors' premise that the vestibular evoked myogenic potential (VEMP) test may be used to differentiate acute low-tone hearing loss (ALHL) from Meniere's disease with low-tone HL. Prospective study. From January 2000 to December 2002, consecutive 12 patients with ALHL and another 12 patients with definite Meniere's disease with low-tone HL were enrolled in this study. All patients underwent audiometry and VEMP test, before and after treatment with isosorbide for 3 consecutive months. Before treatment, 12 patients with ALHL revealed normal VEMPs (11, 92%) and augmented VEMPs (1). After treatment, 11 (92%) patients had resolved to normal hearing within 3 days. One year later, two (17%) patients progressed to Meniere's disease. In comparison with Meniere's disease, 6 (50%) of 12 patients showed normal VEMPs before treatment, and 7 (58%) patients had their hearing improved 3 months after treatment. Comparison of VEMP responses or hearing outcome between both groups exhibited significant differences. Most patients with ALHL reveal normal VEMPs throughout the episode, indicating that the saccule is spared. In contrast, 50% of Meniere's disease patients with low-tone HL demonstrate abnormal VEMPs, showing a significant difference. Therefore, the VEMP test can be used to differentiate ALHL from Meniere's disease with low-tone HL.

Vestibular evoked myogenic potentials in response to skull taps for patients with vestibular neuritis

In recent years it has been demonstrated that loud clicks generate short latency vestibular evoked myogenic potentials (VEMP). It has also been demonstrated that skull tap stimulation evokes similar VEMP. In the present study, the differences between the click-induced and the skull-tap induced VEMP were studied in 18 patients at onset of vestibular neuritis. Gentle skull taps were delivered manually above each ear on the side of the skull and on the forehead midline. The muscular responses were recorded over both sternocleidomastoid muscles using skin electrodes. Abnormal skull tap VEMP were found in the majority of the patients (10/18, 56%). However, only 4/18 (22%) showed asymmetry in the click-induced VEMP. The high percentage of abnormal skull tap VEMP might suggest that this response is not only dependent on the inferior division of the vestibular nerve, because the inferior division of this nerve is usually spared in vestibular neuritis. Moreover, the patients with abnormal skull tap VEMP differed from those with normal VEMP in their settings of the subjective visual horizontal with static head tilt in the roll plane. This might suggest that skull tap VEMP are (also) related to utricular function.

Vestibular evoked myogenic potentials in delayed endolymphatic hydrops.

Vestibular evoked myogenic potential (VEMP) has become an established test to explore the sacculo-collic reflex. The study aims to investigate the VEMPs in cases of delayed endolymphatic hydrops because greatly dilated saccule was observed in histopathological specimens of delayed endolymphatic hydrops. Prospective study. Twenty patients with delayed endolymphatic hydrops were subjected to pure-tone audiometry, caloric testing, and VEMP test. Delayed VEMP was defined as the latency of peak I exceeding 22.6 milliseconds or of peak II exceeding 33.1 milliseconds. Interaural amplitude difference over the sum of amplitudes of both ears was measured, and when the ratio exceeded 0.36, it was identified as augmented VEMP or depressed VEMP depending on whether the amplitude of the lesioned side was greater or less than the opposite side. The VEMP test revealed that 9 patients (45%) were normal, 6 (30%) exhibited absent VEMPs, and 5 (25%) displayed abnormal VEMPs, including delayed VEMPs in 2, depressed VEMPs in 2, and augmented VEMPs in 1. The caloric test indicated that 9 (47%) of the 19 ears exhibited normal caloric response, whereas 10 ears displayed abnormal caloric responses including canal paresis in 8 and absent caloric response in 2. Six ears had preserved both the caloric response and the VEMPs, whereas no ear demonstrated both absent caloric response and absent VEMPs. The residual caloric as well as saccular functions after ear insult may determine whether delayed endolymphatic hydrops will occur. These findings suggest that patients with sudden deafness or juvenile unilateral total deafness should undergo caloric testing and VEMP test to predict the occurrence of delayed endolymphatic hydrops in the future.

Vestibular Evoked Myogenic Potentials in Patients with Spinocerebellar Degeneration

To estimate vestibulo-collic reflexes in patients with spinocerebellar degeneration (SCD), vestibular evoked myogenic potentials (VEMPs) were recorded in 16 patients with SCD and in 9 normal subjects. The patients with SCD were classified into three groups: those with olivo-ponto-cerebellar ataxia (OPCA; n=10); those with cortical cerebellar atrophy (CCA; n=3); and those with Machado-Joseph disease (MJD; n=3). While all of the patients with OPCA and CCA showed biphasic responses (p13-n23), 2 of the 3 patients with MJD showed abnormal VEMPs bilaterally. Three sides in these 2 patients showed an absence of VEMPs, and one side showed a remarkably delayed p13. These two patients showed little response in caloric tests. These results suggest that the vestibulo-collic reflex as well as the vestibulo-ocular reflex could be damaged in MJD patients but preserved in OPCA and CCA patients.

Vestibular evoked myogenic potentials in acoustic tumor patients with normal auditory brainstem responses.

In order to clarify the utility of the vestibular evoked myogenic potential (VEMP) in detecting acoustic tumors, we report two patients who were found to have normal auditory brainstem responses (ABRs) and abnormal VEMPs. To record VEMPs, electromyographic responses to brief loud clicks (0.1 ms at 95 dBnHL) were amplified and averaged on the sternocleidomastoid muscle ipsilateral to the stimulated side. The stimulation rate was 5 Hz and the analysis time 50 ms. The first case was a 54-year-old woman in whom VEMPs were absent on the affected side while caloric tests and ABRs were normal. The second case was a 58-year-old woman whose VEMPs were absent on the affected side while caloric tests revealed a 22% canal paresis and normal ABRs. These results and previous studies suggested that the VEMP could reflect a function different from those evaluated by the ABR or the caloric test. We concluded that the VEMP can provide useful information in diagnosing acoustic tumors.

Ｇａｌｖａｎｉｃ ｂｏｄｙ ｓｗａｙ ｔｅｓｔ異常症例における前庭性頚筋電位（ＶＥＭＰ）

In order to clarify whether the galvanic body sway test (GBST) is useful for differential diagnosis of lesions in patients with absent vestibular evoked myogenic potentials (VEMP), clinical records of patients with absent GBST were reviewed. Patients were 4 men and 10 women. Their ages ranged from 32 to 81. Diagnoses were vestibular neuritis in 6 patients, acoustic neuroma in 7 patients, and temporal bone fracture in one patient. GBST were performed using a stabilometer. As stimulation, 0.6 mA electrical stimuli were presented for 3 seconds. Electrodes were placed on the mastoid and the forehead. For recording VEMPs, electrodes were placed on the upper half of the sternocleidomastoid muscle and the lateral end of the upper sternum. As stimulation, 95 dBnHL clicks were presented at the rate of 5 Hz. Signals were amplified and bandpass-filtered (20-2000 Hz). One hundred responses were averaged. Whereas all of the 14 patients showed abnormal caloric responses, 4 patients (29%) showed normal VEMPs. These results suggested that GBST is not always useful for differential diag-nosis of retro-labyrinthine lesions from labyrinthine lesions in patients with abnormal VEMPs, while GBST could be useful for differential diagnosis in patients with abnormal caloric responses. We should establish other clinical testing for differential diagnosis of retro-labyrinthine lesions from labyrinthine lesions in patients with abnormal VEMPs.

Vestibular evoked myogenic potentials in patients with acoustic neuromas.

To diagnose acoustic neuromas (ANs), the auditory brainstem response test and the caloric test have been used in addition to magnetic resonance imaging. The auditory brainstem response and the caloric tests mainly reflect functions of the auditory pathway, ie, the cochlear nerve and the superior vestibular nerve, respectively. Because the vestibular evoked myogenic potential (VEMP) has been thought to originate in the inferior vestibular nerve, we hypothesized that the VEMP could provide different information from the auditory brainstem response and the caloric test and that it could be helpful in diagnosing ANs. In other words, we hypothesized that the VEMP could provide information concerning inferior vestibular nerve involvement in patients with ANs. To find out if the VEMP could be useful in classifying ANs according to the involved nerves. We reviewed preoperative clinical tests, including VEMPs, in 21 patients (8 men, 13 women) with ANs confirmed surgically and histopathologically, comparing them with VEMPs in 8 normal subjects (5 men, 3 women). Whereas the first positive-negative peak of the VEMP, P13-N23, was ipsilaterally present on stimulation of the unaffected side in all patients with ANs and both sides in all normal subjects, it was absent on the affected side in 15 patients (71%) and significantly decreased in amplitude in 2 patients (9%). Thus, 17 (80%) of the 21 patients showed abnormal VEMPs. Three patients had abnormal VEMPs although they had normal caloric responses. Three patients had abnormal caloric responses although they had normal VEMPs. These results suggest that the VEMP could be useful for the diagnosis of AN, especially for classifying ANs according to the involved nerves.

タッピング法による頚筋電位 クリック音による前庭性頚筋電位との比較検討

Vestibular evoked myogenic potentials (VEMP) by tapping the head and by clicks were studied in 6 normal subjects (4 males and 2 females, age : 26 to 38 years old) and 11 patients with cochleo-vestibular disorders (4 males and 7 females, age : 22 to 66 years old). Diagnoses were acoustic neuroma in 5 patients, vestibular neuronitis in 2 patients, low tone sensorineural hearing loss in 2 patients, Meniere's disease in one patient and sensorineural hearing loss in one patient. All of the normal subjects had biphasic responses (p13-n23) to tapping the head as well as to clicks. We evaluated VEMPs in patients with cochleo-vestibular disorders with reference to the presence of p13-n23, amplitude ratio of p13-n23, and interaural latency differences of p13 and n23. In patients with cochleo-vestibular disorders, VEMPs by clicks were absent in 7 patients, decreased in amplitude in 2 patients and normal in 2 patients. VEMPs by tapping were absent in 3 patients, prolonged in latency of p13 in 5 patients and normal in 3 patients. Concerning differentiation of normal VEMPs from abnormal VEMPs, 10 of 11 patients showed the same VEMPs by tapping as by clicks. As long as interaural latency differences are included as parameters of evaluation, VEMP by tapping is a useful substitution for VEMP by clicks.

小脳橋角部腫よう３症例におけるクリック音刺激による前庭性頚筋電位

Vestibular evoked myogenic potentials (VEMPs) have been reported as a clinical test on the vestibular system. We examined VEMPs in three patients with cerebel-lopontine angle tumors (CPAT) and in six normal subjects. To record VEMPs, a positive electrode was placed on the sternocleidomastoid muscle (SCM), and a reference electrode was placed on the lateral end of the upper sternum. During the recording, subjects were instructed to rotate their heads in the direction opposite to the stimulated side to activate the SCM. Electromyographic signals from each side were amplified and bandpass filtered (20-2000 Hz). Clicks (0.1 ms, 95 dBnHL) were presented through a headphone. The stimulation rate was 5 Hz, the analysis time was 50 ms. The responses to 200 stimuli were averaged. The patients with CPAT also underwent pure tone audiometry (PTA), ABR, and caloric tests. In all normal subjects, VEMPs, a positive peak at about 13 ms and a negative peak at about 23 ms after presentation of click were recorded on the SCM ipsilateral to the stimulated side. All patients with CPAT showed abnormal VEMPs on the affected side. Two patients showed absence of VEMPs although caloric responses were present. One patient showed decreased VEMPs, but his caloric responses were normal. VEMPs in this patient disappeared after neurosurgery, although pure tone hearing and ABRs were not changed. Results of our study and a review of the literature suggested that VEMPs could reflect a function different from those of ABRs and caloric responses.