Galvanic stimulation evokes short-latency EMG responses in sternocleidomastoid which are abolished by selective vestibular nerve section

Masseter Vestibular evoked myogenic potentials: A new tool to assess the vestibulomasseteric reflex pathway

Purpose

This review article provides the readers with an in-depth insight in understanding and interpreting various research literatures on the masseter vestibular evoked myogenic potentials (mVEMP). The article also reviews the contemporary researches involving the clinical applications of the mVEMP.

Conclusions

Masseter VEMP is an evolving yet clinically promising neuro-otology test tool that has recently gained more research interest and is considered an additional tool to diagnose various vestibular disorders. Masseter VEMP assesses the functional integrity of the acoustic-masseteric and vestibulo-masseteric reflex pathways. The mVEMP could be used as a complementary test to evaluate the same peripheral generator as the cervical VEMP but a different central pathway i.e., vestibulo-trigeminal pathway. Various research studies that have experimented on parameters such as the effect of different electrode montages (zygomatic vs mandibular configurations), stimulation rates, filter settings and stimuli used to evoke mVEMP have been discussed in this article that could assist in the optimization of a comprehensive clinical protocol. The latency and the amplitude of mVEMP waveforms serve as significant parameters in differentiating normals from those of the clinical populations. Along with the cVEMPs and oVEMPs, mVEMP might help diagnose brainstem lesions in REM Sleep behaviour disorders, Multiple Sclerosis and Parkinson's disease. However, further studies are required to probe in this area of research.

Vestibular dysfunction in pediatric patients with cochlear implantation: A systematic review and meta-analysis

Objective

Vestibular dysfunction may delay the achievement of balance and perception milestones in pediatric patients after cochlear implantation (CIM).

Methods

A strategic literature search was done following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched the PubMed, Medline, Embase, Web of Science, and Cochrane Library databases from inception to July 2022. Studies were included on the otoliths, semicircular canals, and balance function changes in children after CIM. Two reviewers independently assessed the level of evidence, methodological limitations, risk of bias, and characteristics of the cases. Matched pre- and postoperative vestibular functional test data, including ocular and cervical vestibular-evoked myogenic potential (oVEMP and cVEMP), caloric test, video head impulse test (vHIT), and Bruininks-Oseretsky Test 2 (BOT-2), were used to calculate the relative risk of vestibular disorders. Subgroup analyses were performed according to surgical approach, CIM device status, and etiology.

Results

Twenty studies that met the inclusion criteria were selected for the meta-analysis. We observed significant vestibular dysfunction in pediatric patients with CIM. The results showed a statistically significant increase in abnormal cVEMP response (RR = 2.20, 95% CI = 1.87, 2.58, P < 0.0001), abnormal oVEMP response (RR = 2.10, 95% CI = 1.50, 2.94, P < 0.0001), and abnormal caloric test results (RR = 1.62, 95% CI = 1.20, 2.19, P = 0.0018) after implantation. Statistically significant differences were not found in the vHIT test results of all three semicircular canals before and after the operation (P > 0.05). Regarding static and dynamic balance, we found significantly poorer BOT-2 scores in children with CIM than in the normal group (mean difference = −7.26, 95% CI = −10.82, −3.70, P < 0.0001).

Conclusion

The results showed that vestibular dysfunction might occur after CIM in pediatric patients. Some children experience difficulties with postural control and balance. Our results suggest that a comprehensive evaluation of vestibular function should be performed before and after CIM.

Potential vestibular pathway impairment in children with recurrent vertigo: An investigation through air-conducted sound and galvanic vestibular stimulation-triggered vestibular evoked myogenic potentials

Objective

This study aims to investigate the potential vestibular pathway impairment through vestibular evoked myogenic potentials (VEMPs) and to explore the pathophysiological significance of these instrument-based findings in children with recurrent vertigo.

Materials and methods

The clinical data of 21 children (mean age 4.67 ± 1.39 years) diagnosed as RVC who met the inclusion criteria of the Bárány Society and 29 healthy children (mean age 4.83 ± 1.34 years) enrolled as the control group from February 2021 to December 2021 were collected and analyzed retrospectively. All the subjects underwent both cervical VEMP (cVEMP) and ocular VEMP (oVEMP) triggered by air-conducted sound (ACS) and galvanic vestibular stimulation (GVS), respectively. The elicit rate, latency, and amplitude asymmetry ratio (AAR) of ACS-cVEMP, ACS-oVEMP, GVS-cVEMP, and GVS-oVEMP were analyzed.

Results

(1) The elicit rates of ACS-cVEMP and ACS-oVEMP were similar in the two groups (P > 0.05), as well as GVS-cVEMP and GVS-oVEMP (P > 0.05). (2) P1 and N1 latencies of ACS-cVEMP and GVS-cVEMP in the RVC group were longer than those in the control group (P < 0.05). (3) The N1 latency of ACS-oVEMP in the RVC group was shorter than that in the control group (P < 0.05), while there was no significant difference in the P1 latency of ACS-oVEMP (P > 0.05). The N1 and P1 latencies of GVS-oVEMP were not significantly different (P > 0.05). (4) There was no statistical difference in the AAR of ACS-cVEMP and GVS-cVEMP. Although there was an increased AAR of ACS-oVEMP in the RVC group (P < 0.05), the AAR was within the normal range. However, no statistical difference was found in the AAR of GVS-oVEMP in the two groups (P > 0.05).

Conclusion

The latencies of ACS-cVEMP and GVS-cVEMP in children with recurrent vertigo were significantly prolonged compared with those in healthy children, and there was no difference in elicit rates of ACS-cVEMP and GVS-cVEMP, suggesting that there might be potential impairment in the inferior vestibular nerve and the subsequent nerve conduction pathway in RVC.

Vestibular Extremely Low-Frequency Magnetic and Electric Stimulation Effects on Human Subjective Visual Vertical Perception

Electric fields from both extremely low‐frequency magnetic fields (ELF‐MF) and alternating current (AC) stimulations impact human neurophysiology. As the retinal photoreceptors, vestibular hair cells are graded potential cells and are sensitive to electric fields. Electrophosphene and magnetophosphene literature suggests different impacts of AC and ELF‐MF on the vestibular hair cells. Furthermore, while AC modulates the vestibular system more globally, lateral ELF‐MF stimulations could be more utricular specific. Therefore, to further address the impact of ELF‐MF‐induced electric fields on the human vestibular system and the potential differences with AC stimulations, we investigated the effects of both stimulation modalities on the perception of verticality using a subjective visual vertical (SVV) paradigm. For similar levels of SVV precision, the ELF‐MF condition required more time to adjust SVV, and SVV variability was higher with ELF‐MF than with AC vestibular‐specific stimulations. Yet, the differences between AC and ELF‐MF stimulations were small. Overall, this study highlights small differences between AC and ELF‐MF vestibular stimulations, underlines a potential utricular contribution, and has implications for international exposure guidelines and standards. © 2022 Bioelectromagnetics Society.

Retro-labyrinthine Lesion Site Detected by Galvanic Vestibular Stimulation Elicited Vestibular-evoked Myogenic Potentials in Patients with Auditory Neuropathy

OBJECTIVE

Auditory neuropathy (AN) is a unique pattern of hearing loss with preservation of hair cell function. The condition is characterized by the presence of otoacoustic emissions (OAE) or cochlear microphonic (CM) responses with severe abnormalities of the auditory brainstem response (ABR). The vestibular branches of the VIII cranial nerve and the structures innervated by it can also be affected. However, the precise lesion sites in the vestibular system are not well characterized in patients with AN.

METHODS

The air-conducted sound (ACS) vestibular-evoked myogenic potentials (VEMPs) and galvanic vestibular stimuli (GVS)-VEMPs were examined in 14 patients with AN.

RESULTS

On examination of VEMPs (n=14, 28 ears), the absent rates of ACS-cervical VEMP (cVEMP), ACS-ocular VEMP (oVEMP), GVS-cVEMP, GVS-oVEMP and caloric test were 92.9% (26/28), 85.7% (24/28), 67.9% (19/28), 53.6% (15/28), and 61.5% (8/13), respectively. Impaired functions of the saccule, inferior vestibular nerve, utricle, superior vestibular nerve, and horizontal semicircular canal were found in 25.0% (7/28), 67.9% (19/28), 32.1% (9/28), 53.6% (15/28) and 61.5% (8/13) patients, respectively. On comparing the elicited VEMPs parameters of AN patients with those of normal controls, both ACS-VEMPs and GVS-VEMPs showed abnormal results in AN patients (such as, lower presence rates, elevated thresholds, prolonged latencies, and decreased amplitudes).

CONCLUSION

The study suggested that patients with AN often have concomitant vestibular disorders. Retro-labyrinthine lesions were more frequently observed in this study. GVS-VEMPs combined with ACS-VEMPs may help identify the lesion sites and facilitate detection of areas of vestibular dysfunction in these patients.

The vestibulo-masseteric reflex and the acoustic-masseteric reflex: a reliability and responsiveness study in healthy subjects

The vestibulo-masseteric reflex (VMR or p11 wave), the acoustic-masseteric reflex (AMR or p1/n21 wave) and the mixed vestibulo-cochlear p11/n21 potential are responses of masseter muscles to sound that can be employed to evaluate brainstem function. This study was aimed at establishing the test-retest reliability and responsiveness of these reflex parameters according to the type of electrode configuration. Twenty-two healthy volunteers (M:F = 11:11; mean age 25.3 ± 5.2 years) participated in two testing sessions separated by one week. Zygomatic and mandibular montages were compared following unilateral and bilateral stimulations. For reliability purposes, intraclass correlation coefficient (ICC), coefficient of variation of the method error (CVME) and standard error of measurement (SEM) were calculated. The minimal detectable difference (MDD) was also determined as a measure of responsiveness. Both VMR (p11 wave) and AMR could be consistently evoked from test to retest, although the frequency rate was significantly higher (all p values ≤ 0.009) with zygomatic (VMR: 97.7-100%; AMR: 86.9-97.6%) than mandibular montage (VMR: 84.7-89.8%; AMR: 65.0-67.8%), with no significant differences between unilateral and bilateral stimulations. Good-to-excellent reliability and responsiveness (high ICC, low CV_ME, SEM and MDD scores) were detected for corrected amplitudes and peak latencies for all reflex responses, whereas raw amplitudes were associated to poor reliability. The reliability of the zygomatic montage proved superior to the mandibular montage for all reflex responses. Given their high test-retest consistency and capability to study different features of the reflex arch, both peak latencies and corrected amplitudes should be reported and considered in the interpretation of reflex testing results.

Audiological and Vestibular Findings in Subjects with MELAS Syndrome

OBJECTIVES

The mitochondrial DNA (mtDNA) point mutation m.3243A>G is known to express the following two syndromes among others: maternally inherited diabetes and deafness (MIDD) and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Sensorineural hearing loss (SNHL) is the most frequent symptom in individuals harboring the m.3243A>G mutation. However, dysfunction of the vestibular organs has been scarcely examined. Therefore, the present study aimed to study the impact of the m.3243A>G mutation on the inner ear.

MATERIALS AND METHODS

A total of 8 subjects harboring the blood-verified m.3243A>G mutation underwent thorough audiological and vestibular examinations, including tone and speech audiometry, video head impulse test (vHIT), ocular and cervical vestibular-evoked myogenic potential (oVEMP and cVEMP), and full otoneurological examination. The subjects also answered a Dizziness Handicap Inventory (DHI) questionnaire.

RESULTS

SNHL was identified in all the 8 subjects, with a mean pure-tone average-4 (PTA-4) of 59 dB. Speech discrimination score (n=7) ranged from 24% to 100% (mean 74%), and vHIT (n=42) detected pathology in nine lateral semicircular canals (SCCs), five posterior SCCs, and one anterior SCC, whereas three measurements were inconclusive. All oVEMPs (n=14 ears) were absent, nine cVEMPs were absent, and two were inconclusive. Based on the DHI scores, 6 subjects reported none to mild dizziness, 1 reported moderate, and 1 reported severe dizziness.

CONCLUSION

Our study population had pathological findings from every audiological and vestibular end organs. The results indicated that the pathological findings originated from within the end organs themselves and not within the superior and inferior vestibular or cochlear nerve.

A study on vestibular-evoked myogenic potentials via galvanic vestibular stimulation in normal people

Objectives

The aim of our study is to examine vestibular-evoked myogenic potentials (VEMPs) elicited by the galvanic vestibular stimulation in the sternocleidomastoid muscle (SCM) in healthy subjects for clinical applications of auditory neuropathy or vestibular neuropathy in the future.

Methods

We enrolled sixteen healthy subjects to record the average responses of SCM to galvanic vestibular stimulation (GVS) [current 3 mA; duration 1 ms] by electromyography (EMG). SPSS18.0 software was used to analyze the obtained data for mean and standard deviation.

Results

In all healthy subjects mastoid-forehead galvanic vestibular stimulation produced a positive-negative biphasic EMG responses on SCM ipsilateral to the cathodal electrode. The latency of p13 was 11.7 ± 3.0 ms. The latency of n23 was 17.8 ± 3.4 ms. The amplitude of p13-n23 was 147.0 ± 69.0 μV. The interaural asymmetry ratio (AR) of p13, n23 latency and the amplitude was respectively 0.12 ± 0.09, 0.08 ± 0.08 and 0.16 ± 0.10.

Discussions

Galvanic vestibular stimulation could elicit biphasic EMG responses from SCM via the vestibular nerve but not from the otolith organs. Galvanic stimulation together with air conducted sound (ACS) or bone conducted vibration (BCV) can elicit VEMPs and may enable the differentiation of retrolabyrinthine lesions from labyrinthine lesions in vestibular system.

Clinical use of skull tap vestibular evoked myogenic potentials for the diagnoses of the cerebellopontine angle tumor patients

Objective. To document our experiences using a new skull tapping induced Vestibular Evoked Myogenic Potentials (tap VEMPs) technique combined with standard Auditory Vestibular Evoked Myogenic Potentials (AC VEMPs) for advanced clinical assessment of cerebellopontine angle tumor (CPAT) patients. Design and Study Sample. Three patients were selected in order to highlight observations shown in a larger patient population and to show the variability of the findings. Both tap VEMPs and AC VEMPs were acquired from the sternocleidomastoid muscle (SCM) with EMG-based biofeedback and monitoring. Results. The usefulness of VEMPs was demonstrated, indicating the presence of a tumor and contributing additional information as to the involved nerve bundles in two out of the three cases. Conclusion. Due to the sensory organ dependency and related innervations differences, acquiring both AC VEMPs and tap VEMPs is likely to increase the probability of diagnosing CPATs and provide more information on the involved vestibular nerve bundles. This study demonstrates the feasibility of the possible expansion and combination of tap VEMPs and AC VEMPs techniques into a clinical diagnostic battery for advanced assessment of CPAT patients and its contribution as a guideline for the use of tap VEMPs in general.

Feasibility of simultaneous recording of cervical and ocular vestibular-evoked myogenic potentials via galvanic vestibular stimulation

CONCLUSION

Simultaneous galvanic vestibular stimulation (GVS)-cervical vestibular-evoked myogenic potential (cVEMP) and GVS-ocular (oVEMP) tests yielded similar information to that obtained in individual tests.

OBJECTIVE

This study compared the characteristic parameters of cVEMPs and oVEMPs via GVS between individual and simultaneous recording patterns in healthy and elderly subjects. Consequently, the effectiveness of simultaneous GVS-cVEMP and GVS-oVEMP tests was assessed.

METHODS

A total of 24 healthy and 16 elderly subjects were enrolled in this study. All participants underwent individual cVEMP, individual oVEMP, and simultaneous cVEMP and oVEMP testing via GVS mode in a random order. The response rates and characteristic parameters of cVEMPs and oVEMPs between individual and simultaneous tests, including latencies, intervals, and amplitudes, were measured.

RESULTS

The VEMP parameters, including latencies, intervals, and amplitudes, all demonstrated no significant differences between individual and simultaneous tests (p > 0.05, paired t test), either in healthy or elderly subjects. Pearson's correlation analyses also revealed significant positive correlations in all parameters between these two tests (p < 0.05).

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.

Effects of galvanic mastoid stimulation in seated human subjects

The vestibular responses evoked by transmastoid galvanic stimulation (GS) in the rectified soleus electromyogram (EMG) in freely standing human subjects disappear when seated. However, a GS-induced facilitation of the soleus monosynaptic (H and tendon jerk) reflex has been described in few experiments in subjects lying prone or seated. This study addresses the issue of whether this reflex facilitation while seated is of vestibulospinal origin. GS-induced responses in the soleus (modulation of the rectified ongoing EMG and of the monosynaptic reflexes) were compared in the same normal subjects while freely standing and sitting with back and head support. The polarity-dependent biphasic responses in the free-standing position were replaced by a non-polarity-dependent twofold facilitation while seated. The effects of GS were hardly detectable in the rectified ongoing voluntary EMG activity, weak for the H reflex, but large and constant for the tendon jerk. They were subject to habituation. Anesthesia of the skin beneath the GS electrodes markedly reduced the reflex facilitation, while a similar, although weaker, facilitation of the tendon jerk was observed when GS was replaced with purely cutaneous stimulation, a tap to the tendon of the sternomastoid muscle, or an auditory click. The stimulation polarity independence of the GS-induced reflex facilitation argues strongly against a vestibular response. However, the vestibular afferent volley, insufficient to produce a vestibular reflex response while seated, could summate with the GS-induced tactile or proprioceptive volley to produce a startle-like response responsible for the reflex facilitation.

Vestibular evoked myogenic potentials evoked by multichannel cochlear implant - influence of C levels

CONCLUSIONS

This study showed that vestibular evoked myogenic potentials (VEMPs) evoked by cochlear implant (CI), could be related to the comfortable level (C level), particularly in the channels that are closer to the apical turn of the cochlea.

OBJECTIVE

The purpose of this study was to investigate the correlation between VEMPs and C level of each channel.

SUBJECTS AND METHODS

We investigated 24 children who underwent cochlear implantation. VEMPs were recorded from the operated ears with the CI switched 'off' or 'on'. To investigate the correlation between VEMPs and C level, we selected 13 patients with Nucleus 24 (SPrint), and divided them into group A (normal VEMPs) and B (absence of VEMPs). In these children, all the 22 electrodes were active, and were mapped in the same frequency range for each channel.

RESULTS

Twenty children (83%) showed no VEMPs with the CI 'off'. Among them, 10 elicited VEMPs with the CI 'on', but the other 10 did not. In all channels, the mean C levels of CI were higher in group A than in group B. The p values in channels 1-12 were >0.10, in channels 13-16 were 0.06-0.09, and in channels 17-22 were 0.05-0.06, which were lower but not statistically significant.

Tone burst–galvanic ratio of vestibular evoked myogenic potential amplitudes: A new parameter of vestibular evoked myogenic potential?

OBJECTIVE

To clarify whether the ratio of tone burst vestibular evoked myogenic potential (VEMP) amplitude to galvanic (electric) VEMP amplitude can be a useful indicator of peripheral vestibular disorders, especially labyrinthine disorders.

METHODS

Twelve healthy volunteers and 12 patients with endolymphatic hydrops (EH) were enrolled in this study. VEMP was recorded using 500 Hz short tone bursts (135dBSPL, rise/fall time 1 ms, plateau time 2 ms) and galvanic stimulation (3 mA, 1 ms). Amplitudes of p13-n23 (tone burst) and p13g-n23g (galvanic) were corrected using background muscle activity. We defined the ratio of the corrected amplitude of p13-n23 to the corrected amplitude of p13g-n23g as TGratio.

RESULTS

The mean+/-SD of logarithmic value of TGratio (LTGratio) of healthy volunteers was 0.34+/-0.12. LTGratios in patients were 0.002+/-0.24 on the affected side and 0.34+/-0.14 on the unaffected side. LTGratio on the affected side of patients was significantly smaller than the ratio on the unaffected side and the ratio of healthy volunteers. Among the 12 patients with EH, 8 patients (66%) had significantly decreased LTGratio (smaller than mean-2SD of healthy volunteers).

CONCLUSIONS

Patients with EH had decreased ratio of tone burst VEMP amplitude to galvanic VEMP amplitude.

SIGNIFICANCE

TGratio (or LTGratio) could be a new promising parameter of VEMP as it can be calculated from results of one side.

Origin of sound-evoked EMG responses in human masseter muscles

Sound is a natural stimulus for both cochlear and saccular receptors. At high intensities it evokes in active masseter muscles of healthy subjects two overlapping reflexes: p11/n15 and p16/n21 waves, whose origin has not yet been demonstrated. Our purpose was to test which receptor in the inner ear is responsible for these reflexes. We compared masseter EMG responses induced in normal subjects (n = 9) by loud clicks (70-100 dB normal hearing level (NHL), 0.1 ms, 3 Hz) to those evoked in subjects with a selective lesion of the cochlea (n = 5), of the vestibule (n = 1) or with mixed cochlear-vestibular failure (n = 5). In controls, 100 dB clicks induced bilaterally, in the unrectified mean EMG (unrEMG), a clear p11 wave followed by a less clear n15 wave and a subsequent n21 wave. Lowering the intensity to 70 dB clicks abolished the p11/n15 wave, while a p16 wave appeared. Rectified mean EMG (rectEMG) showed, at all intensities, an inhibitory deflection corresponding to the p16/n21 wave in the unrEMG. Compared to controls, all deaf subjects had a normal p11 wave, together with more prominent n15 wave; however, the p16/n21 waves, and their corresponding inhibition in the rectEMG, were absent. The vestibular patient had bilaterally clear p11 waves only when 100 dB clicks were delivered bilaterally or to the unaffected ear. Stimulation of the affected ear induced only p16/n21 waves. Data from mixed patients were consistent with those of deaf and vestibular patients. We conclude that click-induced masseter p11/n15 waves are vestibular dependent, while p16/n21 waves depend on cochlear integrity.

Superficial siderosis causing retrolabyrinthine involvement in both cochlear and vestibular branches of the eighth cranial nerve

Although superficial siderosis (SS) has been clinically characterized as a combination of sensorineural hearing impairment, cerebellar ataxia and pyramidal signs, precise evaluation of the function of the eighth cranial nerve has rarely been reported. The purpose of this study was to evaluate the audiological and vestibular function. We present a patient with complaints of progressive bilateral hearing loss and gait difficulty. We evaluated the audiological and vestibular functions with auditory brainstem responses and vestibular evoked myogenic potentials (VEMPs) by clicks and galvanic stimuli. The patient showed linear hypointensities surrounding the brainstem, cerebellum and the eighth cranial nerve on T2-weighted MRI images, which is characteristic of SS. Auditory brainstem response showed only wave I in the right ear and no response in the left ear. Click VEMPs and galvanic VEMPs showed no response on either side. The results of a neuro-otological examination suggested that both audiological and vestibular dysfunction in the patient with SS is of retrolabyrinthine origin.

Vestibular-evoked myogenic potentials in cochlear implant children

CONCLUSIONS

Our results suggest that the sacculi of most children with cochlear implants can easily be damaged, as shown by the absence of vestibular-evoked myogenic potentials (VEMPs) in response to click stimuli. Also, in most of the children, the vestibular nerve was seemingly not stimulated by the cochlear implant. These results suggest that electrical stimulation at the C level can stimulate the cochlear nerve; however, this stimulation did not spread to the vestibular nerve in our children. In some children with Mondini dysplasia or vestibulocochlear nerve abnormality, the vestibular nerve was stimulated when the cochlear implant device was on, because of a VEMP response to electrical stimulation.

OBJECTIVE

To clarify the diagnostic value of VEMPs in cochlear implant patients.

MATERIAL AND METHODS

The click-evoked myogenic potentials of 12 children who underwent cochlear implantation surgery were investigated. The latency and amplitude of the VEMP responses were measured.

RESULTS

Before surgery, 6 of the 12 children showed normal VEMPs, 1 showed a decrease in the amplitude of VEMPs and five showed no VEMP response. After surgery, with the cochlear implant device off, 1 child showed a decreased VEMP and 11 showed no VEMPs. With the cochlear implant device on, four children showed VEMPs and eight did not.

Patient and normal three-dimensional eye-movement responses to maintained (DC) surface galvanic vestibular stimulation

HYPOTHESIS

That disease or dysfunction of vestibular end organs in human patients will reduce or eliminate the contribution of the affected end organs to the total eye-movement response to DC surface galvanic vestibular stimulation (GVS).

BACKGROUND

It was assumed that DC GVS (at current of 5 mA) stimulates all vestibular end organs, an assumption that is strongly supported by physiological evidence, including the activation of primary vestibular afferent neurons by galvanic stimulation. Previous studies also have described the oculomotor responses to vestibular activation. Stimulation of individual semicircular canals results in eye movements parallel to the plane of the stimulated canal, and stimulation of the utricular macula produces changes in ocular torsional position. It was also assumed that the total three-dimensional eye-movement response to GVS is the sum of the contributions of the oculomotor drive of all the vestibular end organs. If a particular vestibular end organ were to be diseased or dysfunctional, it was reasoned that its contribution to the GVS-induced oculomotor response would be reduced or absent and that patients thus affected would have a systematic difference in their GVS-induced oculomotor response compared with the response of normal healthy individuals.

METHODS

Three-dimensional video eye-movement recording was carried out in complete darkness on normal healthy subjects and patients with various types of vestibular dysfunction, as diagnosed by independent vestibular clinical tests. The eye-movement response to long-duration bilateral and unilateral surface GVS was measured.

RESULTS

The pattern of horizontal, vertical, and torsional eye velocity and eye position during GVS of patients independently diagnosed with bilateral vestibular dysfunction, unilateral vestibular dysfunction, CHARGE syndrome (semicircular canal hypoplasia), semicircular canal occlusion, or inferior vestibular neuritis differed systematically from the responses of normal healthy subjects in ways that corresponded to the expectations from the conceptual approach of the study.

CONCLUSION

The study reports the first data on the differences between the normal response to GVS and those of patients with a number of clinical vestibular conditions including unilateral vestibular loss, canal block, and vestibular neuritis. The GVS-induced eye-movement patterns of patients with vestibular dysfunction are consistent with the reduction or absence of oculomotor contribution from the end organs implicated in their particular disease condition.

Neuro-otologic findings in unilateral isolated narrow internal auditory meatus

OBJECTIVE

To report neuro-otologic findings concerning the four nerves in the internal auditory meatus (IAM) in patients with isolated congenitally narrow IAM and explore the implications regarding ontogeny of the nerves in the IAM.

DESIGN

Retrospective case series study.

SETTING

University hospital.

SUBJECTS

Five consecutive patients between 1997 and 2002 with unilateral isolated narrow IAM demonstrated by high-resolution computed tomography whose chief complaint was hearing loss (1 male and 4 females, 4 right sides and 1 left; age range 5-37 years, mean 20 years; IAM diameter at the porus: 26-33% of that on the normal side).

MAIN OUTCOME MEASURES

Functional studies concerning the VIIth cranial nerve and the three branches of the VIIIth cranial nerve.

RESULTS

In all ears, auditory brain stem responses were absent, the speech discrimination score was 0%, and otoacoustic emissions were absent or markedly reduced compared with those on the normal side. Caloric responses were absent in two ears, reduced in two ears, and normal in one ear. Galvanic body sway tests showed no responses in the two ears in which caloric responses were absent. Inferior vestibular nerve function was estimated as normal in all ears on the basis of vestibular evoked myogenic potential recordings. Facial nerve functions were normal in all patients.

CONCLUSIONS

In isolated congenital stenosis of IAM, dysfunction of each nerve in the IAM can occur independently. In the ontogeny of the VIIIth cranial nerve, the cochlear and superior vestibular nerves tended to be involved together, whereas the cochlear and inferior vestibular nerves appeared independent of each other.

Vestibular evoked myogenic potentials induced by intraoperative electrical stimulation of the human inferior vestibular nerve

Vestibular evoked myogenic potentials (VEMPs) can be recorded from sternocleidomastoid muscle (SCM) in clinical practice. The aim of the present study was to investigate VEMPs upon direct electrical stimulation of the human inferior vestibular nerve to evidence the vestibulocollic reflex arch and their saccular origin, respectively. Seven subjects were stimulated at the inferior (IVN) and superior (SVN) vestibular nerve. The EMG signals of the SCM were recorded. These recordings were compared to air- and bone-conduction evoked VEMPs with respect to latency and shape. All subjects showed normal VEMPs upon acoustic stimulation with a latency of 12.8+/-1.4 ms for P13, and 22.7+/-2.0 ms for the N23 pre-operatively. Upon direct electrical stimulation of the IVN, the mean latency of the positive peak was 9.1+/-2.2 and 13.2+/-2.3 ms for the negative one. No contralateral SCM response was found. Electrical stimulation of the SVN did not result in any EMG response of the SCM. The study shows experimental evidence of the vestibulocollic reflex by direct electrical stimulation of the human IVN for the first time. The method can be utilized to map VIIIth nerve subdivisions and to intraoperatively monitor IVN integrity in a real-time mode.

Vestibular testing by electrical stimulation in patients with unilateral vestibular deafferentation: galvanic evoked myogenic responses testing versus galvanic body sway testing

OBJECTIVE

To investigate the agreement of a lesion site as indicated by two different vestibular tests with electrical stimulation, galvanic body sway testing (GBST) and galvanic evoked myogenic responses (galvanic vestibular evoked myogenic potential; galvanic VEMP) testing, in patients with unilateral vestibular deafferentation.

METHODS

Nineteen patients with unilateral vestibular deafferentation were studied, and the criteria for patient selection were as follows: (1) absence of a caloric response to ice water on the affected side in a supine position, and (2) absence of VEMP to 95 dBnHL clicks on the affected side. We assessed the postural response of the subjects to long duration galvanic stimulation (1 mA, 5 s) by measuring the lateral displacement at the center of foot pressure with a cathode electrode on the forehead, and an anode electrode on the mastoid (GBST). We also recorded the electromyographic (EMG) activities of the sternocleidomastoid muscle (SCM) to short duration galvanic stimulation (3 mA, 1 ms) (galvanic VEMP) with a cathode electrode on the mastoid, and an anode electrode on the forehead.

RESULTS

In 18 of the 19 patients, the lesion site indicated by GBST was identical to that indicated by galvanic VEMP. Fourteen patients had abnormal results in both tests while 4 patients had normal results in both tests. One patient with acoustic neuroma had normal results in GBST but abnormal results in galvanic VEMP.

CONCLUSIONS

These results suggest that electrical stimulation in these two tests stimulates the same area of the peripheral vestibular afferent system, although the duration of stimulation was different, and that the estimate of the lesion site indicated by these tests in patients with complete or nearly complete unilateral vestibular damages is reliable.

SIGNIFICANCE

These results suggest that short-duration galvanic stimulation as well as long-duration galvanic stimulation stimulates the vestibular system at the same level.

A short latency vestibulomasseteric reflex evoked by electrical stimulation over the mastoid in healthy humans

We describe EMG responses recorded in active masseter muscles following unilateral and bilateral electrical vestibular stimulation (EVS, current pulses of 5 mA intensity, 2 ms duration, 3 Hz frequency). Averaged responses in unrectified masseter EMG induced by unilateral EVS were examined in 16 healthy subjects; effects induced by bilateral (transmastoid) stimulation were studied in 10 subjects. Results showed that unilateral as well as bilateral EVS induces bilaterally a clear biphasic response (onset latency ranging from 7.2 to 8.8 ms), that is of equal amplitude and latency contra- and ipsilateral to the stimulation site. In all subjects, unilateral cathodal stimulation induced a positive-negative response termed p11/n15 according to its mean peak latency; the anodal stimulation induced a response of opposite polarity (n11/p15) in 11/16 subjects. Cathodal responses were significantly larger than anodal responses. Bilateral stimulation induced a p11/n15 response significantly larger than that induced by the unilateral cathodal stimulation. Recordings from single motor units showed that responses to cathodal stimulation corresponded to a brief (2-4 ms) silent period in motor unit discharge rate. The magnitude of EVS-induced masseter response was linearly related to current intensity and scaled with the mean level of EMG activity. The size of the p11/n15 response was asymmetrically modulated when subjects were tilted on both sides; in contrast head rotation did not exert any influence. Control experiments excluded a possible role of cutaneous receptors in generating the masseter response. We conclude that transmastoid electrical stimulation evokes vestibulomasseteric reflexes in healthy humans at latencies consistent with a di-trisynaptic pathway.

Galvanic-evoked myogenic responses in patients with an absence of click-evoked vestibulo-collic reflexes

OBJECTIVES

To show that galvanic-evoked responses on the sternocleidomastoid muscle (SCM) are useful for differentiating labyrinthine lesions from retro-labyrinthine lesions in patients with an absence of click-evoked vestibulo-collic reflexes.

METHODS

We studied the average responses in the unrectified electromyographic (EMG) activities of the SCM to galvanic stimulation (3mA, 1ms). The cathodal electrode was on the mastoid, and the anodal electrode was on the forehead. Twenty-two healthy subjects and 28 patients with vestibular disorders were studied. All of the 28 patients showed the unilateral absence of vestibulo-collic reflexes evoked by 95dBnHL clicks on the affected side.

RESULTS

In healthy subjects mastoid-forehead galvanic stimulation produced a positive-negative biphasic EMG response at short latency on the SCM ipsilateral to the cathodal electrode. All patients with labyrinthine lesions showed biphasic EMG responses even in the affected side. In contrast, almost all patients with retro-labyrinthine lesions (16/18) showed no response or a decreased response on the affected side.

CONCLUSIONS

These results suggest that galvanic-evoked myogenic responses on the SCM may be useful in the differential diagnosis of labyrinthine lesions from retro-labyrinthine lesions in patients with an absence of vestibulo-collic reflexes evoked by clicks.

Vestibulocollic reflexes evoked by short-duration galvanic stimulation in man

1. Vestibular-dependent responses in leg muscles following transmastoid galvanic stimulation have been well characterized. Here we describe the properties of vestibulocollic responses evoked by transmastoid galvanic stimulation. 2. In twelve healthy human subjects we examined the averaged responses in unrectified sternocleidomastoid (SCM) EMG evoked by transmastoid stimulation using current pulses of 4 mA intensity and 2 ms duration. In ten subjects we also examined the effects of unilateral vestibular stimulation with the indifferent electrode at the vertex. In further experiments we studied the effects of different levels of background muscle activation, head position, current intensity and current duration. We compared these responses with click-evoked vestibulocollic responses in SCM. 3. A clearly defined biphasic response, beginning with a surface positivity, was recorded in the SCM ipsilateral to the side of cathode placement in all subjects. We refer to this as the p13/n23 [g] (galvanic) response, given the close similarity, in terms of waveform and latencies, to the previously described click-evoked p13/n23 vestibulocollic response. The amplitude of this response was linearly related to background muscle activation, current intensity and current duration, but independent of head position. Unilateral galvanic stimulation revealed the p13/n23 [g] response to be solely generated by the cathode. 4. A biphasic response beginning with a surface negativity (n12/p20 [g]) contralateral to the cathode was seen in all subjects and was generated by both the cathode contralaterally and the anode ipsilaterally. 5. Both the p13/n23 [g] and n12/p20 [g] potentials were abolished by selective vestibular nerve section and unaffected by severe sensorineural deafness. 6. We conclude that galvanic stimulation evokes short-latency vestibulocollic reflexes. These vestibulocollic reflexes have properties that are distinct from those described for galvanic-evoked vestibular reflexes in leg muscles, and which may be related to their differing physiological roles.