Vestibular Evoked Myogenic Potentials(VEMP):Clinical Setting And Clinical Application

Objectives:Vestibular evoked myogenic potentials (VEMP) is a clinical test recording the myogenic responses from vestibular organ stimulated by click sound. In clinical practice it was noticed that the variation of the VEMP amplitudes were dependent on the acoustic stimulation and the contraction of the sternocleidomastoid muscle, which made it difficult to interpret the results. This had limited the clinical application of the technique. The present study is to use a designed technique to monitor and control the neck muscle during measurement which would help to achieve the stability and reproducibility of measured VEMP amplitudes.Methods:The measurements were carried on19normal hearing subjects (male:12; mean age:34.0±7.7years) and16patients with otologic diseases (9otosclerosis and7acoustic neuroma). A pressure feedback device composed of a rubble bulb and a pressure gauge was designed to facilitate the subjects to monitor and control the neck muscle contraction during the measurement. Subjects were instructed to position their chins on the rubber bulb and using the neck flexors to maintain a pressure of120mm Hg during the measurement. The latencies of P13and N23as well as the P13-N23amplitudes were recorded. In nine subjects, the reproducibility of the technique was tested weekly in three consecutive weeks.Results:In normal subjects, the average (±SD) latency of P13was13.97±1.33ms, and was24.03±1.79ms of N23. The average amplitude was66.89±44.1μV. There was no significant difference between right and left ears in P13and N23latencies. The right/left ear AR%was15.8±13.34%and was no significant difference. However, the absolute values of the VEMP amplitudes in the group varied from35.57to198.57μV.7out of9patients with otosclerosis had VEMP absent on lesion side and the depression of VEMPs was noticed on3out of7cases of acoustic neuroma (AR%>40). In nine subjects, the average interclass correlation coefficient (ICC) were0.97in amplitude,0.8in P13latency and0.93in N23latency in three consecutive weekly measurements.Conclusions:1. When utilizing the technique introduced in the study, the subjects were able to monitor and control the neck muscle contraction level at120mmHg fed back by the pressure gauge. It was demonstrated by the study that this technique was simple and practical with the stable and reproducible VEMP amplitudes.2. Because of the variation of the VEMP amplitudes among subjects, it was hard to work out the reference values of the VEMP amplitudes in normal subjects. However, when employing the present technique, it was possible to compare the results from different measurements on the same subject.3. As a non-invasive technique in assessing the vestibular function, VEMP had some clinical values in the diagnosis of ear lesions such as Meniere disease and superior semicircular canal dehiscence.