Normative study on 500 Hz tone burst vestibular evoked myogenic potential (VEMP) assessment

Abstract

The goal of the current study was to establish normative data on the various response indices of the VEMP assessment, when the response was elicited to 500 Hz tone burst stimuli. Eighteen adults with normally functioning vestibular systems participated in the current study. Responses were recorded on the sternocleidomastoid (SCM) muscles on each side of the necks of these subjects. Ipsilateral and contralateral recordings occurred for both sides of the neck, with the ipsilateral channel recording from the contracted SCM muscle on the same side of the monaural stimulation of 500 Hz tone burst stimuli, and the contralateral channel recording from the non-contracted SCM muscle on the opposite side to stimulation. The tonic EMG levels of the SCM muscle contraction were recorded during VEMP recordings for the ipsilaterally contracted SCM muscles. Two supra-threshold (i.e., 95 and 90 dB nHL) stimulus intensities were utilized to explore the characteristics of the robust VEMP response. Several response indices were measured from these supra-threshold VEMP responses. These included: (1) the absolute latency value of waves p13 and n23; (2) the peak-to-peak amplitude values of p13-n23; (3) interaural asymmetry ratio values for amplitude (4) laterality of the VEMP response; and (5) tonic EMG levels recorded during the supra-threshold VEMP recordings. The VEMP response was evaluated at lower stimulus intensities (i.e., 70-85 dB nHL) to determine each subject's VEMP threshold. The findings from the current study were, for the most part, found to be consistent with the VEMP literature. Latency values were stable across subjects for each of the VEMP components. Peak-to-peak amplitude values of p13-n23 were highly variable across our subjects. Interaural asymmetry ratio values were largely less than 30%, but in some cases were elevated and/or differed across stimulus intensities in the same subject. VEMP thresholds were consistent with the documented literature. The VEMP response was found to be largely dominant in the ipsilateral recording channel. Tonic EMG levels were found to be extremely variable across subjects with the natural contraction of SCM muscles. However, these tonic EMG levels were found to be very consistent across VEMP recordings in a single subject.