Myogenic Vestibular-Evoked Potentials in Normal Subjects: A Comparison Between Responses Obtained from Sternomastoid and Trapezius Muscles

Abstract

Brief intense clicks cause short latency microcontraction of cervical muscles. Several studies have supported the hypothesis that these microcontractions are of vestibular origin. Averaging these muscular responses enables us to obtain myogenic vestibular evoked potential (MVEP). The receptor of these responses is thought to be the saccule, afferent pathways being the vestibular nerve and efferent pathways the vestibulospinal tract. However, discrepancies are reported with regard to results obtained in healthy subjects: some authors obtained symmetrical response to monaural clicks whereas others obtained responses of greater amplitude on the muscle ispilateral to stimulation. These discrepancies may be due to the presence of different recording sites (inion, sternomastoid or trapezius muscles). The aim of this study was to clarify MVEP results in healthy subjects, using a simple non-traumatic method, and to compare the results obtained on sternomastoid (SM) and trapezius muscles (TRP). Sixteen normal hearing healthy subjects were involved. Latencies and amplitude of both SM and TRP muscle were reproducible in the same subject. Patterns of response were similar to those obtained in previous studies. Following binaural and monaural stimulations, latencies of MVEP were symmetrical on both muscles and amplitudes tended to be greater on muscles contralateral to stimulation, which conflicts with previous results in the literature. Whatever the type of stimulation, latencies of responses obtained on SM were significantly shorter (mean = -3.8 ms), and amplitudes lower (mean = -7.1 microV), than those obtained on TRP. Binaural stimulation resulted in responses of greater amplitude compared to monaural (mean = 0.45 microV). Given the intrasubject reproducibility of the responses, these methods allow MEVP to be recorded in a standardized and reproducible way.

Potenciais miogênicos evocados vestibulares: metodologias de registro em homens e cobaias

“…In the literature 2,8,13,14,17,19,20,25,27,28,34 , it is reported that the trapezius and the sternocleidomastoid muscles allow a better recording of VEMPs, because it is easier to place the leads and there is higher muscle action potential triggering, necessary to obtain this potential, and its recording in the other anatomical regions is practically unfeasible.…”

“…In most studies 2,[8][9][10][11][14][15][16]18,19,24,[28][29][30][31] , the stimuli were averaged by means of ear phones instead of the bone vibrators and the intensities were, usually, above 90 dBHL.…”

“…The recording is done by means of averaging or adding, and the parameters used in most studies are equal to or higher than 200 stimuli 2,[8][9][10]14,17,20,26,27,30,31 . In general, the higher the number of stimuli and the lower the shooting rate (number of stimuli per second), the better the recording quality.…”

“…VEMPs must be recorded in a silent room (there is no need to be sound proof) 8,21,10 , under mild and uniform temperature, and the patient must be sitting in a comfortable chair or laying down on a bed. The patient and/or family members must be educated about the procedures carried out during the test in order to avoid possible physical or emotional stress, which can interfere in the recordings.…”

“…Currently, stimuli above 90 dBHL are used 2,[8][9][10][11][14][15][16]18,19,24,[28][29][30][31] . However, in many studies, the threshold is surveyed by means of stimuli of different intensities (with ascending or descending techniques) until the lowest stimulus intensity capable of triggering a response is found 2,21,25,32 .…”