The Effect of Various Modes of Excitation of Sterno-Cleido Mastoid Muscle on Vestibular Evoked Myogenic Potentials (VEMP)

Abstract

The Vestibular Evoked Myogenic Potential (VEMP) is an inhibitory potential recorded from the Sternocleidomastoid muscle (SCM) in response to loud sounds. VEMPs are short latency Electromyograms (EMG) that are evoked by higher-level acoustic stimuli and are recorded from surface electrodes over the tonically contracted SCM muscle. VEMP testing is considered to be easy, but there are a lot of technical pitfalls such as, operator pitfalls, assuring neck muscle activation, electrical artifact, mode of neck muscle activation, sound stimulus, electrode layout etc., Research in the area of VEMP have addressed the issues of subject variables and test parameters, but literature does not provide any suggestion to the clinicians about which method/mode of excitation of sternocleidomastoid muscle should be employed. So, as patient comfort and reliability of mode of excitation of sternocliedo mastoid are also the factors to be considered while testing, there is a need to study the effect of mode of excitation of SCM muscle on VEMP response. 25 normal male and 25 normal female subjects were tested for VEMP in three different body positions namely; Subject’s body rotated to one side for measurement of VEMP on the opposite side in sitting position, Subject’s body rotated to one side for measurement of VEMP on the opposite side while lying in supine position, subject pressing the Forehead against a soft surface. VEMP measures amplitude of P13-N23, latencies of P13, N23, response rate and wave morphology were analyzed along with the subjective rating on patient comfort in the three positions for all the subjects. Irrespective of gender VEMP measures such as latencies of P13, N23, amplitude of p13-n23, response rate and wave morphology were not affected by body position that is used to excite the sternocleidomastoid muscle during VEMP testing. But, the rating of comfortness was more to second position in males and to third position in females.