RECORDING OF VESTIBULAR EVOKED MYOGENIC POTENTIALS

It has been shown recently that loud clicks evoke myogenic potentials in the tonically contracting sternocleidomastoid muscles. Studies have suggested that these potentials are of vestibular origin, especially of the saccule and inferior vestibular nerve. A pilot study was undertaken in our hospital to record vestibular evoked myogenic potentials (VEMP) for the first time in Iran. Eighteen healthy volunteers (32 ears) without history of otologic or vestibular disorders were subjected to the VEMP test. Twenty-one patients (26 ears) with unilateral (6 patients) and bilateral (5 patients) high frequency sensorineural hearing loss with unknown etiology, acoustic neuroma (1 patient), Meniere’s disease (4 patients) and unilateral low frequency sensorineural hearing loss without vestibular complaint (5 patients) were also enrolled in this study. VEMP response to clicks was obtained from 84.4% of ears of healthy subjects. These subjects demonstrated short latency waves to click stimuli during tonic neck flexor activation. Mean latencies of first positive (p13) and first negative (n23) potentials in healthy subjects were 12.45 ± 1.9 ms and 20.8 ± 3.5 ms, respectively. Median latencies of these two potentials were 12.1 and 19.3 ms, respectively. We could record VEMP in 5 patients with unilateral and all patients with high and low frequency sensorineural hearing loss without vestibular complaint. In the patient with acoustic neuroma VEMP was absent on the affected side. This technique may offer a new method to evaluate otolith and sacculocollic pathways in human.