[Click-evoked myogenic potential as a new diagnostic tool for the vestibular disorders]

In accordance with Colebatch's method, click-evoked myogenic potential(VEMP: vestibular evoked myogenic potential) was studied to evaluate 11 healthy subjects and 24 patients with peripheral and central vestibular disorders such as sensorineural hearing loss, peripheral vestibular disorder, endolymphatic hydrops(Meniere disease), cerebellopontine (CP) angle tumor, and Wallenberg's syndrome. Surface electromyograms(EMG) were recorded from both sides of the sternocleidomastoid muscles, with a reference over the jugular notch. The EMG were averaged from 500 responses to 135 dB SPL, 3 c/s(0.1 ms) through one side of a headphone, with 115 dB masking noise in the other side. The average potentials were collected at 20 ms before the clicks to 80 ms afterwards. All healthy subjects showed typical biphasic complex responses(P 13-N 23-N 34-P 44) bilaterally by unilateral stimulation, predominantly on the ipsilateral side. The average latencies were as follows: P 13(13.3 ms +/- 2.1 SD); N 23(22.2 ms +/- 2.7 SD); N 34(32.2 ms +/- 3.1 SD); and P 44(43.6 ms +/- 3.1 SD). The average P 13-N 23 peak amplitude was 20.4 +/- 3.3 microV. In 5 cases of sensorineural hearing loss, in which pure tone audiograms showed thresholds higher than 80 dB, latencies of VEMP were within normal limits of the deaf side. In contrast, VEMP could not be evoked in the affected side in 4 patients with peripheral vestibular disorders or patients with 7 cerebello-pontine angle tumors. In 4 patients with endolymphatic hydrops, latencies of VEMP were within normal limits on the affected side. The P 13-N 23 peak amplitude, however, was remarkably enlarged after 500 ml of glycerol drip infusion(glycerol test). In 2 patients with Wallenberg's syndrome, the latency of P 13 was prolonged on the affected side. Thus, it is concluded that the present study would provide additional information about the vestibular function, especially the otolith function, and clinical usefulness of detecting both central and peripheral vestibular disorders.