VESTIBULAR EVOKED MYOGENIC POTENTIALS IN PATIENTS WITH ACOUSTIC NEUROMAS

Background: To diagnose acoustic neuromas (ANs), the auditory brainste m response test and the caloric test have been used in addition to mag netic resonance imaging. The auditory brainstem response and the calor ic tests mainly reflect functions of the auditory pathway, ie, the coc hlear nerve and the superior vestibular nerve, respectively. Because t he vestibular evoked myogenic potential (VEMP) has been thought to ori ginate in the inferior vestibular nerve, we hypothesized that the VEMP could provide different information from the auditory brainstem respo nse and the caloric test and that it could be helpful in diagnosing AN s. In other words, we hypothesized that the VEMP could provide informa tion concerning inferior vestibular nerve involvement in patients with ANs. Objective: To find out if the VEMP could be useful in classifyin g ANs according to the involved nerves. Design: We reviewed preoperati ve clinical tests, including VEMPs, in 21 patients (8 men, 13 women) w ith ANs confirmed surgically and histopathologically, comparing them w ith VEMPs in 8 normal subjects (5 men, 3 women). Results: Whereas the first positive-negative peak of the VEMP, P13-N23, was ipsilaterally p resent on stimulation of the unaffected side in all patients with ANs and bath sides in all normal subjects, it was absent on the affected s ide in 15 patients (71%) and significantly decreased in amplitude in 2 patients (9%). Thus, 17 (80%) of the 21 patients showed abnormal VEMP s. Three patients had abnormal VEMPs although they had normal caloric responses. Three patients had abnormal caloric responses although they had normal VEMPs. Conclusion: These results suggest that the VEMP cou ld be useful for the diagnosis of AN, especially for classifying ANs a ccording to the involved nerves.