Vestibular evoked myogenic potentials in patients suffering from an unilateral acoustic neuroma: a study of 170 patients.

Abstract

To determine the value of investigating the vestibular evoked myogenic potentials (VEMP's) induced by clicks and 500 Hz short tone burst (STB) for the diagnosis of acoustic neuromas. We studied the average responses to 100dB clicks and 500 Hz STB in the ipsilateral sternomastoid muscle. Ninety-five healthy subjects and 170 patients suffering from a unilateral acoustic neuroma were included in that study. Caloric and audiometric tests results were also analyzed. Thirty-six/170 patients (21.2%) exhibited normal responses to clicks and to STB whereas 134/170 (78.8%) gave abnormally low or no responses. 78/170 (45.9%) showed no responses to both clicks and STB. In 56/170 patients (32.9%), VEMP's induced by high level clicks and STB were discordant: STB VEMP's were either normal (n=32) or low (n=24) in patients with an abnormal response to clicks (no response n=40 or low response n=16). In contrast, STB-induced VEMP's were always normal in cases of normal responses to clicks. No strong, systematic correlation could be found between saccular nerve dysfunction and either the degree of 4-8 kHz hearing loss or the extent of horizontal canalar impairment. These data indicate that high level clicks and STB provide complementary information about the functionality of the saccular nerve. Clicks are useful to detect a minor saccular nerve dysfunction. In cases in which there is no response to clicks, STB gives valuable information about a potential residual function of the saccular nerve.