[The characteristics of VEMP in patients with acoustic neuroma]

To establish the normal value of the vestibular evoked myogenic potential (VEMP), and to determine the characteristics of VEMP in patients with acoustic neuroma (AN) and to explore the significance of VEMP in diagnosis of AN.

Click-evoked VEMP was recorded with surface electrodes attached on the sternocleidomastoid muscle. Latencies and amplitudes of specific waveform of VEMP were measured. The hearing normal subjects including 26 males and 20 females were chosen to establish the normal value of VEMP. VEMP was investigated in 14 patients with AN who underwent surgery during the period of 2006-2007 as well as auditory brainstem response (ABR) and vestibular caloric test.

Of 46 subjects with normal hearing, VEMP was present in both ears in 43 subjects, absent in either ear in three subjects. The reducible rate is 93.5% (86/92). The nor-mal value obtained from 86 reducible ears were as follows (means +/- standard deviation): latency of p13 (11.86 +/- 2.11) ms, latency of n23 (18.57 +/- 2.19) ms, interval time between p13 and n23 (6.71 +/- 1.69) ms, amplitude of p13n23 (24.18 +/- 8.22) microV. Interaural variances in 43 subjects whose VEMP were available were as follows (means +/- standard deviation): /deltap13 (0.64 +/- 0.61) ms, /deltan23/(1.05 +/- 0.97) ms, interval time between /delta13n23/ (0.84 +/- 0.81) ms, amplitude ratio (max/min) 1.32 +/- 0. 37, interaural asymmetric ratio of VEMP 0.12 +/- 0.11. Of the 14 patients with AN, VEMP was absent on the affected side in eight patients, absent on either side in three patients, and present on the unaffected side in 11 patients. VEMP presented on the affected side in three patients was significantly prolonged in /deltapl3/ and /deltap13n23/.

Patients with AN characterized with VEMP could be useful in the diagnosis of AN combined together with other tests.