Glycerol pure tone audiometry and glycerol vestibular evoked myogenic potential: representing specific status of endolymphatic hydrops in the inner ear.

This prospective study attempts to explore the effect of glycerol on vestibular evoked myogenic potential (VEMP) in patients with definite unilateral Meniere's disease (MD) and to investigate whether the test reflects different pathologic states of endolymphatic hydrops (EH) in the inner ear by comparing the results of glycerol pure tone audiometry (PTA). Twenty-eight patients with definite unilateral MD were studied. As a control group, 11 patients with vestibular neuritis were selected. Sixteen ears of normal volunteers were enrolled to acquire normal range of the test. Each MD patient underwent glycerol testing measure with both conventional PTA and VEMP testing. Eleven vestibular neuritis patients also underwent glycerol-VEMP testing. The difference ratio was adopted to compare the changes in p1-n1 amplitude and latency of VEMP after the administration of glycerol (1.3 g/kg). Significant changes in the VEMP wave after the glycerol loading were seen in amplitude, but not in latency with MD patients. On the affected side, the amplitude of the p1-n1 biphasic wave significantly increased in 11 of 28 (39.3%) ears and decreased in 2 (7.1%) ears. On the unaffected side, 5 (17.9%) ears showed significant increase in amplitude. Significant changes in PTA were noted after administration of glycerol in 14 of 28 (50%) patients with MD. However, there was no statistically significant correlation between the test results. Glycerol administration had no significant effect on VEMP in patients with vestibular neuritis. The amplitude of VEMP in some patients with MD was increased, but the latency was not influenced by oral administration of glycerol. The severity of EH appears to vary in different parts of the inner ear. Glycerol-VEMP test results in patients with vestibular neuritis suggest that the VEMP reflects potential abnormality in the sacculocollic pathway, while glycerol-VEMP identifies the existence of EH in the saccule. VEMP and PTA after glycerol administration provide potential status of MD.