Diagnosis of vestibular dysfunction with electrical stimulation

Abstract

We report on the combined application of acoustic VEMP and electric VEMP for the diagnosis of vestibular dysfunction. For the recording of the acoustic VEMP, we used click (0.1 msec, 95 dBnHL) and 500-Hz short tone burst (rise/fall time 1 msec plateau time 2 msec, 95 dBnHL) stimuli. For the recording of the electric VEMP, we used 3-mA (1 msec) electrical stimulation. In the first part of the study, we applied this combined stimulation to patients who showed absent VEMP to click stimulation. Patients with labyrinthine lesions such as Meniere's disease showed normal electrical VEMP, although they showed no response to click stimulation. On the other hand, almost all patients with nerve lesions such as acoustic neuroma showed absent or decreased VEMP to electrical stimulation. These results suggest that electrical VEMP in patients with absent click-VEMP could be useful for the differentiation of labyrinthine lesions from nerve lesions. We applied this testing method to patients with vestibular neuritis and Ramsay Hunt syndrome. Patients with vestibular neuritis and Ramsay Hunt syndrome were classified in 2 groups. The majority had nerve lesions, while some patients had labyrinthine lesions. In the second part of the study, we applied the combined stimulation to patients with preserved acoustic VEMP. Then we calculated the acoustic-electric ratio of VEMP. In comparison with that in healthy subjects, patients with acoustic neuroma, and the unaffected sides of patients with Meniere's disease, the affected sides in patients with Meniere's disease showed a smaller acoustic-electric ratio of VEMP. These findings suggest hat the combined application of electrical VEMP and acoustic VEMP could be useful in the differentiation of labyrinthine lesions from nerve lesions even in patients with preserved acoustic VEMP.