Vibration-induced nystagmus in patients with unilateral peripheral vestibular disorders.

This study was done to clarify the clinical significance of vibration-induced nystagmus (VIN) and to calculate the sensitivity and the specificity of the vibration test. One hundred and twelve patients with unilateral peripheral vestibular disorders and thirty normal subjects were enrolled into this study. However, patients with spontaneous nystagmus were excluded. Vibration stimuli (approximately 100 Hz) were presented to the mastoids and the forehead. Patients and normal subjects also underwent head shaking nystagmus (HSN) test and caloric testing. Among the 112 patients, 91(81 %) showed VIN which were mainly horizontal. VIN was more frequently elicited on the mastoids than on the forehead. In the majority of patients (76 cases), the direction of VIN was toward the healthy side, whereas patients with Meniere's disease (15 cases), showed nystagmus toward the affected side. None of 30 normal subjects showed VIN. Whereas HSN was found in 70 (63 %) patients and 9 (30 %) in normal subjects. Among 112 patients, 10 showed a canal paresis (CP) value of caloric testing less than 25 %, while 32 with a CP value between 25 and 40 %, 48 with a CP value between 40 and 70 %, and 22 with a CP value no less than 70 %. It is notable that with increasing CP value on caloric testing, VIN was more likely to be elicited. So VIN test is a simple, non-invasive and well-tolerated clinical test that indicates unilateral peripheral vestibular dysfunction. VIN test had greater sensitivity and specificity than HSN test in the diagnosis of unilateral peripheral vestibular disorders.