Clinical significance of vibration-induced nystagmus.

The aims of the study were to characterize the vibration-induced nystagmus (VIN) in patients with unilateral vestibular neuritis (VN) and Ménière's disease (MD), and to clarify the clinical significance of VIN by comparing it with caloric results in patients with VN and MD. We recorded eye movements from 22 VN patients and 24 MD patients using unilateral 100-Hz vibration on the mastoid bone. Eye movements were analyzed and the maximum value of slow-phase eye velocity was obtained during vibration on each mastoid. The average value of slow-phase velocities was calculated. Spontaneous nystagmus was subtracted from the slow-phase velocity, whenever it was present. A canal paresis (CP) greater than 25% was considered pathologic. All but one VN patient showed pathologic CP with the direction of the slow-phase eye movement of VIN toward the lesioned side. Fifteen (63%) out of 24 MD patients showed VIN with the slow-phase eye movement directed to the lesioned side. Pathologic CP was present in 9 (38%) out of 24 MD patients and 8 of them showed slow-phase eye movements of VIN directed to the lesioned side. There were also 8 other MD patients who showed slow-phase eye movement of VIN directed to the intact side. Among them, 3 patients with the slow-phase eye movement more than 5 degrees /s showed CP on the intact side. The amplitude of slow-phase eye velocity showed a significant correlation with CP in patients with either VN or MD. There was no significant difference in the slope of the regression lines between the VN and MD groups. Our results suggest that VIN may probe imbalance of canal responses to low-frequency stimulation similar to the caloric test. It also shows that VIN can help in detecting vestibular imbalance using a stimulation mechanism different from the caloric test. The VIN test can be helpful in determining the lesioned side in patients with VN; however, it has some limitations in localizing the lesioned side in patients with MD.