■ OBJECTIVES: It has been reported that vibration applied on the mastoid induces nystagmus in patients with vestibular disorders. The aims of the study were to characterize the vibration-induced nystagmus (VIN) in patients with unilateral Meniere’s disease (MD) and vestibular neuritis (VN), and to clarify the clinical significance of VIN by comparing VIN results with caloric results and comparing the results in between MD and VN.

■ METHODS:We recorded eye movements during unilateral 100 Hz vibration on the mastoid bone in 24 patients with MD and 22 patients with VN. Eye movements were analyzed assuming all the lesions to be left-sided and the maximum value of slow-phase eye velocity (SPV) obtained during vibration on each mastoid was used. Spontaneous nystagmus was subtracted from SPV of VIN, if it were present. A caloric unilateral weakness (UW) > 25% was considered pathologic.

■ RESULTS: In VN, all patients showed pathologic UW and VIN of which the direction of SPV was toward the lesioned side. In MD, pathologic UW was present in 9 (38%) and 8 of them showed SPV of VIN to the UW side. Fifteen (63%) out of 24 MD patients showed VIN of which the direction of SPV was toward the lesioned side. However, VIN of which the direction of SPV was toward the intact side was found in 8 patients. Among them, all 3 patients with mean SPV of VIN > 5°/s showed also UW to the intact side, although it was not pathologic. The amplitude of SPV showed a significant correlation with UW of caloric test in patients with either VN or MD. And there was no significant difference in the slope of the regression lines between them.

■ CONCLUSIONS: Our results suggest that VIN test may represent imbalance of canal responses to low frequency stimulation just like caloric test and show that VIN test can help in detecting vestibular imbalance with different stimulation mechanism from the caloric test. VIN test also showed limitation in localizing the lesioned side in patients with MD, like caloric test.