Clinical Implication and Proposed Mechanism of Direction Changing Vibration Induced Nystagmus in Unilateral Vestibular Hypofunction

Abstract

Background and Objectives We evaluated the clinical characteristics and vestibular function of patients with direction changing vibration induced nystagmus (DC VIN) and unilateral vestibular hypofunction and suggest clinical implication and a proposed mechanism of DC VIN. Subjects and Method The records of 315 patients who underwent the VIN test were reviewed retrospectively. Among these, 18 patients (5.7%) showed DC VIN, and out of whom, 15 patients (4.8%) were diagnosed as unilateral vestibular hypofunction by caloric, rotation chair (RCT), and video head impulse test (vHIT). We analyzed the relationship between DC VIN and the dizziness characteristics, duration of disease, and the outcome of the vestibular function test. Results The mean age of 15 patients was 67.4±10.7 years and the mean duration of dizziness was 13.6±29.7 months. The caloric test revealed 25% of the patients to have significant canal paresis [Caloric vestibular neuritis (VN)], while 75% showed normal caloric response. However, unilateral vestibular hypofunction was observed by abnormal results in RCT or vHIT (Non-caloric VN). Seven patients showed ipsilateral DC VIN (nystagmus to vibrated side) and eight patients contralateral DC VIN (nystagmus to opposite side of vibration). Patients with ipsilateral DC VIN were shown to have a significant longer duration of dizziness than those with contralateral DC VIN. Conclusion Although rare, DC VIN can also be found in patients with unilateral vestibular hypofunction. Patients with DC VIN had a mild vestibular asymmetry with Non-caloric VN or Caloric VN in the process of compensation. The mechanism of ipsilateral DC VIN seems to be due to the small amount of vestibular asymmetry, which is smaller than the interaural attenuation of vibration.