Clinical significance of vibration-induced nystagmus and head-shaking nystagmus through follow-up examinations in patients with vestibular neuritis

To verify if vibration-induced nystagmus (VIN) in patients with vestibular neuritis changes over time and to compare the results of VIN test to those of caloric test and head-shaking nystagmus (HSN) test. Retrospective study of a series of cases. We compared VIN and HSN tests using caloric test results in 22 patients (male-to-female ratio, 11:11; age range, 15-67 yr) with acute vestibular neuritis seen at onset and in follow-up after 2 months. The eye movement recordings were made, and the maximum slow-phase eye velocities (SPVs) were calculated during vibration and after head shaking. If spontaneous nystagmus was present, it was subtracted from the SPVs of VIN and HSN. Positive value of the SPVs means slow-phase eye movement to the lesioned side. In acute stage, VIN of which SPV was directed toward the lesioned side was observed in 21 (95%); and HSN, in 22 (100%). In follow-up, VIN of which SPV was directed toward the lesioned side was observed in 19 (86%); and HSN, in 17 (77%). There was a significant decrease of the SPV of VIN and HSN over time. Significant correlations were observed in between canal paresis and SPV of VIN but not in between canal paresis/SPV of VIN and SPV of HSN. Although VIN test can predict the severity of vestibular asymmetry in acute and follow-up stages, HSN test could only probe vestibular asymmetry and could not predict the severity of the vestibular asymmetry. Our results suggest that VIN might represent the peripheral vestibular asymmetry; however, HSN might represent the stored vestibular asymmetry in velocity storage system, which is induced by peripheral asymmetry.