Effects of neck muscle vibration on subjective visual vertical: comparative analysis with effects on nystagmus

In patients with unilateral vestibular dysfunction, vibratory stimulation to the neck muscles not only induces shift of the subjective visual vertical (SVV), but also enhances the generation of nystagmus. In the present study, the effects of neck vibration on the SVV were compared with those on nystagmus in patients with unilateral vestibular schwannoma (14 patients; 6 males and 8 females, mean age 54.2 years). The results indicated that the presence of nystagmus and magnitude of the SVV were generally correlated, neck vibration significantly increased the abnormal shift of the SVV and the presence of nystagmus, and the effects of vibration to the ipsilateral dorsal neck were significantly larger than those to the contralateral dorsal neck on the SVV, whereas no significant difference was observed in slow phase velocity of nystagmus. The present study suggests that both SVV and nystagmus induced by vibration have many similar clinical features and may be important in assessing the unilateral vestibular dysfunction.