上眼瞼向き垂直性頭位眼振がみられた突発性難聴症例

抄録

Upbeat nystagmus is a sign of a central nervous system disorder. Herein, we report a patient with positional upbeat nystagmus in the straight supine position with no evident abnormal central nervous system findings.

A 58-year-old woman visited our clinic complaining of feeling dizzy and a sense of fullness in the right ear since the day before. Initially, the supine head roll test revealed upbeat nystagmus for 50 s with latency of 3 s in the straight supine position. In the prone seated position, oblique nystagmus toward the down and right side was observed for 55 s with a latency of 17 s. No nystagmus was observed in the other head positions in either the supine head roll test or the Dix–Hallpike test. The pure tone audiogram showed low frequency sensorineural hearing loss in the right ear. Neurological examination, brain magnetic resonance imaging and magnetic resonance angiography revealed no abnormal findings. The patient was treated with oral isosorbide and betahistine. Within 5 days of the start of this treatment, the nystagmus, vertigo, as well as the low-frequency sensorineural hearing loss resolved completely.

We speculated that the positional upbeat nystagmus and low frequency sensorineural hearing loss in this patient were not caused by central nervous system disorder, but by some peripheral lesions, and that the pathophysiological basis of the nystagmus was canalolithiasis of the bilateral posterior semicircular canals.