We report the case of a 46-year-old man who presented with acute vertigo and positional upbeat nystagmus and was diagnosed as having cerebellar infarction due to dissection of the posterior inferior cerebellar artery (PICA). On the day of onset, the patient suffered a 10-minute acute vertigo episode, followed by disequilibrium. On the same day, he visited the emergency department; however, there were no abnormal neurological and radiological findings, and he could walk back home. The following day, at the visit to an otolaryngologist, he was found to show positional upbeat nystagmus and mild incoordination of the right upper extremity. A head MRI was performed, which showed cerebellar infarction; furthermore, MRI revealed dissection of the PICA. Vestibular function tests showed no abnormalities. However, the saccade test showed hypometria, and visual suppression was poor. He was asymptomatic by the ninth day after symptom onset and remained on oral antiplatelet medication for the next eight months. Our case indicates that importance of close spontaneous nystagmus detection in the differential diagnosis of acute vertigo.
