Abstract
The patient is a 14-year-old boy. The onset of the episode was marked by fever, headache and gait disturbance. The initial examination revealed spontaneous downbeat nystagmus, bilateral gaze nystagmus with rebound nystagmus, truncal ataxia, and an increased cerebular count and protein volume in the cerebrospinal fluid. About one month later, there was no clear downbeat nystagmus, but so-called nystagmus alternans was observed. In this case, the downbeat nystagmus and rebound nystagmus observed early during the course of the disease, as well as cerebellar symptoms, suggested that the main lesion was located in the cerebellum. As inflammation was suspected from fever observed at the onset and the abnormal CSF findings, he was diagnosed as having had acute cerebellitis. The nystagmus alternans in this case disappeared seven months after the onset.
