A case of acquired nystagmus alternans associated with acute cerebellitis.

A case of acquired nystagmus alternans (alternating nystagmus) is reported. The patient was a 14-year-old boy who presented with fever and headache, followed by dysbasia, truncal ataxia, and positional vertigo. Neuro-otological examinations revealed spontaneous downbeat nystagmus, bilateral gaze nystagmus and rebound nystagmus. Both cell count and protein volume were elevated in the cerebrospinal fluid, and a diagnosis of cerebellitis was made. About one month later, nystagmus alternans was observed, but it disappeared after 7 months. The presence of spontaneous downbeat nystagmus, rebound nystagmus, as well as cerebellar signs indicated that a cerebellar lesion was mainly responsible for the nystagmus alternans in this patient.