[Steroid responsive chronic brainstem encephalitis featuring mental symptoms, abnormal eye movement and cerebellar ataxia].

A 53-year-old man presented with progressive ataxia two and a half years prior to admission. Initially he was treated in a local hospital for 4 months with a diagnosis of spinocerebellar degeneration. Subsequently he developed psychomotor excitement with hallucination and was admitted to a mental hospital for 7 months with a diagnosis of Wernicke's encephalopathy. After a year of partial remission, he presented with increasing difficulty in thinking and walking. On admission he developed mental agitation and excitement, ocular flutter and opsoclonus, and prominent cerebellar ataxia. A lymphocytic pleocytosis in the CSF and a high-intensity lesion in the superior cerebellar peduncle of the upper brainstem revealed on a T2-weighted MRI led to a diagnosis of brainstem encephalitis. Treatment with steroid (two series of 3 days of 1,000mg methylprednisolone DIV, followed by 60mg oral prednisolone) brought about a dramatic improvement in mental and ocular symptoms corresponding with the CSF findings. He was left with mild cerebellar ataxia and returned to work on a small dose of steroids. Differential diagnoses including Bickerstaff's encephalitis and pathomechanism were discussed.