[Rhythmic involuntary movement of the neck in a patient with brainstem encephalitis].

A 36-year-old Japanese woman was admitted to our hospital, because of facial palsy, ophthalmoplegia, cerebellar ataxia, and rhythmic myoclonus of the neck. About a few weeks before admission, she developed symptoms of common cold and general fatigue. Her laboratory data were unremarkable, and her CSF was normal. Serum levels of antibodies to gangliosides were within normal limits. Her MRIs of the brain and neck were normal. Both somatosensory evoked cortical potential study and auditory evoked brainstem response study were normal. She was diagnosed as postinfectious brainstem encephalitis, and the administration of corticosteroid was started. After the treatment, her symptoms improved. To our knowledge, it is rare to see myoclonus to the neck without palatal tremor in patients with brainstem encephalitis.