Opsoclonus persisting during sleep in West Nile encephalitis.

BACKGROUND Recent outbreaks of West Nile virus infection have alerted the public to disabling paralysis as an outcome. Ocular motor involvement with West Nile virus is rare. OBJECTIVE To describe a patient with West Nile virus encephalitis that resulted in opsoclonus-myoclonus syndrome with persistent ocular oscillation on electroencephalography during stage 2 sleep. PATIENT A 53-year-old man who presented with viral prodrome followed by intense vertigo and encephalopathy. In addition to multifocal myoclonic jerks in the extremities, his eye movements were disrupted by bursts of high-frequency, conjugate ocular oscillations that occurred in random directions. RESULTS Electroencephalography showed eye movement artifacts during the awake state and stage 2 sleep. Opsoclonus-myoclonus syndrome remained disabling 3 months after onset but markedly improved 8 months after onset. CONCLUSIONS West Nile virus is another cause of opsoclonus-myoclonus syndrome that can occur in conjunction with encephalitis. The presence of an eye movement artifact on results of electroencephalography during stage 2 sleep should raise suspicion for opsoclonus.