Sydenham's chorea: clinical, EEG, CT scan, and evoked potential studies.

An 8-year-old child developed acute mental confusion, and choreoathetosis without a preceding history of acute rheumatic fever. Serial EEGs showed focal suppression of sleep spindle activity over the right cerebral hemisphere along with high-amplitude polymorphic slow-wave complexes. CT scan studies on 4 occasions and MRI scan failed to show focal lesions corresponding to the clinical manifestations. Results of brainstem auditory evoked potential studies were normal. The short- and long-latency somatosensory evoked potential patterns were abnormal during the acute phase of illness as well as during the follow-up, when the patient was clinically intact. The persistent EEG and evoked potential abnormalities in the presence of clinical recovery from chorea raised questions as to the existence of a subclinical disease process.