Preclinical EEG abnormalities in subacute sclerosing panencephalitis.

Persistent electroencephalographic (EEG) abnormalities were observed for 4 years before the clinical onset of subacute sclerosing panencephalitis (SSPE) in a girl initially chosen as a "normal" control subject. Neurologic or mental changes were not observed during this period. Initially, there were focal paroxysmal discharges with shifting characteristics. Nonrepetitive generalized slow-wave complexes during wakefulness appeared later and persisted 3 weeks after onset of clinical manifestations. SSPE repetitive complexes were observed 1 month later. Multifocal paroxysmal EEG discharges during the presymptomatic stage of SSPE probably arise from restricted cortical areas containing persistently infected neurons and indicate that despite relative tolerance, the brain is not completely unresponsive to the presence of the virus.