Atypical EEG findings in subacute sclerosing panencephalitis.

A total of 72 EEGs from 57 patients with SSPE were studied. The EEG studies in SSPE revealed periodic high amplitude complexes in all except one. Besides periodic complexes, we found several atypical EEG findings including frontal rhythmic delta activity in intervals between periodic complexes, electrodecremental periods following EEG complexes, diffuse sharp waves and sharp-and-slow-wave complexes over frontal regions, and focal abnormalities, such as sharp wave and sharp and slow wave foci, which have been rarely reported previously. We also described a new finding characterized by high amplitude generalized rhythmic sharp wave activity following periodic complexes in one patient.