The background is typically abnormal with slow (theta-delta) activity seen, predominantly in the central or parieto-occipital regions.
The interictal EEG shows multifocal continuous spikes, sharp waves, or continuous slow waves.
Spikes may be superimposed on parieto-occipital slow activities with eye closure.
EEG abnormality persists in early sleep cycles, but in later sleep cycles in the night and in slow wave sleep, the abnormality improves and myoclonic jerks cease.
Myoclonic jerks may not correlate with EEG findings or may be accompanied by diffuse or multifocal slow spike-and-wave discharges or by anterior-predominant rhythmic theta or delta activities.