The EEG background can be normal at onset, however diffuse slowing of the background occurs with time.
Multifocal discharges appear with time in all cases. Rarely hypsarrhythmia is reported.
EEG abnormality is enhanced by sleep deprivation, in drowsiness and in sleep.
The ictal EEG should show involvement of multiple independent cortical regions. A migrating pattern is confirmed (this may require prolonged EEG) when there is involvement of multiple independent cortical regions consecutively in the same seizure.