Background/Interictal EEG

The background EEG is abnormal in all states, with a suppression-burst pattern. High voltage bursts (150-300uV) of spikes or sharp and slow waves, lasting 1-5 seconds are seen with inter-burst intervals of 3-10 seconds.

The EEG may evolve to a hypsarrhythmia pattern in children who evolve to have West syndrome or to a pattern of multifocal spikes and sharp waves at 3-4 months of age.

Ictal

Erratic myoclonus usually does not have an ictal EEG pattern but may follow bursts on the EEG. Focal seizures are associated with focal ictal discharges, often superimposed on the suppression-burst background.