The background EEG may be normal, or may show focal or widespread slowing.
Focal interictal epileptiform abnormality may be seen. Multi-focal independent spikes or generalized spike-wave (usually <3Hz) may also occur.
EEG abnormality is enhanced by sleep deprivation, in drowsiness and in sleep.
The presence of focal, rhythmic epileptiform discharges may be seen, with focal seizure types. If generalized seizures are present, the ictal EEG associated with these seizure types may be seen.