Focal interictal spikes or polyspikes may be seen over the abnormal hemisphere.
Multi-focal independent spikes or generalized spike-and-wave (usually < 3 Hz) can be seen in those with generalized seizure types.
Hypsarrhythmia can be seen in those with epileptic spasms.
EEG abnormality is enhanced by sleep deprivation and in sleep. Obtaining a sleep EEG is important in infants at risk of epileptic spasms, as the awake EEG may not show typical abnormality associated with epileptic spasms, this abnormality may only be present in sleep.
Focal rhythmic epileptiform discharges are seen with focal seizures arising in the hemimegalencephalic hemisphere.