Background

The background EEG is typically normal.

CAUTION Focal slowing consistently over one area consider structural brain abnormality.

Interictal

There are no epileptiform abnormalities seen in the awake EEG in most patients. During sleep, epileptiform abnormalities are seen over the frontal areas in approximately 50% of patients.

Activation

Epileptiform abnormality is enhanced by sleep deprivation and in sleep.

Ictal

Ictal EEG may not show definitive ictal patterns, be obscured by movement artifact, or show evolving sharp-or spike-wave discharges, rhythmic slow activity, or diffuse background flattening. Postictal focal slowing may be seen. Prolonged video–EEG recording is the best diagnostic test to identify the characteristic seizures from sleep to confirm the diagnosis, especially in cases without a clear ictal EEG patterns. Intracranial EEG recordings (e.g., stereo-EEG) have demonstrated that ictal discharges may start in frontal or extrafrontal areas (including in insulo-opercular, temporal and parietal cortices).