The background EEG activity is typically normal in the first year of life. Post-ictal slowing may be seen initially, diffuse slowing may appear over time.
By the second to fifth year of age, generalized spike-and-wave and multifocal discharges are seen.
Photic and pattern stimulation precipitate generalized spike-and-wave, with or without associated clinical events (atypical absence seizures and/or myoclonic seizures). Photosensitivity can be present in infancy and is seen at all ages. EEG abnormality is enhanced by sleep deprivation and by sleep.
The ictal EEG varies according to the type of seizure, refer to seizure type for more detail.
CAUTION The presence of diffuse electrodecremental patterns or paroxysmal fast activity are not seen consider Lennox Gastaut syndrome.