The background is EEG normal.
CAUTION Generalized slowing is not seen.
CAUTION Focal slowing consistently seen in one area consider structural brain abnormality.
The interictal EEG may have generalized spike-and-wave and polyspike-and-wave, usually at 3.5-6Hz. In one third of cases, fragmented generalized spike-and-wave can appear focal or multi-focal, but usually is not consistently seen in one area.
CAUTION Focal spikes consistently seen in one area consider structural brain abnormality.
CAUTION Slow spike and wave (<2.5 Hz) is not seen consider other epilepsy syndromes.
A photoparoxysmal response to intermittent photic stimulation is seen in one third of cases, however seizures induced by visual stimuli in daily life are seen in <10%.
Generalized spike-and-wave or polyspike-and-wave and clinical absences may be provoked by hyperventilation.
CAUTION Where hyperventilation is performed well for three minutes and no generalized spike-and-wave is seen, absence seizures are unlikely.
EEG abnormality is enhanced by sleep deprivation and by sleep. Generalized spike-and-wave often becomes fragmented with sleep deprivation or in sleep. Fragmented generalized spike-and-wave can appear focal or multi-focal but usually is not consistently seen in one area. The morphology of the focal spike-and-wave typically appears similar to the generalized spike-and-wave.
A single generalized polyspike-and-wave correlates with the myoclonic seizure.
With generalized tonic-clonic seizures, the ictal EEG is often obscured by artifact. Generalized fast rhythmic spikes are seen in the tonic stage. Bursts of spikes and after-coming slow waves are synchronous with clonic jerks. A postictal period of irregular slow activity follows.
Regular fast (3.5-6Hz) generalized spike-and-wave or polyspike-and-wave accompanies absence seizures.