Background

The background is normal. Occipital intermittent rhythmic delta activity (OIRDA) may be seen in around 20% of cases.

CAUTION Focal slowing seen consistently in one area consider structural brain abnormality.

CAUTION Generalized slowing is not seen.

Interictal

2.5-4Hz generalized spike-wave, or fragments of generalized spike-wave are seen in the interictal EEG. These are brief (usually <2 second) and most commonly seen in sleep.

CAUTION Although focal spikes (as fragments of generalized spike-wave) can occur, if they consistently arise in one area consider structural brain abnormality.

Activation

EEG abnormality and absence seizures are provoked by hyperventilation. If hyperventilation is poorly performed, generalized spike-wave may not be seen.

Intermittent photic stimulation provokes generalized spike-wave in 15-20% of individuals but does not provoke seizures.

EEG abnormality is enhanced by sleep deprivation, in drowsiness and in sleep. Generalized spike-wave often becomes fragmented with sleep deprivation or in sleep. Fragmented generalized spike-wave can appear focal or multi-focal but usually is not consistently seen in one area. The morphology of the focal spike-wave typically appears similar to the generalized spike-wave.

CAUTION Where hyperventilation is performed well for three minutes and no generalized spike-wave is seen in an untreated patient, childhood absence epilepsy is excluded.

Ictal

Regular 3Hz (range 2.5-4Hz) generalized spike-wave occurs associated with absence seizures. Polyspike-wave can occur in the ictal EEG.

CAUTION Slow spike-wave (<2.5Hz) is exclusionary.

Example of 3Hz generalized spike-wave seen on the ictal EEG