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CHILDHOOD ABSENCE EPILEPSY

Background

The background is normal. Occipital intermittent rhythmic delta activity (OIRDA) may be seen in a third of children with childhood absence epilepsy, at a frequency of 2.5-4 Hz, and may have a notched appearance.

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

CAUTION Generalized slowing is not seen.

Interictal

Generalized spike-and-wave, or fragments of generalized spike-and-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-and-wave) can occur, if they consistently arise in one area right arrow consider structural brain abnormality.

Activation

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

Intermittent photic stimulation triggers generalized spike-and-wave in a small proportion of individuals.

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.

CAUTION Where hyperventilation is performed well for three minutes and no generalized spike-and-wave is seen, childhood absence epilepsy is unlikely.

Ictal

Regular 3 Hz generalized spike-and-wave occurs associated with absence seizures. Polyspike-and-wave can occur in the ictal EEG.

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

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

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