Background

The EEG background is abnormal in all cases, with generalized or focal slowing.

CAUTION Prominent bi-parietal rhythmic theta consider epilepsy with myoclonic atonic seizures.

Interictal

Generalized slow (<2.5Hz) spike-wave and generalized paroxysmal fast activity (≥10Hz) in slow wave sleep are mandatory for the diagnosis of this syndrome. Slow spike-wave is no longer seen by adulthood and therefore may need to be confirmed on historic EEG. There may be focal or multifocal spike- or sharp-waves, with an anterior predominance. Periods of suppression of the EEG may occur.

CAUTION Fast spike-wave (3Hz or higher) consider other epilepsy syndromes.

CAUTION Spike-wave activation in sleep consider developmental and/or epileptic encephalopathy with spike-wave activation in sleep.

Activation

Hyperventilation (if adequate co-operation) may facilitate spike-wave and atypical absences.

CAUTION If activation with intermittent photic stimulation consider epilepsy with myoclonic atonic seizures.

CAUTION If photoparoxysmal response at low flash frequency consider CLN2-disease.

Ictal

For ictal EEG patterns, refer to individual seizure types.