Background

The background EEG is normal.

CAUTION Generalized slowing is not seen.

Interictal

Generalized spike-and-wave discharges and polyspike-and-wave discharges may occur.

CAUTION Focal discharges consistently over one region consider structural brain abnormality.

Activation

EEG abnormality (and myoclonic absence seizures) may be provoked by hyperventilation. Intermittent photic stimulation triggers generalized spike-and-wave in a minority of patients.

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.

Ictal

Regular 3-Hz generalized spike-and-wave accompanies myoclonic absences. EMG recordings from the upper arm show a constant relationship between the bilateral myoclonic jerks and spike-and-waves.

CAUTION Slow spike-and-wave (<2.5Hz) consider atypical absence seizures in Lennox Gastaut syndrome.