Background

The background is normal at onset. Biparietal monomorphic theta rhythms may be seen. With increased seizure frequency, generalized slowing may be seen.

Example of bi-parietal theta.

CAUTION Focal slowing consistently over one area consider structural brain abnormality.

Interictal

2-6Hz generalized spike- and polyspike-wave is seen.

CAUTION Generalized paroxysmal fast (≥10Hz) activity in sleep consider Lennox-Gastaut syndrome.

Activation

Hyperventilation may elicit generalized spike-wave and absence seizures (if present clinically), photosensitivity is rare.

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

Ictal

The myoclonic component of a myoclonic-atonic seizure is associated with a generalized spike or polyspike. The atonic component is associated with the aftergoing high voltage slow wave. During non convulsive status, the EEG shows long runs of high amplitude 2-3Hz irregular generalized spike-wave with background slowing.