Background

The background may be normal at onset, progressive slowing of the background appears with time.

Interictal

Generalized spike- and polyspike-waves are seen. Focal epileptiform abnormality may be seen in posterior regions in Lafora disease.

Activation

Depending on the underlying cause, photic stimulation may facilitate spike-wave discharges on EEG, this is seen in Unverricht-Lundborg disease, Lafora disease and in the neuronal ceroid lipofuscinoses. There can be activation at low flash frequencies in Lafora disease and in specific neuronal ceroid lipofuscinoses e.g. CLN2. In contrast to genetic generalized epilepsies, generalized epileptiform abnormality may not be activated in sleep in Lafora disease (but focal abnormality in the posterior regions may be).

Ictal

A single generalized polyspike-wave may correlate with the jerk of a myoclonic seizure, however the erratic myoclonus of Lafora disease may occur without EEG correlate.