Background

The background EEG is normal.

CAUTION Focal slowing consistently over one area is not seen consider structural brain abnormality.

Interictal

A standard EEG can be normal in some patients. Multifocal high voltage spikes or sharp-waves are typically seen, these often are present in different focal areas on sequential EEGs. All focal brain regions may be affected but abnormality is often over the posterior (occipital) regions.

Example of multifocal spikes in self-limited epilepsy with autonomic seizures.

Example of occipital (left) spikes of high amplitude in self-limited epilepsy with autonomic seizures.

Activation

EEG abnormality is enhanced by sleep deprivation, in drowsiness and in sleep, when discharges often have a wider field and may be bilaterally synchronous. Eye closure (elimination of central vision and fixation off sensitivity) may activate posterior discharges in some patients.

Ictal

Ictal patterns are unilateral, often having posterior onset, with rhythmic slow (theta or delta) activity intermixed with small spikes and/or fast activity.