The interictal EEG is usually normal. Ictal EEG may be obscured by artifact due to myoclonic jerks of the jaw and head. Ictal EEG findings of sharp-wave discharges have been reported, when these are noted they are bilateral but with a dominant hemisphere (temporal-parietal) maximum.
Interictal EEG findings reflect the underlying etiology e.g. structural brain abnormality. Ictal EEG shows an initial midline vertex discharge followed by diffuse attenuation or low voltage fast activity (which may have onset or emphasis in areas of structural brain abnormality, and then spread). Ictal EEG may be obscured by myogenic artifact.