Background/Interictal/Activation

Please refer to specific syndromes and etiologies in which this seizure type occurs for specific information. As a general rule, EEG abnormality may be enhanced by sleep deprivation, in drowsiness and in sleep.

There are large areas of mesial and inferior frontal cortex that are not sampled by scalp EEG. The interictal EEG is frequently normal if the etiology of the epilepsy is a structural brain abnormality in these areas. Even with repeated EEGs, epileptiform discharges may only be seen in up to 70% of such patients. In these patients, discharges are typically midline or bi-frontal.

Ictal

Ictal EEG in frontal lobe seizures may be difficult to interpret. Seizures often involve hyperkinetic activity, which causes the EEG to be obscured by muscle artifact. Ictal EEG can demonstrate a localized ictal rhythm in lateral frontal lobe seizures with localized repetitive discharges. Ictal EEG in mesial frontal lobe seizures can often appear as a generalized EEG change, if an EEG change is present. These bilateral discharges often have an amplitude asymmetry, representing secondary bilateral synchrony rather than true generalized seizure onset, and may be preceded by generalized suppression of the EEG. Ictal EEG may also be characterized by diffuse or localized low voltage fast rhythms.

CAUTION False localization may occur, especially to the ipsilateral temporal lobe. Interpretation of seizure features in conjunction with ictal EEG is important in this situation.