Ictal scalp EEG in temporal lobe epilepsy with unitemporal versus bitemporal interictal epileptiform discharges

We investigated the ictal scalp EEG in 228 seizures of 36 patients with unitemporal (n = 25) or bitemporal independent (n = 11) interictal epileptiform discharges (IED). All patients had proven temporal lobe epilepsy since they became seizure-free or only had auras after temporal lobectomy with a minimum follow-up of 1 year. Ictal patterns at seizure onset or later in the course of the seizure were lateralized significantly more often in patients with unitemporal IED (90%, at seizure onset and 96%, later) compared with those with bitemporal independent IED (75%, at seizure onset and 78%, later). Furthermore, scalp ictal EEGs, when lateralized at seizure onset or later in the course of the seizure, were significantly more likely to predict the correct side for surgery in patients with unitemporal (98%, at seizure onset and 100%, later) than bitemporal (64%, at seizure onset and 77%, later) IED. Bilateral independent seizure onsets, asynchrony of ictal activity over the two temporal lobes, and switch of ictal activity from one to the other hemisphere are ictal patterns that are strongly correlated with bitemporal excitability.