Falsely localizing ictal onsets with depth EEG telemetry during anticonvulsant withdrawal.

A patient with partial complex seizures evaluated for surgery with chronic depth electrode recordings demonstrated falsely localizing ictal onsets during anticonvulsant drug withdrawal. When phenytoin was being reduced, more seizures appeared to originate from the left temporal lobe than from the right. Right anterior temporal lobectomy, performed on the basis of other findings, revealed a small unsuspected tumor in the resected specimen, and the patient has remained seizure free for 3 years. The seizures that originated from the left temporal lobe were different from the patient's habitual attacks and appeared to be the result of anticonvulsant withdrawal and, perhaps, electrode irritation. Four other patients who received anterior temporal lobectomies at UCLA between 1977 and 1980 had at least one stereotaxic EEG (SEEG)-recorded contralateral seizure onset, and all have benefited from surgery. Although multifocal SEEG-recorded ictal onsets should be considered a poor prognostic sign, distant sites that give rise to atypical seizures during drug withdrawal may not generate spontaneous seizures postoperatively. Consequently, this finding should not be used as a sole criterion against the recommendation of surgical therapy.