The epileptogenic zone in pharmaco-resistant temporal lobe epilepsy with amygdala enlargement.

Abstract

Temporal lobe epilepsy with amygdala enlargement (TLE-AE) has been considered a subtype of TLE. We evaluated the epileptogenic zone in patients with TLE-AE, who underwent intracranial video-EEG (ivEEG) and/or intraoperative electrocorticography (ioECoG) as well as epilepsy surgery. Eleven patients with TLE-AE were enrolled and investigated based on seizure profile, volumetric MRI, the Wechsler Memory Scale-Revised (WMS-R), the location of seizure onset zone (SOZ) and irritative zone (IZ) based on ivEEG (n=8), the location of interictal epileptiform discharges (IEDs) based on ioECoG (11), surgical procedure, and seizure outcome. The mean age at seizure onset was 34.9 years (range: 23-57). The mean duration of seizures was 5.0 years (range: 1-10). The number of AEDs was 2.3 (range: 1-5). The mean seizure frequency was nine per month (range: 1-30/month). All patients presented with focal impaired awareness seizures with (n=9) and without (2) secondary generalized convulsions. Volumetric MRI analysis showed unilateral enlarged amygdala with statistical significance (p<0.01). None of the patients hippocampi had any abnormality based on MRI. Pre-operative mean verbal, visual, and delayed recall scores based on the WMS-R were over 100. The SOZ and IZ were identified in both the amygdala and hippocampus in seven patients and in only the amygdala in one patient based on ivEEG. IEDs were identified in the hippocampus in six patients and in both the amygdala and hippocampus in four patients based on ioECoG. All 11 patients underwent anterior temporal lobectomy, including amygdala resection, with multiple hippocampal transections (dominant hemisphere: seven patients) and resection (non-dominant hemisphere: three patients). Nine (81.8%) of 11 patients achieved seizure freedom with a mean follow-up of 26 months (range: 12-47). Post-operative WMS-R results did not show any significant deterioration, with a mean follow-up of 15 months (range: 12-24). The resected amygdala showed no histopathological abnormality. The epileptogenic zone of TLE-AE involves both the amygdala and hippocampus. ivEEG may be needed to explore the SOZ in normal hippocampus in addition to enlarged amygdala. Amygdala resection and multiple hippocampal transections may control the epileptogenic limbic system and save memory function in patients with TLE-AE.