Intracarotid amobarbital procedure memory performance and age at first risk for seizures distinguish between lateral neocortical and mesial temporal lobe epilepsy

Purpose: To determine whether intracarotid amobarbital procedure (IAP) memory-performance asymmetries and early risk factors for epilepsy distinguish between lateral neocortical temporal lobe epilepsy (LNTLE) and mesiobasal temporal lobe epilepsy (MBTLE). Methods: We studied 10 patients with LNTLE and 22 with MBTLE. All LNTLE patients showed (a) presence of temporal neocortical lesion or lateral seizure onset by intracranial recording, and (b) absence of mesial temporal sclerosis (MTS) by histopathologic analysis. All patients with MBTLE showed (a) video-scalp EEG seizures consistent with mesial TLE, and (b) presence of unilateral MTS by histopathologic analysis. All patients had good surgical outcomes (Engel I or II). Unilateral IAP memory performance was defined as percentage of memory items presented during hemispheric anesthesia that was recognized after recovery. IAP asymmetry scores were the differences in memory performance after right and left injections. Results: Mean memory-asymmetry scores were significantly lower in the LNTLE than in the MBTLE group. An IAP memory asymmetry of <25% correctly classified seven of 10 patients with LNTLE, and an asymmetry of greater than or equal to 25% correctly classified IS of 22 patients with MBTLE. Age at first risk for epilepsy was significantly younger in those with MBTLE than in those with nonlesional LNTLE. Results suggest that both IAP memory performance and age at first risk can help distinguish between MBTLE and LNTLE.