Age of seizure onset, functional reorganization, and neuropsychological outcome in temporal lobectomy

Abstract

Patients with early onset seizure disorder tend to have less cognitive decline following surgical resection than patients with late onset seizure disorder. Differential opportunity for presurgical cerebral functional reorganization has been proposed to account for this "age of onset" effect. However, the relationships between age of seizure onset, functional organization, and neuropsychological outcome remain incompletely understood. To shed additional light on these issues, we investigated 66 patients with anterior temporal lobectomies (37 left; 29 right), all of whom completed comprehensive neuropsychological assessment prior to and following surgical resection. The sample was divided into two groups: 34 patients with early onset (EO) epilepsy and 32 patients with late onset (LO) epilepsy. We found the typical age of onset effect: post-surgically, EO patients demonstrated relatively better outcome in multiple neuropsychological domains, especially verbal memory, compared to LO patients. Based on presurgical Wada testing, 23 patients were classified as having traditional cerebral functional organization (TFO) and 35 were classified as having nontraditional cerebral functional organization (NTFO). The NTFO group had an earlier age of seizure onset than the TFO group, and NTFO was more frequent in EO patients (70%) than LO patients (50%). NTFO patients demonstrated relatively better post-surgical outcome in several neuropsychological domains, compared to TFO patients. Our findings are consistent with the notion that functional reorganization may be an explanatory factor for the better neuropsychological outcome of EO epilepsy patients following anterior temporal lobectomy.

Figure 1

Neuropsychological change scores (post-surgery minus pre-surgery) by age of onset [early onset (EO) vs. late onset (LO)]. The bars on the x-axis are ordered from left to right to correspond with the top-to-bottom ordering of the key on the right.

Figure 2

Neuropsychological change scores (post-surgery minus pre-surgery) by functional organization [traditional functional organization (TFO) vs. nontraditional functional organization (NTFO)]. The bars on the x-axis are ordered from left to right to correspond with the top-to-bottom ordering of the key on the right.

Figure 3

Neuropsychological change scores (post-surgery minus pre-surgery) by onset classification and lobectomy hemisphere [early onset/left temporal lobectomy (EO/LTL) vs. early onset/right temporal lobectomy (EO/RTL) vs. late onset/left temporal lobectomy (LO/LTL) vs. late onset/right temporal lobectomy (LO/RTL)]. The bars on the x-axis are ordered from left to right to correspond with the top-to-bottom ordering of the key on the right.