Abstracts

Rationale: There are just a few studies about improvements in cognitive functioning after successful epilepsy surgery. In contrast, the risks of deteriorations in cognitive functions following surgery are well described, mainly focusing on memory losses after temporal lobe surgery. Impairments after successful surgery are caused by postoperative lesions. Based on the multi-causal model of cognitive functions in epilepsy, gains can be explained by unspecific factors like the cessation of seizures or interictal discharges. Taking this model, we hypothesize that gains mainly take place in functions located remote to the lesion or in wide-spread networks. The following study aims to test this prediction by using four subtests of the Wechsler Intelligence Scale in a sample of 45 surgically treated patients with temporal lobe epilepsy. Methods: This retrospective study included all temporal lobe patients without missing data in a four-subtest short form of the Wechsler Adult Intelligence Scale (subtests: Vocabulary, Similarities, Arithmetic, Block Design). Only adult patients with a significant reduction in seizure frequency (Engel IA to Engel IIB) were included, excluded were patients with lateral lesionectomies for tumors. Patients were assessed preoperatively and about 24 months postoperatively. The total sample comprised 45 patients (23 left TLE, 22 right TLE). There were no differences in the demographic and medical background data between the right and left group. We performed a repeated measures MANOVA to test if there is a significant interaction between time (pre/post) and group (left/right) on the dependent variables (subtest scores). Results: The repeated measures MANOVA showed a significant interaction between time and group (F=3.174; p=.023). On subtest level, the interaction was significant in the Block Design subtest (F=4.255; p=0.045) and in the Vocabulary subtest (F=5.591, p=.023). A significant gain of 4.26 raw score points in the Block Design subtest was only found in patients operated on the left side but not in patients operated on the right side. A significant gain in the Vocabulary subtests (2.50 raw score points) was found only in patients operated on the right side. Conclusions: The results show that postoperative gains in global intellectual functioning depend on the side of surgery. There is an impressive gain in the Block Design subtest assessing broad non-verbal functioning only in patients operated on the left side and a significant gain in the Vocabulary subtest assessing broad verbal functioning only in patients operated on the right side. This supports a model of release of remote, previously suppressed functions after successful surgery. Therefore, cognitive impairment in drug-resistant focal epilepsy may partly be reversible due to normalization of brain function after cessation of seizures. The results of this study improve the understanding of the dynamics of global cognitive impairments in focal epilepsies and are important for informed consent. Funding: No funding was received in support of this abstract.