Executive performance on the Wisconsin Card Sorting Test in mesial temporal lobe epilepsy

Executive dysfunction assessed by the Wisconsin Card Sorting Test has been observed in patients with mesial temporal lobe epilepsy (TLE); however, the mechanism of executive impairment is unclear. We therefore investigated the potential contribution of the hippocampus toward executive dysfunction in 85 mesial TLE patients, and in a control group of 34 patients with neocortical TLE. Standardized regression-based methodology was used for correcting test-retest bias. We found that 56% of mesial TLE patients had impaired sorting performance, with 30% showing severe impairment. A lower full-scale intelligence quotient, older age, longer duration, and preoperative use of topiramate were significantly correlated with poorer preoperative sorting abilities. However, neither these variables nor postoperative discontinuation/reduction of topiramate were related to postoperative changes in sorting abilities. Only preoperative sorting abilities were negatively correlated with postoperative changes in executive performance. That is, patients with better preoperative executive ability showed greater postoperative deterioration in executive function, whereas those with poorer preoperative sorting ability had greater improvement in executive function after mesial temporal resection. There were no differences in card sorting ability between the mesial and neocortical TLE groups. In conclusion, our results suggest that impairment of card sorting performance in the mesial TLE group cannot be explained only by hippocampal dysfunction, but that other processes (possibly epileptic discharges propagated to the extratemporal area) must play a predominant role.