Cognitive outcome two years after frontal lobe resection for epilepsy – A prospective longitudinal study

PURPOSE To investigate cognitive outcomes after frontal lobe resection (FLR) for epilepsy in a consecutive single centre series. METHODS Neuropsychological examinations were performed prior to and two years (mean test interval 2.5 years) after surgery in 30 consecutive patients who underwent FLR. Cognitive outcome was evaluated with particular consideration to the site of surgery (lateral, premotor/SMA [supplementary motor area], mesial/orbital). Cognitive domains assessed were speed, language, memory, attention, executive functions and intelligence. 25 healthy controls were assessed at corresponding time points (mean test interval 3.0 years). Analyses were made both at group and individual levels. RESULTS At baseline the patients performed below controls in variables depending on speed, executive functions, global and verbal intelligence. Two years after surgery, the analyses at the subgroup level indicated that the lateral resection group had less improvement than the controls in global intelligence, FSIQ (p=.037). However, at the individual level, the majority of the change scores (74-100%) were classified as within the normal range for all but one variable. The exception was the variable "Comprehension" (measuring verbal reasoning ability) with reliable declines in 44% (8/18) of the patients. This pattern of decline was observed in the lateral (4/7 patients) and premotor/SMA (4/7 patients) resection groups. Seizure outcome and side of surgery did not influence these results. CONCLUSION The main finding was cognitive stability at group level two years after FLR. A reliable decline in verbal reasoning ability was rather common at an individual level, but only in the lateral and premotor/SMA resection groups. The lateral resection group also had less improvement than the controls in global intelligence.