Frontal lobe dysfunction as a predictor of depression and anxiety following temporal lobe epilepsy surgery.

OBJECTIVE: Predictors of psychiatric outcome following TLE surgery have proved elusive and represent a current challenge in the practice of TLE surgery. This prospective study investigated whether frontal lobe dysfunction is predictive of poorer psychiatric outcomes.

METHODS: Forty-nine unilateral TLE surgical patients were assessed using the Beck Depression Inventory-Fast Screen (BDI-FS) and Beck Anxiety Inventory (BAI) preoperatively and 6 and 12 months postoperatively. Measures of intellectual function, semantic knowledge, memory and executive function were completed preoperatively, at 6 and 12 months following surgery.

RESULTS: Preoperatively, 33 (67%) patients had minimal depressive symptoms, 8 (16%) were mildly depressed, 2 (4%) were moderately depressed, and 6 (12%) reported severe depressive morbidity. Twenty-three (47%) patients reported minimal anxiety, 18 (37%) were mildly anxious, 6 (12%) were moderately anxious and 2 (4%) patients reported severe anxiety symptoms. A mixed-model repeated-measures analysis was performed on the BDI-FS and BAI scores, adjusting for pertinent covariates identified in univariable analyses. At a year following TLE surgery, anxiety symptoms significantly improved but depressive morbidity did not. Indicators of frontal lobe dysfunction moderated the magnitude and direction of mood change. Specifically, pre-surgical cognitive measures of frontal lobe dysfunction predicted increased depression and anxiety symptoms following surgery. There was no relationship between preoperative BDI-FS or BAI scores and seizure outcome at 12 months or change in affective morbidity and seizure outcome.

SIGNIFICANCE: This is the first longitudinal study to provide evidence that specific pre-surgical cognitive and behavioural indices of frontal dysfunction are predictive of poorer psychiatric outcome following TLE surgery. In addition, our findings highlight the potential utility of a dysexecutive behavioural rating scale (DEX) as an assessment tool in epilepsy. Examination of executive functioning in pre-surgical evaluations may lead to an increase in the power of prognostic models used to predict the psychiatric outcome of TLE surgery.