Abstracts

Depression is a common and important co-morbidity in patients with medically refractory temporal lobe epilepsy (TLE). In particular, at least 30% of patients who undergo surgery for medically refractory TLE develop clinical depression in the first three months following the surgery. The reasons underlying the association between depression and TLE is uncertain, with both neurobiological and psychosocial explanations postulated. FDG-PET shows hypometabolism in the frontal lobes of depressed non-epileptic patients, and many patients with TLE have hypometabolism involving frontal regions. We studied the patterns of FDG-PET hypometabolism in patients undergoing surgery for medically refractory TLE to determine whether patients who had clinical depression pre-operatively and/or post-operatively demonstrated differences from non-depressed patients. A cohort of 23 patients who underwent an anterior temporal lobectomy for medically refractory TLE, had an FDG-PET scan performed as part of their pre-operative evaluation, and had a formal pre- and post-operative psychiatric assessment, were studied. Statistical parametric mapping (SPM-99) was used to compare the patterns of hypoperfusion on FDG-PET between patients who were depressed pre-operatively (n=9) and those who were not (n=14), as well as between those who developed post-operative depression (n=13) compared to those who did not (n=11). The level for determining a significant region of hypometabolism was set at p[lt]0.001 for a cluster of at least 20 contiguous voxels. Pre-operatively depressed patients showed a focal region of hypometabolism in the region of the ipsilateral orbitofrontal cortex compared with those who were not ([italic]t[/italic]= 4.64 P[lt]0.001). Patients who developed depression post-operatively also showed a similar region of significant hypometabolism in the ipsilateral orbitofrontal frontal region ([italic]t[/italic]= 5.10, P[lt]0.001). These results demonstrate a focal region of relative hypometabolism in the ipsilateral frontal lobe on FDG-PET scans in TLE patients who are depressed post-operatively and those who develop depression following temporal lobe surgery. This suggests that this region my play in a role in the neurobiological mechanisms predisposing TLE patients the depression commonly seen in this epilepsy syndrome.