Abstracts

Rationale: The importance of recognizing, treating and understanding depression in patients with epilepsy is acknowledged but has yet to be translated into practice. Abnormalities in limbic structures in the medial temporal lobe occur in depressed patients with temporal lobe epilepsy (TLE), as well as in depressed patients without epilepsy. The neural correlates of depression in patients with other types of epilepsy has not been well studied. We utilized MRI morphometric assessment to identify cortical regions associated with depressive symptoms in patients with focal epilepsy whose seizure foci were located outside the medial temporal lobe. For comparison, patients with TLE and healthy controls were also studied. Methods: 21 patients with extratemporal (ET) epilepsy (7 frontal or frontal-temporal; 6 parietal or parietal-occipital; 8 multifocal), 36 patients with TLE, and 45 normal controls (NC) completed a Beck Depression Inventory (BDI) and underwent a high-resolution research MRI. Scanning was performed at either the NYU Center for Brain Imaging or UCSD Radiology Imaging Laboratory. Acquisition parameters were optimized for increased gray/white matter image contrast. Image processing and analysis utilized the FreeSurfer software package. Cortical thickness was measured using automated procedures that segment the cortex and measure distance between the pial surface and gray/white matter boundary. For each hemisphere, a general linear model estimated the effects of BDI score on cortical thickness at each vertex along the cortical surface. The correlation between BDI score and cortical thickness was assessed within and between each subject group (ET, TLE, NC). Results were mapped onto an average brain surface and thresholded at p<.0005 Results: In ET patients, BDI score correlated negatively with thickness of left lateral orbitofrontal cortex (L LOFC) and R precentral and temporo-parietal cortex. In a comparison between ET and TLE patients, the correlation between BDI and cortical thickness differed in L LOFC and L frontal pole; for both regions, the BDI-thickness correlation was negative in ET and positive in TLE. Figure 1 shows the correlation of L LOFC thickness and BDI score in ET and TLE patients, as well as healthy controls. There is a negative correlation between BDI and L LOFC thickness in ET patients and NC subjects, as compared to a positive correlation in TLE patients. Conclusions: In patients with extratemporal partial epilepsy, as well as in healthy controls without epilepsy, increasing severity of depressive symptoms was associated with L LOFC thinning. In contrast, patients with TLE had L LOFC thickening in association with increased depression. The OFC is a brain region involved in emotional regulation and reward processing previously implicated in depression. These preliminary results suggest that the neural basis of depression in patients with extratemporal epilepsy is similar to that in people without epilepsy, while depression in TLE may be different.