FDG-PET predictors of response to behavioral versus pharmacotherapy in OCD

Prior investigators have used FDG-PET to identify cerebral metabolic predictors of treatment response in OCD patients. Two research groups have found that higher orbitofrontal and basal ganglia metabolism on pretreatment scans predicted poorer response to pharmacotherapy. One of these groups also found that higher R anterior cingulate metabolism predicted poorer response to pharmacotherapy. However, differential FDG-PET predictors of treatment response to behavioral therapy versus pharmacotherapy have not yet been reported. Therefore, we examined pretreatment FDG-PET images of 18 OCD patients treated with behavioral therapy and 20 OCD patients treated with pharmacotherapy (either fluoxetine or paroxetine). In patients treated with behavior modification, the pretreatment ratio of activity in L orbital cortex to L anterior cingulate gyrus predicted treatment outcome (stepwise variable selection, F=4.64; df= ; p=.047), with a higher ratio predicting better treatment response. Further, this ratio correlated significantly (r=.63; p=.005) with percent change in the Obsession Items on the Y-BOCS. Data for the patients treated with SRI medication are still being analyzed, but preliminary analysis suggests that metabolic activity in L orbital cortex is inversely correlated with treatment response. Though this study is limited by the fact that assignment to treatment groups was not random, our finding in behavior therapy treated patients suggests that relatively high metabolism in the L anterior cingulate gyrus (and its related circuitry) may be a marker for a patientʹs inability to fully engage in this therapy. Our finding in medication treated patients supports previous work.