Predictors and moderators of symptom change during cognitive-behavioral therapy or supportive psychotherapy for body dysmorphic disorder

Background: Research on predictors of treatment outcome in body dysmorphic disorder, a common and severe disorder, is very limited, and no prior studies have examined moderators of outcome. Because treatment is often but not always efficacious, it is important to identify who is more likely to benefit. We examined predictors and moderators of improvement with therapist-delivered cognitive-behavioral therapy versus supportive psychotherapy in the only study of these treatments for body dysmorphic disorder. This report presents secondary analyses from a study whose primary findings have previously been published (Wilhelm et al., 2019). Methods: Participants (N=120) with DSM-IV body dysmorphic disorder were randomized to therapist-delivered weekly cognitive-behavioral therapy or supportive therapy for 24 weeks. Using reliable and valid measures, we tested baseline body dysmorphic disorder severity, insight/delusionality, and depression severity as predictors and moderators of overall and treatment modality-specific symptom change. We explored additional variables as predictors and moderators of outcome. Results: Greater treatment credibility (p=0.02) and presence of obsessive-compulsive personality disorder (p=0.03) predicted greater improvement. Serotonin-reuptake inhibitor treatment at baseline (unchanged during the study) (p=0.01) predicted less improvement. No other variables predicted or moderated outcome (all p>0.05). Limitations: The study was not powered a priori to detect predictor or moderation effects, which limited our ability to detect them unless they were strong. Conclusions: Because greater treatment credibility predicted better outcomes, fostering credibility during therapy may maximize gains. Improvement was not impeded by more severe body dysmorphic disorder, depressive symptoms, or poorer insight. No variables moderated treatment-specific improvement.