Mechanisms of Change in Cognitive Behavioral Therapy for Body Dysmorphic Disorder.

Although cognitive-behavioral therapy (CBT) is highly efficacious for body dysmorphic disorder (BDD), not all patients benefit, and mechanisms underlying response remain unknown. In this first report of the mechanisms underlying improvement with CBT for BDD, we examined whether cognitive (maladaptive beliefs, perfectionism, schemas) and behavioral (checking, grooming, avoidance behaviors) changes mediate the effect of CBT on BDD symptom reduction. Forty-five participants with BDD who enrolled in a CBT for BDD treatment development study were included in two sets of analyses: (1) between-subject mediation of the effect of 12 weeks of CBT versus waitlist, and (2) within-subject mediation of longitudinal change in BDD symptom severity during 24 weeks of CBT. No significant mediators emerged in the between-subject analysis. Checking, grooming, avoidance behaviors, and maladaptive beliefs mediated within-subject improvements over time. Findings suggest that BDD symptom reduction occurs through the very mechanisms that have been hypothesized to maintain BDD in CBT models. Targeting certain cognitive (beliefs about appearance) and behavioral (checking, grooming, and avoidance behaviors) mechanisms in future treatment trials may enhance symptom improvement during CBT. # NCT00106223.