What makes cognitive behavior therapy work? An investigation of psychological and inflammatory processes

Background: Common mental disorders (CMDs; anxiety disorders, depression, insomnia and stress-related disorders) cause significant suffering, reduced functioning and impaired quality of life. Cognitive behavior therapy (CBT) is an effective treatment, but there is considerable room for improvements in outcomes. Increased knowledge regarding potential mechanisms of change in CBT could inform treatment development. Investigation of both psychological and inflammatory processes could be one way of moving the field forward. Aims: The aim of this thesis was to investigate processes and correlates of therapeutic change in CBT for CMDs. Based on two clinical trials set in primary care in which CBT for CMDs were tested (Study I and II), this thesis investigated mediators of change in CBT for exhaustion disorder (Study III), processes of change in CBT for social anxiety disorder (Study IV), and inflammatory correlates of change in CBT for CMDs (Study V). Methods: In the clinical trials (Study I, N = 211; and Study II, N = 396), primary care patients with CMDs were treated with CBT, delivered in different formats. Based on the effects found in these trials, further analyzes were conducted in Study III, IV and V, with regard to processes related to outcome. In Study III, mediators of change were analyzed in patients with a primary exhaustion disorder (N = 82), randomized to CBT or another active psychological treatment. In Study IV, the effect of changes in proposed maintaining processes were analyzed in relation to symptom change in guided self-help CBT for social anxiety disorder (N = 61). In Study V, inflammatory cytokines were measured before and after treatment with CBT and analyzed in relation to psychiatric symptoms (N = 367). Results: The results of the clinical trials (Study I and II) showed beneficial effects of disorder-specific CBT for CMDs. In Study III, CBT led to larger effects on symptoms of exhaustion than the comparator, and this difference in effects was mediated by improvements in sleep quality and perceived competence. In Study IV, several of the putative change processes (i.e., estimated probability and cost of negative social events, self-focused attention, avoidance, and safety behaviors) predicted subsequent changes in social anxiety. However, all of these processes except for avoidance were also predicted by prior symptom reduction. In Study V, we found no robust associations across the study sample between inflammatory cytokines and psychiatric symptom severity. Further, the marked symptom improvement was not tracked by reductions in cytokines. Conclusions: CBT for patients with CMDs in primary care yielded favorable effects on psychiatric symptoms. In CBT for exhaustion disorder, sleep disturbance and perceived competence may be important treatment targets. In social anxiety disorder, several of the proposed maintaining processes seem to be part of positive reciprocal cycles, where improvements in processes and symptoms influence each other. Avoidance showed a unidirectional effect on subsequent symptoms and might thus be of specific clinical relevance. The results also suggest a limited role of inflammatory processes in symptomatic improvements following CBT for CMDs