Mechanisms of change in long-term transdiagnostic cognitive behavioural therapy: the sequential effect of rumination and worry on symptoms and quality of life.

Anxiety and depressive disorders are the most prevalent disorders worldwide and significantly impair quality of life (QoL). Transdiagnostic cognitive behavioural therapy (TD-CBT) is effective in treating these disorders and improving QoL, but its long-term mechanisms of change are poorly understood. Rumination and worry are key processes addressed by TD-CBT. In this study, we analysed the sequential effect of TD-CBT on post-treatment rumination and worry, anxiety/depression symptoms at 6-months and psychological and physical QoL at 12-months. We use data from PsicAP, a randomised clinical trial in the Primary Care (PC) setting, with 1061 participants randomised to TAU (treatment as usual) or TD-CBT+TAU. Path analyses using SEM were employed to test serial mediation models. Analyses indicated that TD-CBT exerts its long-term beneficial effects on QoL through a cascade of effects, whereby first the maladaptive cognitive processes of rumination and worry are reduced (post-treatment), then anxiety and depressive symptoms (6-months) and finally QoL is improved (12-months). This study provides longitudinal evidence on the mechanisms of change of TD-CBT in patients with anxiety and depression. It also highlights the importance of targeting transdiagnostic interventions towards early modification of negative repetitive thought processes as a critical pathway to long-term symptomatic and functional recovery.