Sudden Gains in Cognitive Behavioural Therapy and Metacognitive Therapy for Complex Anxiety Disorders.

The present study investigated the prevalence of sudden gains in a large sample of patients with complex anxiety disorders, that is, long-lasting and treatment-resistant anxiety disorders. The properties of these gains were explored in a longitudinal design from two treatment modalities: cognitive behavioural therapy (CBT) and metacognitive therapy (MCT). Participants were 404 adults with a primary diagnosis of anxiety disorder, receiving a standardized 8 weeks of inpatient treatment with CBT or MCT. Symptom severity was measured weekly with the Beck Anxiety Inventory (BAI) and additionally during the first assessment session, pre-treatment, post-treatment and 1-year follow-up. Sudden gains were identified as between-session symptom changes of ≥ 9 points on the BAI, which were relatively large (≥ 25% difference) and stable (did not reverse) in the weeks after the gain. The prevalence of sudden gains during treatment was 19%. Individuals experiencing sudden gains had significantly lower levels of anxiety immediately after treatment and at 1-year follow-up compared to those without. Sudden gains were present in both CBT and MCT, showing similar magnitudes and prevalence, but patients treated with MCT tended to experience sudden gains earlier than those with CBT. This study demonstrates that sudden gains also occur in a long-lasting and treatment-resistant anxiety disorder population treated with CBT and MCT.