Effectiveness of a cognitive behavioural intervention for patients with undifferentiated somatoform disorder: results from the CIPRUS cluster randomized controlled trial in primary care

Objective: To examine the effectiveness of a cognitive behavioural intervention delivered by mental health nurse practitioners (MHNPs) to patients with undifferentiated somatoform disorder (USD), compared to usual care. Methods: We conducted a cluster randomized trial among primary care patients with USD comparing the intervention to usual care. The intervention consisted of six sessions with the MHNP. Primary outcome was physical functioning (RAND-36 physical component summary score). Secondary outcomes were the RAND-36 mental component summary score and the eight subscales; anxiety and depression (Hospital Anxiety and Depression Scale) and somatic symptom severity (Patient Health Questionnaire-15). Outcomes were assessed at baseline, 2, 4 and 12 months. We analysed data using linear mixed models by intention-to-treat, and investigated effect modifiers. Results: Compared to usual care (n=87), the intervention group (n=111) showed an improvement in physical functioning (mean difference 2.24 [95% CI 0.51; 3.97]; p=.011), a decrease in limitations due to physical problems (mean difference 10.82 [95% CI 2.14; 19.49]; p.=0.015) and in pain (mean difference 5.08 [95% CI 0.58; 9.57]; p=.027), over 12 months. However effect sizes were small and less clinically relevant than expected. We found no differences for anxiety, depression and somatic symptom severity. Effects were larger and clinically relevant for patients with more recent symptoms and fewer physical diseases. Conclusion: The cognitive behavioural intervention was effective in improving pain and physical functioning components of patients' health. It was particularly suitable for patients with symptoms that had been present for a limited number of years and with few comorbid physical diseases. Trial registration: The trial is registered in the Dutch Trial Registry, www.trialregister.nl, under NTR4686.