Both Explained and Unexplained Physical Symptoms Reduce the Effectiveness of Treatment for Depression in Primary Care

Aim: to assess to what extent clinically significant concomitant physical symptoms influence the effect of treatment for major depression, and whether or not this relationship is explained by actual co morbid medical conditions. Method: Pre-planned secondary data-analysis on a one-year cluster-randomized trial in primary care, comparing the effectiveness of collaborative care with care as usual (CAU). Depression was measured using the PHQ9. The number of physical symptoms was measured with the Physical Symptoms Questionnaire (PSQ) at baseline. Multilevel logistic regression models were used to test whether physical symptoms predicted lack of response to treatment, adding interaction terms to test differential effects on collaborative care versus CAU. Results: Concomitant physical symptoms negatively influenced the response to treatment for collaborative care and care as usual, but the effect was the same for both conditions (there was no interaction). Therefore, collaborative care for depression is still more effective than CAU for patients with concomitant physical symptoms, but these patients have lower odds on response to treatment regardless of treatment condition. Specifically, physical symptoms predicted a lack of response in both treatment conditions The time to first treatment response was 4.3 months longer for the group suffering from concomitant physical symptoms. The results were not explained by the presence of chronic physical illness. Conclusion: In this RCT, patients with MDD and concomitant physical symptoms benefited less from treatment for MDD in primary care, regardless of the type of treatment (either collaborative care or CAU). Whether or not these physical symptoms were due to a comorbid medical condition did not explain the results. Further research is needed to improve treatment for MDD with concomitant physical symptoms, but in the mean time there is no reason not to apply collaborative care for patients suffering from both depression and physical symptoms.