Predictors of Pain Outcomes in Patients with Chronic Musculoskeletal Pain Co-morbid with Depression: Results from a Randomized Controlled Trial

Objective. The combination of chronic musculoskeletal pain and depression is associated with worse clinical outcomes than either condition alone. In this study, we report the predictors of pain intensity and activity interference in primary care patients with co-morbid pain and depression. Methods. This is a secondary data analysis of the 250 persons who participated in a randomized clinical trial designed to test the effectiveness of 12 weeks of optimized antidepressant therapy for both depression and pain. Using multivariate linear regression analysis, we assessed the predictive value of baseline self-efficacy, fear of movement, pain beliefs, and demographic and clinical factors on 3-month Graded Chronic Pain Scale pain intensity and activity interference outcomes. Results. In the full model, significant sociodemographic predictors of less activity interference included being non-white (beta -5.8, P = 0.04) and being employed (beta -13.3, P < 0.0001). The latter was also predictive of less pain intensity (beta -5.6, P = 0.01). As expected, the optimized antidepressant treatment arm was associated with improved outcomes (pain intensity: beta -3.7, P = 0.0005 and activity interference: beta -6.4, P = 0.01). Whereas stronger perceived pain control (beta 3.6, P = 0.01) was associated with greater activity interference, higher degree of fear of movement (or fear avoidance) predicted greater pain intensity (beta 0.46, P = 0.04) and activity interference (beta 0.57, P = 0.05). Neither the location (low back vs hip/knee) nor duration of pain were predictive of pain intensity or interference outcomes. Conclusion. The findings are consistent with a bio-psychosocial model, implicating the need to consider the impact of sociodemographic variables and pain-related beliefs and cognition on pain-related outcomes for patients with co-morbid musculoskeletal pain and depression.