Influence of Depression on Pain and Disability in Patients with Chronic Low Back Pain after Physical Therapy: A Secondary Analysis of a Randomized Controlled Trial

Background. Depressive complications in chronic pain are detrimental to rehabilitation. This study was aimed at determining the influence of the presence of depressive symptoms on the efficacy of physical therapy among participants with chronic low back pain (CLBP). Methods. Data was collected from a randomized controlled trial on 113 participants with CLBP. Participants were reallocated into the depressed or nondepressed groups based on the 50-cutoff point of the self-rating depression scale. All patients received 60 min sessions of physical therapy twice a week for 12 weeks. The primary outcome was back-related disability. Secondary outcomes included pain ratings, sleep quality, life quality, other psychological outcomes, and minimal clinically important differences. These outcomes were collected at baseline, 12, 26, and 52 weeks. Results. 31 (27.4%) were accompanied by depressive symptoms. At 12 weeks, the initial depression score was only associated with anxiety score ( $\beta =1.196$ [0.531 to 1.860], $P=0.001$ ) and depression score ( $\beta =0.742$ [0.200 to 1.284], $P=0.009$ ) in the depressed group, but the initial depression score was associated with anxiety score ( $\beta =0.409$ [0.138 to 0.681], $P=0.004$ ), depression score ( $\beta =0.920$ [0.658 to 1.184], $P<0.001$ ), sleep quality ( $\beta =0.108$ [0.018 to 0.199], $P=0.020$ ), and pain anxiety ( $\beta =0.465$ [0.034 to 0.897], $P=0.035$ ) and negatively associated with life quality ( $\beta =-0.815$ [−1.267 to −0.363], $P=0.001$ ) in the nondepressed group. Conclusions. Physical therapy is effective to CLBP with depressive symptoms. A higher initial depression score may weaken the efficacy of physical therapy in the nondepressed group. Depressive complications may adversely influence intervention efficacy for CLBP. This trial is registered with ChiCTR1800016396.