Multifocal Pain as a Predictor of Pain Outcomes in Military Veterans with Chronic Musculoskeletal Pain: A Secondary Data Analysis of a Randomized Controlled Trial

Objective. We aimed to examine 1) the relationship between multifocal pain and clinical characteristics, including demographics, pain outcomes, somatic symptoms, health-related quality of life, depression, and anxiety, and 2) whether multifocal pain was independently associated with treatment response. Methods. We conducted a secondary data analysis on veterans with chronic pain enrolled in the Evaluation of Stepped Care for Chronic Pain (ESCAPE) trial with complete data at 9 months (n=222). We examined baseline relationships and used multivariable linear regression to examine whether multifocal pain was independently associated with outcomes that included Brief Pain Inventory (BPI) Interference scale and Graded Chronic Pain Scale (GCPS) scores between baseline and 9 months. Results. The sample had a mean BPI Interference score of 5.362.2 and a mean GCPS score of 65.6613.7, 55% had significant depression (Patient Health Questionnaire 9-item depression scale [PHQ-9] score of ≥10), and 42% had significant anxiety (Generalized Anxiety Disorder Scale [GAD-7] score of ≥10). Veterans reporting three or more pain sites (the "more diffuse pain"group) had significantly less improvement on GCPS (b=4.6, standard error [SE]=2.3, P=0.045), BPI Interference (b=1.0, SE=0.2, P=0.0011), and health-related quality of life (Short-Form 36- item scale, Physical Component Summary) (b=4.1, SE=1.0, P<0.0001) than did veterans reporting fewer than three pain sites (the "less diffuse pain"group). More diffuse pain was not associated with changes in PHQ-9 or GAD- 7 scores. Conclusions. Multifocal pain predicted worse pain outcomes between baseline and 9 months in veterans enrolled in a trial for treating chronic musculoskeletal pain.