Evidence for a biopsychosocial influence on shoulder pain: pain catastrophizing and catechol-O-methyltransferase (COMT) diplotype predict clinical pain ratings.

The experience of pain is believed to be influenced by social, cultural, environmental, psychological, and genetic factors. Despite this assertion, few studies have included clinically relevant pain phenotypes when investigating interactions among these variables. This study investigated whether psychological variables specific to fear-avoidance models and catechol-O-methyltransferase (COMT) genotype influenced pain ratings for a cohort of patients receiving operative treatment of shoulder pain. Patients (n=58) completed questionnaires and had COMT genotype determined pre-operatively. Then, shoulder pain ratings were collected 3-5 months post-operatively. This cohort consisted of 24 females and 34 males, with mean age of 50.3 (SD=15.0) and pre-operative pain rating of 4.5/10 (SD=1.8). The frequency of COMT diplotypes was 34 with "high COMT activity" (LPS group) and 24 with "low COMT activity" (APS/HPS group). Preliminary analysis indicated that of all the fear-avoidance variables considered (fear of pain, kinesiophobia, pain catastrophizing, and anxiety), only pain catastrophizing was a unique contributor to clinical pain ratings. A hierarchical regression model indicated that an interaction between pain catastrophizing and COMT diplotype contributed additional variance in pre-operative pain ratings. The pain catastrophizingxCOMT diplotype interaction demonstrated predictive validity as patients with high pain catastrophizing and low COMT activity (APS/HPS group) were more likely (RR=6.8, 95% CI=2.8-16.7) to have post-operative pain ratings of 4.0/10 or higher. Our findings suggest that an interaction between pain catastrophizing and COMT diplotype has the potential to influence pain ratings in patients seeking operative treatment of their shoulder pain.