The Moderating Effect of Obesity on Cognitive-Behavioral Pain Treatment Outcomes

Objective. To assess the effects of body mass index on cognitive-behavioral pain treatment outcomes for chronic low back pain. Design. Retrospective analyses of data from a clinical trial were performed, with body mass index used to divide patients into obese and non-obese groups for comparison. Setting. VA medical center outpatient clinic. Patients. Veterans (N = 74) receiving outpatient care through the VA. Interventions. Delivery of a 10-week cognitive-behavioral pain treatment intervention. Outcome Measures. The Numerical Rating Scale (pain intensity), Roland Morris Disability Questionnaire (disability), Veteran's SF-36 (health-related quality of life), and Beck Depression Inventory (emotional functioning) were administered pre- and post-treatment. Results. The study included 42 obese and 32 non-obese participants, most of whom were male (89%). The average body mass index was 32.44 kg/m(2), with average pain intensity rated as 6.59 out of 10. There were no pre-treatment differences in outcome measures between the groups. Repeated measures ANOVAs revealed main effects of Time on all but one outcome (Mental Component score), indicating that the cognitive-behavioral interventions were largely effective. However, Time-body mass index (BMI) group interactions revealed that non-obese participants showed greater improvement following treatment than did their obese counterparts on measures of disability (P < 0.05), physical aspects of quality of life (P < 0.01), and emotional functioning (P < 0.05). Conclusions. Standard cognitive-behavioral pain treatment did not yield comparable outcomes for obese and non-obese participants. Results suggest a potential moderating role of BMI in low back pain outcomes. Future work with other pain conditions, including examination of potential mechanisms through which BMI impacts treatment outcomes, is recommended.