The Effect of Obesity on Pain Severity and Pain Interference

Background and objectives: Obesity is one of the most prevalent comorbidities associated with chronic pain, the experience of which can severely interfere with activities of daily living and increase the utilization of clinical resources. Obesity is also a risk factor for increased pain severity (pain intensity) and pain interference (pain related disability). We hypothesize that a higher level of obesity, as measured by body mass index (BMI), would be associated with increased levels of pain severity and interference in a population of chronic pain clinic patients. Methods: Participant data was pulled from a multi-site chronic pain outpatient database from 7/8/2011 to 10/17/2016. The Brief Pain Inventory (BPI), opioid prescriptions, and basic demographic information were queried and we categorized participants into three different ordinal categories based on recorded BMI levels (underweight, normal and overweight, obese). Bivariate analyses were performed to compare pain outcomes by BMI and by other demographic/clinical patient characteristics. Multivariable linear regressions were constructed to model each of four pain severity scores in addition to total pain interference score. All models examined BMI as the primary predictor, controlling for age, receipt of a pain procedure within 45 days prior to the pain clinic encounter, opioid prescription within 45 days prior to the encounter, and diagnosis. The total pain interference model additionally included pain severity (as measured by worst pain in the past 24 hours) as a covariate. Results: 2509 patients were included in the study. The median BMI was 27 and the median age was 59 years. 77% of patients were diagnosed with musculoskeletal pain conditions. Bivariate tests revealed significant differences between BMI groups for all pain severity scores and for total pain interference score. On multivariable modelling controlling for age, pain procedure within 45 days prior to pain clinic encounter, opioid prescription with 45 days prior, and diagnosis, obese patients had significantly higher pain severity (as measured by worst, least, average, and current pain in the past 24 hours) as well as higher pain interference (as measured by the overall pain interference score) than normal weight and overweight patients. Conclusion: In our study of pain clinic patients, obesity was found to be associated with increased pain severity and pain interference. We believe that this relationship is multifactorial and bidirectional. Pain phyisicans should consider the impact of obesity when addressing pain management for patients.