Discrete Trajectories of Resolving and Persistent Pain in People With Rheumatoid Arthritis Despite Undergoing Treatment for Inflammation: Results From Three UK Cohorts

Abstract

Rheumatoid arthritis (RA) is an example of human chronic inflammatory pain. Modern treatments suppress inflammation, yet pain remains a major problem for many people with RA. We hypothesized that discrete RA subgroups might display favorable or unfavorable pain trajectories when receiving treatment, and that baseline characteristics will predict trajectory allocation. Growth mixture modelling was used to identify discrete trajectories of Short Form-36 bodily pain scores during 3 years in 3 RA cohorts (Early RA Network (n = 683), British Society for Rheumatology Biologics Register Biologics (n = 7,090) and nonbiologics (n = 1,720) cohorts. Logistic regression compared baseline predictor variables between trajectories. The role of inflammation was examined in a subgroup analysis of people with normal levels of inflammatory markers after 3 years. The mean Short Form-36 bodily pain scores in each cohort improved but remained throughout 3 years of follow-up of >1 standard deviation worse than the UK general population average. Discrete persistent pain (59–79% of cohort participants) and resolving pain (19–27%) trajectories were identified in each cohort. In Early RA Network, a third trajectory displaying persistently low pain (23%) was also identified. In people with normal levels of inflammatory markers after 3 years, 65% were found to follow a persistent pain trajectory. When trajectories were compared, greater disability (adjusted odds ratio = 2.3–2.5 per unit baseline Health Assessment Questionnaire score) and smoking history (adjusted odds ratio = 1.6–1.8) were risk factors for persistent pain trajectories in each cohort. In conclusion, distinct trajectories indicate patient subgroups with very different pain prognosis during treatment for RA. Inflammation does not fully explain the pain trajectories, and noninflammatory factors as well as acute phase response predict which trajectory an individual will follow. Targeted treatments additional to those which suppress inflammation might reduce the long-term burden of arthritis pain. PerspectiveImmunosuppression decreases inflammation in RA, but pain outcomes are less favorable. Discrete persistent and resolving pain trajectories were identified after treatment, both in early and established RA. Smoking and greater disability at baseline predicted persistent pain. Identifying patient subgroups with a poor pain prognosis could enable adjunctive treatment to improve outcomes.