Predictors of unacceptable pain and the impact of sociodemographic factors and comorbidities—results from a large, nationwide cohort of early rheumatoid arthritis

Abstract

Objectives: The purpose of this paper is to investigate baseline predictors of unacceptable pain, overall and in patients with low inflammatory activity, as well as of pain over time, in patients with early rheumatoid arthritis (RA). Methods: We studied patients newly diagnosed with RA in Sweden in 2012-2020 (N = 10297), using data from several national registers. Pain was assessed by a Visual Analogue Scale (VAS; 0-100 mm). Unacceptable pain was defined as VAS pain > 40 mm, and low inflammation as C-reactive protein < 10 mg/L. Baseline predictors of unacceptable pain and unacceptable pain with low inflammation were evaluated using logistic regression analysis. Predictors of pain over time, from baseline to the 2-year follow-up, were investigated using linear mixed-effect models. Results: Of the 3427 patients with data at 2 years, 1143 (33%) had unacceptable pain, and 808 (26%) had unacceptable pain with low inflammation. Female sex, worse patient-reported outcomes (PROs), low parameters of inflammation, and having many tender compared with swollen joints were baseline predictors of unacceptable pain and unacceptable pain with low inflammation at 1 and 2 years, and of more pain over time. Smoking, non-European origin, and having a psychiatric or pain-related comorbidity were also associated with more pain over time. Conclusions: Factors beyond inflammation contribute significantly to unacceptable pain at follow-up in RA. Physicians should be aware of the increased risk of unacceptable pain in patients with worse PROs and with discrepancies between the number of tender and swollen joints. Sex and cultural differences also need to be considered in future pain interventions in early RA.