Background Pain is common in rheumatoid arthritis (RA), and a significant portion of patients report pain also after adequate disease suppression and achievement of low detectable inflammation. In order to optimize pain and antirheumatic treatment, there is a need for early identification of patients with pain that is independent of inflammation.
Objectives To investigate the prevalence and potential predictors for a severe persistent pain phenotype of early RA.
Methods We used the cases from a Swedish population-based case-control study; the EIRA study; in total, 1802 incident RA patients aged 18-70 was recruited 1996-2009 and followed in the Swedish Rheumatology Quality register for up to 5 years. We defined RA severe persisting pain phenotype as having pain measured on a visual-analog scale (VAS) ≥50 at diagnosis and VAS ≥50 together with a CRP <10 at the 2-year follow-up visit. Logistic regression was used to calculate the effect of sex, age at diagnosis and calendar period of diagnosis on this outcome, we also further adjusted our model for smoking and socioeconomic status (based on education).
Results Out of 1733 patients with data on both time points we found 123 patients (7.1%) with severe pain persisting phenotype. Sex and calendar period of diagnosis did not affect this condition significantly, but age at diagnosis did. Compared to the reference group (aged 50-60) the oldest age group (aged 65-70) had a lowered risk (OR=0.54 [95%CI: 0.29-1.00]), also for the youngest patients (aged <40), there was an indication of a lower risk, albeit not statistically significant (OR=0.58 [95%CI: 0.33-1.04]). Further adjustments for smoking and socioeconomic status enhanced the effect of older age (for patients aged 65-70 the OR=0.46 [95%CI: 0.24-0.90], smoking and socioeconomic status were not significant predictors themselves. There were no significant differences between the age groups concerning pain at diagnosis or correlation between pain and DAS28, either at diagnosis or after 2 years.
Conclusions In a population-based cohort of early RA patients, the prevalence of severe persisting pain was 7.1%. Older patients seem to have a lower risk for development of severe persisting pain in early RA, independent of sex, calendar period of diagnosis, smoking and socioeconomic status. These data indicate that age is important to consider in further investigations of non-inflammatory coupled pain development in RA.
Disclosure of Interest : None declared