Fibromyalgia in patients with rheumatoid arthritis. A 10-year follow-up study, results from the Oslo Rheumatoid Arthritis Register.

Objectives: To examine cross-sectional and longitudinal relationships between fibromyalgia (FM) and rheumatoid arthritis (RA) disease activity.

Methods: 636 patients in the observational Oslo RA register (ORAR) were invited to a clinical examination in 1999. 28-tender and swollen joint counts (TJC, SJC) and 18-tender points were assessed, the RA disease activity score (DAS-28) calculated. Fibromyalgia (FM) was diagnosed according to 1990 (FM-1990) and modified 2011 (mFM-2011) ACR criteria. At the 10-year follow-up patients completed the RA Disease Activity Index (RADAI) and Routine Assessment of Patient Index Data 3 (RAPID-3). Baseline and 10-year RA disease activity were compared across presence/absence of FM. Linear regression models were constructed with 10-year RADAI and RAPID-3 as outcome.

Results: 502 patients participated at baseline data-collection and 10-year data was available in 236. At baseline, mean (SD) age was 59.5 (12.5) years and 87% were female. 9% and 30% had FM-1990 and mFM-2011 respectively. RA-FM patients were predominantly female with higher SJC, TJC, and DAS-28 at baseline. Baseline RA-FM predicted higher levels of RADAI and RAPID-3 at the 10-year follow-up.

Conclusions: RA-FM was associated with significantly higher levels of cross-sectional and longitudinal RA disease activity. FM should be considered in patients with RA not reaching remission.