Rheumatoid arthritis activity scores in patients with and without fibromyalgia syndrome

BACKGROUND: Fibromyalgia syndrome (FM) is a systemic disease of unknown etiology, which can cause widespread musculoskeletal pain. In patients with rheumatoid arthritis (RA), FM can cause an additional symptom burden, which can affect some variables on the RA disease activity score 28 (DAS28), a tool that evaluates 28 joints in RA patients. OBJECTIVE: Compare the results of four different versions of the DAS28 and the parameters used to determine disease activity scores in RA patients with and without FM, and determine whether there are treatment differences between RA patients with and without FM. DESIGN: Retrospective, cross-sectional. SETTING: Tertiary hospital. PATIENTS AND METHODS: We identified patients diagnosed with RA between 1 September 2016 and 1 February 2020 and identified patients with and without FM. MAIN OUTCOME MEASURES: Differences between variables in the DAS28 calculations (tender joint count [TJC], patient global assessment [PGA], and others), between patients with and without FM, and differences between patients with and without FM who were using or not using biological agents. SAMPLE SIZE: 381, including 322 females (84.5%). RESULTS: The frequency of FM in RA patients was 25.7% (89 females, 24.6%). In RA patients with FM, the TJC and PGA median values were significantly higher than in patients without FM (P<.05). The use of corticosteroids and biological therapy in patients with FM was more frequent than in patients without FM (P<.05). Compared to patients without FM, patients with FM switched treatment more often because of non-response to treatment (P=.01) Median values of the DAS28 scores (calculated by four different versions of the instrument) in RA patients with FM were higher than in patients without FM (P<.05). CONCLUSION: The presence of FM in RA patients may affect the subjective variables in different versions of DAS28 scores, causing the disease activity to score higher on the instrument, erroneously indicating worse disease than is actually present. LIMITATIONS: A single center, retrospective study. CONFLICTS OF INTEREST: None