Fibromyalgia and the Prediction of Two-Year Changes in Functional Status in Rheumatoid Arthritis Patients

Objective: Previous cross-sectional studies have shown that rheumatoid arthritis (RA) patients with fibromyalgia (FM) have higher disease activity, greater medical costs, and worse quality of life compared to RA patients without FM. We determined the impact of FM on 2-year changes in the functional status of RA patients in a prospective study. Methods: Subjects included participants in the Brigham Rheumatoid Arthritis Sequential Study who were enrolled in a substudy of the effects of pain in RA. Subjects completed questionnaires, including the Multi-Dimensional Health Assessment Questionnaire (MDHAQ) and Polysymptomatic Distress (PSD) scale, semiannually, and underwent physical examination and laboratory tests yearly. Results: Of the 156 included RA subjects, 16.7% had FM, while 83.3% did not. In a multivariable linear regression model adjusted for age, sex, race, baseline MDHAQ score, disease duration, rheumatoid factor/cyclic citrullinated peptide antibody seropositivity, disease activity, and psychological distress, RA patients with FM had a 0.14 greater 2-year increase in MDHAQ score than RA patients without FM (P = 0.021). In secondary analyses examining the association between continuous PSD scale score and change in MDHAQ, higher PSD scale scores were significantly associated with greater 2-year increases in MDHAQ score (β coefficient 0.013, P = 0.011). Conclusion: Both the presence of FM and increasing number of FM symptoms predicted worsening of functional status among individuals with RA. Among individuals with RA and FM, the magnitude of the difference in changes in MDHAQ was 4- to 7-fold higher than typical changes in MDHAQ score among individuals with established RA.