Comorbid fibromyalgia is independently associated with multidimensional PROMIS outcomes in rheumatoid arthritis and systemic lupus erythematosus: a cross-sectional comparative study

Objectives To evaluate the association between fibromyalgia and multidimensional patient-reported symptom burden measured by PROMIS in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), and to compare these associations with those observed for disease activity. Methods In this cross-sectional study, 201 patients (RA n = 100; SLE n = 101) completed PROMIS short-form instruments assessing physical function, pain intensity, pain interference, fatigue, sleep disturbance, anxiety, and depression. Fibromyalgia was ascertained using the 2016 ACR Fibromyalgia Diagnostic Criteria. Disease activity was evaluated using the 28-joint Disease Activity Score (DAS28-ESR) in RA and the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2 K) in SLE. Multivariable linear regression models were used to assess independent associations. Results PROMIS profiles were largely comparable between RA and SLE, with SLE demonstrating better physical function (35.8 ± 7.9 vs 32.1 ± 6.7, p < 0.001). In both diseases, the presence of fibromyalgia was associated with significantly worse PROMIS scores across most domains. In adjusted models, fibromyalgia remained independently associated with higher pain intensity (RA β = 5.19, p < 0.001; SLE β = 6.31, p < 0.001), greater fatigue (RA β = 6.94, p < 0.001; SLE β = 7.50, p < 0.001), higher anxiety (RA β = 5.25, p = 0.007; SLE β = 6.24, p = 0.01), and higher depression scores (RA β = 6.79, p < 0.001; SLE β = 6.61, p = 0.009). Fibromyalgia was also independently associated with poorer physical function in both diseases (RA β = −3.06, p = 0.012; SLE β = −5.99, p < 0.001). Associations were consistent across domains and of greater magnitude than those observed for disease activity. Conclusion Fibromyalgia was independently associated with substantially worse multidimensional PROMIS outcomes in both RA and SLE, stronger associations than disease activity across several PROMIS domains.