Detecting respiratory impairment in newly diagnosed rheumatoid arthritis by MRC dyspnoea scale and microfibrillar-associated protein 4.

Objectives: To evaluate the Medical Research Council (MRC) dyspnoea scale and serum Microfibrillar-associated protein 4 (MFAP4) levels for the detection of respiratory impairment in newly diagnosed rheumatoid arthritis (RA).

Methods: Patients underwent blood tests, pulmonary function tests (PFT) and dyspnoea assessment using the MRC scale. Respiratory impairment was defined as a diffusion capacity of the lungs for carbon monoxide (DLCO) <80% predicted or FEV1/FVC <70%. The primary outcomes were the MRC and MFAP4's sensitivity, specificity, and diagnostic odds ratio (DOR) with 95% confidence intervals (CI).

Results: One hundred and thirty-one patients had available baseline tests. Mean age was 57.7 years (SD: 10.9), 61% were female, and 45% had respiratory impairment. For MRC score ≥ 2, the sensitivity was 39.0% (95% CI 26.5; 52.6), specificity 76.4% (95% CI 64.9; 85.6), and DOR 2.07 (95% CI 0.97; 4.40). For MFAP4 > 29.0 U/mL, the sensitivity was 62.7% (95% CI 49.1; 75.0), specificity 56.9% (95% CI 44.7; 68.6), and DOR 2.22 (95% CI 1.10; 4.50). The DOR was 3.01 (95% CI 1.27; 7.16) for MFAP4 detecting respiratory impairment when adjusted for age, sex and smoking status.

Conclusion: The MRC dyspnoea score and unadjusted MFAP4 levels were poor predictors of respiratory impairment in patients with early treatment-naïve rheumatoid arthritis.