LAUSR

Background In patients with rheumatoid arthritis (RA), erosive arthritis is a major determinant of long-term prognosis. Seropositivity for immunoglobulin (Ig) M rheumatoid factor (RF) or cyclic citrullinated peptide antibodies (anti-CCP) are risk factors for erosive arthritis. However, RA patients can also present IgA RF. The risk for erosive arthritis associated with RF IgA seropositivity is not established. Objectives To evaluate the risk for erosive arthritis associated with IgA RF seropositivity in RA patients. Methods Cross-sectional observational study, including RA patients (fulfilling the 2010 ACR/EULAR classification criteria) and consecutively observed in a hospital-based rheumatology outpatient clinic, from April to August 2017. At time of inclusion, patient characteristics were evaluated, including: gender, age, RA duration since time of diagnosis, smoking habits, seropositivity for IgA RF, IgM RF and anti-CCP, erosive arthritis in hand and feet X-rays. Risk association for erosive arthritis was analysed with univariate and multivariable logistic regression models for the putative risk factors and confounders. Odds ratios (OR) and 95% confidence intervals (CI) of IgM RF, IgA RF, and anti-CCP seropositivity for erosive arthritis were estimated. Statistical significance was set at 0.05. Results 86 patients were included. The univariate logistic regression showed significant positive associations of IgA RF, IgM RF and anti-CCP with erosive arthritis. In the multivariate analyses, adjusting for confounders (gender, age, disease duration and smoking), the OR for erosive arthritis associated with IgA RF, IgM RF and anti-CCP were respectively: OR=2.42 (95% CI 0.72–8.07; p=0.152); OR=3.54 (95% CI 1.16–10.83; p<0.05); OR=4.13 (95% CI 1.33–12.82; p<0.05). The seropositivity for IgM RF, IgA RF and anti-CCP were strongly associated among each other (Chi-square test with p<0.001 for all associations). Conclusions In this RA cohort, the IgA RF was associated with erosive arthritis in univariate analysis, but did not prove to be an independent risk factor in multivariate regression, due to its strong association with IgM RF and anti-CCP. Determination of IgA RF does not seem to add predictive value for erosive arthritis in RA patients. Disclosure of Interest None declared