Objective: To identify clinical and genetic risk factors for interstitial lung disease (ILD) or airway disease (AD) in patients with rheumatoid arthritis (RA) and to evaluate differences between the associations of these factors with ILD and AD.
Methods: We reviewed high-resolution computed tomography (HRCT) images and clinical data of 356 RA patients obtained at their first visit. The diagnosis of ILD and AD was based on abnormal HRCT findings. Multinomial logistic regression analysis and likelihood ratio tests were performed.
Results: High titers of rheumatoid factor are similarly associated with increased risks of ILD (relative risk ratio, 3.1; p = 0.02) and AD (relative risk ratio, 3.0; p = 0.02). High levels of anti-cyclic citrullinated peptide antibodies were associated strongly with AD (relative risk ratio, 3.8; p = 0.005) and less strongly with ILD (relative risk ratio, 2.7; p = 0.07). Age was the potent risk factor for ILD (relative risk ratio, 4.6; p = 0.003), while that for AD was advanced stage (relative risk ratio, 11.5; p < 0.0005). The carriage of HLA-DRB1*1502 had opposite influences on the two conditions: relative risk ratio = 4.02 for ILD (p = 0.013) and relative risk ratio = 0.15 for AD (p = 0.08). This difference was statistically significant (p = 0.0005). Associations of sex and smoking history with ILD disappeared in the multinomial logistic regression analysis.
Conclusions: The differential associations of ILD and AD with various clinical and genetic factors suggest that ILD and AD have distinct etiologies in RA.
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