Factors associated with interstitial lung disease and the progressive fibrosing phenotype in rheumatoid arthritis-related interstitial lung disease.

Background: The risk factors for interstitial lung disease (ILD) in rheumatoid arthritis (RA) are inconsistent among previous studies. Furthermore, the factors associated with the emergence of the recently defined progressive fibrosing (PF) phenotype are unknown. Herein, we analyze the risk factors for ILD in RA. We also analyze the factors associated with a PF phenotype. Methods: We collected the clinical and laboratory details of subjects with RA with (cases) or without (controls) ILD. Scoring of high-resolution computed tomography (HRCT) features of ILD was performed. We identified the subgroup that developed the PF phenotype during follow-up. We analyzed the factors associated with ILD using logistic regression (primary objective). We also compared the characteristics of ILD subjects with or without the PF phenotype (secondary objective). Results: We included 60 subjects (30 cases, 30 controls). Subjects with ILD had higher age, lower body mass index, longer duration of RA, and poorer lung function than the controls. Age (p = 0.007) and the duration of RA (p = 0.049) were the only significant predictors of ILD on univariate and multivariate analysis, respectively. Six (20%) subjects with RA-ILD developed a PF phenotype. These subjects were older, had greater frequency of honeycombing, and higher HRCT scores for honeycombing and aggregate fibrosis than those without the PF phenotype. Among subjects with honeycombing, 41.7% developed the PF phenotype. Conclusions: RA-ILD was associated with the duration of RA and age. Subjects with the PF phenotype were older and had higher honeycombing and fibrosis scores on HRCT chest.