Distinctive Clinical Characteristics and Outcome of ILD-Onset Rheumatoid Arthritis and ACPA-Positive ILD: a Longitudinal Cohort of 282 Cases.

The aim of this study is to investigate the clinical features and outcome of interstitial lung disease (ILD)-onset rheumatoid arthritis (RA) and anti-citrullinated protein antibody (ACPA)-positive ILD-only patients. Arthritis-onset and ILD-onset RA-ILD and ACPA-positive ILD-only patients consecutively admitted to Peking Union Medical College Hospital from January 2008 to December 2017 were enrolled and followed-up. Their demographic, clinical, and laboratory features as well as outcome were collected and analyzed. Compared with arthritis-onset RA-ILD (n = 166, median arthritis-to-ILD interval: 60 months), the ILD-onset RA-ILD (n = 75, median ILD-to-arthritis interval: 2 months) had less rheumatoid nodules and higher titer of ACPA, and manifested more stable ILD (median estimated progression-free survival: 120 vs. 100 months, p = 0.019). Elder age (≥ 65 years) at ILD diagnosis and UIP pattern were associated with ILD progression by both univariate and Cox hazards modeling analysis (p < 0.05). In ACPA-positive ILD-only patients (n = 41), arthritis developed in 7 (17.1%) female patients after a median interval of 24 months. ACPA-positive ILD who subsequently developed arthritis exhibited higher frequency of rheumatoid factor (RF), higher titer of ACPA, and higher levels of ESR and CRP (p < 0.05). Multivariate regression analysis showed that positive RF (OR 12.55, 95% CI 1.31 to 120.48) was the independent risk factor for arthritis development in ACPA-positive ILD-only patients. ILD-onset RA-ILD had more stable ILD compared with arthritis-onset RA-ILD. ACPA-positive ILD patients with positive RF are at increased risk of developing RA.