Recent Knowledge Regarding the Epidemiology, Exacerbating Factors, and Treatment of Rheumatoid Arthritis Complicated by Interstitial Lung Disease

Rheumatoid arthritis (RA) is a systemic rheumatic disease. Its most prominent characteristic is synovitis, which manifests clinically as arthritis, resulting in joint damage. Interstitial lung disease (ILD) is an extraarticular manifestation of RA that hinders therapeutic goals, affects life prognosis, and can be worsened by the administration of disease-modifying antirheumatic drugs (DMARDs). Therefore, proper management of ILD, including consideration of risk factors such as the systemic disease activity of RA and autoantibodies, and early detection with high-resolution computed tomography are required at the introduction of DMARDs. Methotrexate, a class of DMARD used as the anchor drug for RA treatment, has been recognized as likely to worsen RA-ILD. However, there are currently reports suggesting that methotrexate may have beneficial effects on RA-ILD. Conversely, several studies have also shown exacerbations of ILD with the administration of biological DMARDs, which are thought of as tolerable for patients with RA-ILD. Rheumatologists should be wary of emergence or changes in the activity of ILD and arthritis during treatment of any kind with DMARDs. Further studies are warranted to clarify underlying ethnic factors, such as the possible effects of antimelanoma differentiation-associated gene 5 antibodies on RA-ILD.