Rheumatoid Arthritis Complicated with Anti-melanoma Differentiation-associated Gene 5 Antibody-positive Interstitial Pneumonia.

Anti-melanoma differentiation-associated gene 5 (MDA5) antibodies are frequently detected in amyopathic dermatomyositis with rapidly progressive interstitial lung disease (RP-ILD). However, the presence of anti-MDA5 antibodies in other connective tissue diseases is not well known. We herein report a case of rheumatoid arthritis complicated with refractory anti-MDA5 antibody-positive ILD. A 75-year-old Japanese woman was referred to our hospital for refractory ILD. Serological testing was positive for anti-MDA5 antibody without any muscle or skin lesions. Immunosuppressive therapy (prednisolone and tacrolimus) ameliorated her symptoms as well as ILD. Anti-MDA5 antibody-positive ILD, as well as dermatomyositis with RP-ILD, can occur in patients with rheumatoid arthritis.