A Case of Rapidly Progressive Interstitial Lung Disease with Coexisting Anti-MDA5 and Anti-OJ Antibodies Successfully Treated with Intensive Immunosuppression and Plasma Exchange

Anti-melanoma differentiation-associated gene 5 (MDA5) antibody-positive dermatomyositis is frequently complicated by rapidly progressive interstitial lung disease, whereas anti-aminoacyl-tRNA synthetase (ARS) antibody-positive interstitial lung disease typically follows a subacute or chronic course and responds to immunosuppressive therapy. The coexistence of anti-MDA5 and anti-ARS antibodies, particularly anti-OJ antibodies, is very rare. We report the case of a 58-year-old man who was double positive for anti-MDA5 and anti-OJ antibodies and developed rapidly progressive interstitial lung disease. The disease continued to progress with triple immunosuppressive therapy; however, the introduction of plasma exchange led to marked clinical and radiological improvements. This case highlights the importance of recognizing the coexistence of antibodies and integrating serological, radiological, and clinical findings to guide timely and appropriate treatment.