Anti-MDA5 Positive Dermatomyositis Overlapping with Rheumatoid Arthritis: A Case Report.

We report a rare case of overlap syndrome between anti-MDA5-positive dermatomyositis (DM) and rheumatoid arthritis (RA) in a 65-year-old woman. Initially diagnosed with RA, the patient later developed characteristic DM manifestations including characteristic DM rash, generalized weakness, poor appetite, and unintentional weight loss. Laboratory findings revealed elevated muscle enzymes, positive anti-melanoma differentiation-associated gene 5 (MDA5) antibody and anti-Ro52 antibodies, and increased anti-citrullinated protein antibodies. The patient showed significant improvement following combination therapy with prednisone and mycophenolate mofetil, highlighting the importance of early recognition and appropriate management of this rare overlap syndrome.