A Case of Adult-Onset Still Disease Masquerading as Dermatomyositis

Adult-onset Still disease (AOSD) is a systemic autoinflammatory disorder characterized by quotidian fevers, arthralgia/arthritis, and an evanescent rash. To our knowledge, we are reporting the first U.S. case presenting with the triad of dermatomyositis-like rash, proximal muscle weakness, and muscle atrophy without inflammatory myositis. Although AOSD and dermatomyositis are distinct clinical entities, both converge on the downstream JAK-STAT signaling pathway, a therapeutic target in refractory disease. A literature review suggests that dermatomyositis-like rashes represent an atypical AOSD variant more common in the Asia-Pacific region. Recognition of these rashes is essential, as they are linked to delayed diagnosis, refractory disease, and increased mortality.