Antinuclear Antibody (ANA)‑Negative, Anti-melanoma Differentiation-Associated Gene 5 (MDA5)‑Positive Dermatomyositis Presenting as Rapidly Progressive Interstitial Lung Disease: A Case Report.

Dermatomyositis (DM) is a rare, autoimmune myopathy characterized by proximal muscle weakness and pathognomonic skin findings, including Gottron's papules and a heliotrope rash. Anti-melanoma differentiation-associated gene 5 (MDA5)-positive DM is a distinct subtype often associated with rapidly progressive interstitial lung disease (RP-ILD) and may lack the classic features of DM. We present the case of a 43-year-old woman who developed persistent hypoxic respiratory failure after multiple vascular surgeries requiring repeated postoperative blood transfusions. Her respiratory failure was initially attributed to transfusion-related acute lung injury with progression to acute respiratory distress syndrome. Despite appropriate treatment, her respiratory condition worsened. Infectious and autoimmune workups, including bronchoscopy and ANA testing, were unrevealing. Persistent diffuse bilateral ground-glass opacities and new fibrotic changes on imaging prompted an extended myositis panel, which revealed positive anti-MDA5 antibodies, establishing a diagnosis of RP-ILD secondary to MDA5 DM. She was treated with rituximab, mycophenolate, and IV immunoglobulin, with clinical improvement and was discharged on 4L of supplemental oxygen. This case underscores the importance of considering anti-MDA5-positive DM in unexplained, progressive respiratory failure, highlighting the importance of early recognition and multidisciplinary management.