Anti-MDA5 Dermatomyositis with RP-ILD and CMV Reactivation: A Case Report

Anti-melanoma differentiation-associated gene 5 (anti-MDA5) dermatomyositis is a distinct subtype of dermatomyositis frequently associated with clinically amyopathic disease and rapidly progressive interstitial lung disease (RP-ILD), a complication characterized by high mortality despite aggressive treatment. Early recognition and prompt immunomodulatory therapy are therefore critical. We report a fatal case of anti-MDA5 dermatomyositis complicated by RP-ILD with concomitant cytomegalovirus (CMV) reactivation. A 40-year-old woman with known dermatomyositis presented with progressive dyspnea, fever, and hypoxemia. Physical examination revealed typical cutaneous findings, including Gottron's sign and papules. Laboratory evaluation demonstrated elevated inflammatory markers and marked lymphopenia. Anti-MDA5 antibody testing was positive. Chest computed tomography showed rapidly progressive bilateral fibrotic interstitial lung disease compared with imaging obtained 10 days earlier. Despite empirical antimicrobial therapy, mycophenolate discontinuation, and initiation of intravenous immunoglobulin, respiratory failure progressed rapidly, requiring mechanical ventilation. Infectious investigations were negative except for low-level CMV viremia. Due to the absence of lung-specific diagnostic evidence, CMV was interpreted as reactivation related to immunosuppression rather than a primary cause of pulmonary injury. The patient subsequently developed multiorgan failure and died on the fifth day of intensive care. This case highlights the fulminant course and poor prognosis of anti-MDA5-associated RP-ILD. Severe lymphopenia and CMV reactivation may represent markers of immune dysregulation rather than direct etiologic drivers. Anti-MDA5 positivity should be recognized as a high-risk biomarker warranting early risk stratification, rapid initiation of immunomodulatory therapy, and close monitoring for opportunistic infections.