B43-16 Anti-MDA5 Antibody-Positive Dermatomyositis With Rapidly Progressive Interstitial Lung Disease: A Case Report

Abstract Introduction Anti-Melanoma Differentiation-Associated Gene 5 (MDA-5) antibody-positive dermatomyositis (MDA5-DM) is a distinct subtype of idiopathic inflammatory myopathy characterized by high mortality due to rapidly progressive interstitial lung disease (RP-ILD). This case illustrates the diagnostic challenges and therapeutic dilemmas in managing refractory MDA5-DM in an elderly patient. Case Description A 75-year-old female presented with cough, fever, and dyspnea. Physical examination revealed tachypnea (38 breaths/min) and hypoxemia (SpO2 88-90% on 3L/min O2). Laboratory studies showed elevated inflammatory markers (CRP 43.2 mg/L, ESR 101 mm/h) and muscle enzymes (CK 370 U/L, LDH 402 U/L). Arterial blood gas analysis demonstrated type I respiratory failure (PaO2/FiO2 175.7). Chest computed tomography (CT) revealed bilateral ground-glass opacities with lower lung predominance. Anti-MDA5 antibodies were confirmed with a titer of 1:100. Despite initial management with meropenem and high-flow nasal oxygen, she developed progressive hypoxemia requiring intubation on day 4. Transfer to the Emergency Intensive Care Unit (EICU) prompted veno-venous extracorporeal membrane oxygenation (V-V ECMO) initiation. Autoimmune serology confirmed the MDA5-DM diagnosis, leading to treatment with methylprednisolone 500 mg daily, plasma exchange, and high-dose intravenous immunoglobulin (IVIG) pulse therapy. The subsequent course was complicated by polymicrobial infections (A. baumannii, S. haemolyticus, fungi) and coagulopathy. Despite broad-spectrum antimicrobials and intensified immunosuppression with mycophenolate mofetil and upadacitinib, she developed pneumothorax on day 18 and ultimately succumbed to respiratory-circulatory collapse on day 24. Discussion This case exemplifies three critical aspects of MDA5-DM management: First, the diagnostic challenge of distinguishing RP-ILD from infectious pneumonitis, particularly with non-specific initial presentation; Second, the precarious balance between aggressive immunosuppression and infection risk—our patient developed lethal opportunistic infections despite microbiological control; Third, the limited efficacy of conventional and rescue therapies (including V-V ECMO and plasma exchange) in end-stage disease. The rapid progression from diagnosis to mortality (24 days) despite multimodal therapy underscores the therapeutic recalcitrance in elderly MDA5-DM patients. This highlights the need for earlier detection strategies and novel treatment approaches for this devastating disease. This abstract is funded by: None