Anti-MDA5 Antibody-Positive Dermatomyositis in Emirati Patients: A Case Series Highlighting Clinical Variability

BACKGROUND Melanoma differentiation-associated gene 5 (MDA5) is an intracellular sensor that detects double-stranded RNA viruses and triggers type I interferon pathways. Anti-MDA5 dermatomyositis (MDA5-DM) is an uncommon autoimmune subtype, often linked to rapidly progressive interstitial lung disease (RP-ILD) and sometimes presenting without obvious muscle weakness. It can appear in pulmonary, cutaneous-articular, or vascular forms, with RP-ILD carrying the worst prognosis. We describe 3 Emirati patients with MDA5-DM, each with a different clinical picture, organ involvement, and outcome. CASE REPORT Case 1: A 24-year-old man developed flu-like symptoms, rash, abnormal liver enzymes, and RP-ILD. His condition worsened despite high-dose steroids, cyclophosphamide, and plasma exchange; he required ECMO and died after 40 days. Case 2: A 62-year-old man with ILD presented with worsening dyspnea, weakness, and rash. He had high ferritin and lactate dehydrogenase levels, with positive anti-MDA5. He was treated with steroids, rituximab, nintedanib, and mycophenolate. High-resolution computerized tomography scans remained stable, but he required long-term oxygen after having pneumonia. Case 3: A 13-year-old boy had weight loss, stiffness, rash, and positive anti-MDA5. Magnetic resonance imaging confirmed myositis. He improved after steroids and intravenous immunoglobulin, with recovery of strength, weight gain, and normal function after prolonged treatment. CONCLUSIONS MDA5-DM is a rare and clinically diverse entity that can range from indolent skin-limited disease to life-threatening RP-ILD. This case series highlights the full clinical spectrum, from pediatric onset to fulminant adult disease. Multidisciplinary care, awareness of atypical presentations, and continued research into disease mechanisms and therapeutics are essential to improving survival in MDA5-DM.