Anti- melanoma differentiation-associated gene 5 antibody-positive dermatomyositis with rapidly progressing interstitial lung disease

Background Anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibody-positive dermatomyositis is a rare subset of idiopathic inflammatory myopathy with a distinctive skin phenotype, little or no muscle involvement and a high risk of rapidly progressive interstitial lung disease (RP-ILD). Normal muscle strength and creatine kinase often lead to misdiagnosis as infection or idiopathic ILD. We report this case because the skin findings were the only clue to a fulminant lung process, and because the adequacy of sequential step-up immunosuppression in high-risk disease remains unresolved. Case presentation: A 60-year-old never-smoking man presented with 3 months of progressive dyspnea, dry cough, fever, 10-kg weight loss and a photosensitive rash. He was hypoxemic (SpO2 88% on room air) with bibasal crackles, heliotrope rash, shawl sign, Gottron papules, ulcerated chest papules and mechanic's hands. Muscle power and creatine kinase were normal. C-reactive protein, D-dimer and lactate dehydrogenase were elevated; ferritin was 450 ng/mL. Computed Tomography (CT) Pulmonary Angiography showed basal-predominant ground-glass opacities with subpleural sparing and traction bronchiectasis, without thromboembolism. Extensive infectious work-up, including bronchoalveolar lavage, was negative. Antinuclear antibody was positive (1:320) and the myositis-specific antibody panel was strongly positive for anti-MDA5. He received pulse methylprednisolone, tapering oral glucocorticoids and intravenous immunoglobulin, but deteriorated rapidly, requiring non-invasive ventilation, intubation and tracheostomy; repeat CT chest showed dense consolidation. Ventilator-associated pneumonia and refractory septic shock followed, and he died on hospital day 18. Conclusions Myositis-specific antibodies should be tested promptly in any patient with subacute hypoxemic ILD and compatible skin findings, even when muscle strength and creatine kinase are normal, and the infectious work-up should run in parallel with treatment. Glucocorticoids with immunoglobulin alone were inadequate; early combination immunosuppression and multidisciplinary care, weighed against opportunistic infection risk, should be considered in high-risk patients.