Slowly Progressive Melanoma Differentiation-Associated Gene 5 (MDA-5) Interstitial Lung Disease Following COVID-19 Infections: A Pulmonary Puzzle.

Melanoma differentiation-associated gene 5 (MDA-5) autoimmunity has been increasingly recognized in association with interstitial lung disease (ILD), particularly in the context of viral infections. While MDA-5 ILD is typically rapidly progressive with high mortality, emerging evidence suggests that COVID-19 may induce a distinct, more indolent phenotype. We report two cases of MDA-5 ILD following COVID-19 infection with a slowly progressive course. In Case 1, an 87-year-old woman with a history of breast cancer, chronic obstructive pulmonary disease (COPD), and a prior COVID-19 infection developed progressive dyspnea. Imaging revealed new-onset ILD with subpleural reticulations and traction bronchiectasis. A myositis antibody panel was positive for MDA-5 autoantibodies. She was diagnosed with MDA-5 ILD and initiated on corticosteroids, later transitioned to mycophenolate. She has since remained clinically stable over the past two years. In Case 2, an 84-year-old man with a history of smoking and asbestos exposure developed severe dyspnea and hypoxia after a mild COVID-19 infection. CT imaging revealed diffuse ground-glass opacities and interlobular septal thickening. He was diagnosed with MDA-5 ILD and Group 1 and 3 pulmonary hypertension. He was treated with mycophenolate and pulmonary vasodilators, leading to symptom stabilization. These cases illustrate a possible post-COVID-19 endotype of MDA-5 ILD that follows a slower disease trajectory, distinct from the classical rapidly progressive phenotype. The association between viral infections and MDA-5 autoimmunity is supported by prior studies demonstrating viral-induced interferon signaling and MDA-5 gene activation. Given the indolent nature of disease progression in our patients, a tailored immunosuppressive approach was pursued, resulting in the stabilization of symptoms and pulmonary function.  These cases contribute to the growing recognition of post-COVID-19 MDA-5 ILD as a unique clinical entity. Further research is needed to elucidate the precise mechanisms underlying virus-induced autoimmunity and to guide treatment strategies for this emerging ILD subtype.