A Case of an Anti-MDA5 Antibody Positive Patient with Amyopathic Dermatomyositis and Rapidly Progressive Interstitial Lung Disease

Summary: Idiopathic inflammatory myopathies are part of a group of heterogeneous diseases that may involve multiple organ systems with no effect on muscle tissue. They were historically described according to their clinical and histological findings as polymyositis, dermatomyositis, and inclusion body myositis. Today these are increasingly categorized according to a number of myositis-specific antibodies (MSAs) associated with distinct clinical syndromes. Autoantibody against the melanoma differentiation-associated protein 5, or anti-MDA5 antibody, is a recognized MSA associated with a distinct clinical syndrome, including interstitial lung disease (ILD) and skin findings of dermatomyositis, with no evidence of myositis, referred as clinically amyopathic dermatomyositis. We present a case of anti-MDA5 antibody clinically amyopathic dermatomyositis with rapidly progressive ILD, to highlight the importance of anti-MDA5 antibody-associated clinically amyopathic dermatomyositis and raise awareness for prompt diagnosis and treatment management of associated interstitial lung disease.