Anti-MDA5 Dermatomyositis Induced by COVID-19 Following Recombinant SARS-CoV-2 Vaccination: A Case Report.

Dermatomyositis (DM) is a form of idiopathic inflammatory myopathy characterized by skeletal, cardiac, and pharyngeal muscle inflammation alongside distinctive dermatological features. Anti-melanoma differentiation-associated gene 5 antibody-positive DM (anti-MDA5 DM), a rare and severe autoimmune condition, is frequently associated with rapidly progressive interstitial lung disease, which poses significant mortality risks. Viral infections and vaccinations are potential triggers of the disease. However, the initiation and progression of anti-MDA5 DM remain unclear. This study aimed to investigate its initiation. We report a unique case of a 48-year-old Japanese female who developed anti-MDA5 DM following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection despite prior administration of three coronavirus disease 2019 (COVID-19) vaccine doses, including a recombinant adjuvant vaccine. The patient presented with hallmark dermatological and systemic symptoms, confirmed through clinical, serological, and histopathological evaluations. Immunosuppressive therapy with corticosteroids, tacrolimus, and cyclophosphamide resulted in significant clinical improvement despite the initial progression of lung involvement. This case underscores a rare presentation of anti-MDA5 DM likely triggered by dysregulated type I interferon signaling following SARS-CoV-2 infection and vaccination. While most reported cases have focused on messenger ribonucleic acid (mRNA) vaccines, this case implicates recombinant adjuvant vaccines as a potential risk factor. These findings highlight the critical need for clinician awareness of atypical autoimmune syndromes in the post-infection and post-vaccination context; they could help develop strategies for improving the prevention and treatment of anti-MDA5 DM. Further research is warranted to elucidate the underlying immunopathological mechanisms and improve management strategies for such complex cases.