Severe Edematous Facial Myositis Following Dual Influenza and COVID-19 Vaccination: A Case Report.

Idiopathic inflammatory myopathies (IIM), or myositis, are a heterogeneous group of autoimmune disorders that can affect multiple organs, including the muscles, skin, joints, lungs, heart, and gastrointestinal tract. While new-onset myositis has been reported following SARS-CoV-2 infection, cases associated with COVID-19 vaccination remain rare. We describe a unique case of severe progressive edematous facial myositis resembling angioedema in a 22-year-old man, with onset one to two weeks after receiving dual SARS-CoV-2 and influenza vaccinations. This ultimately led to a diagnosis of systemic inflammatory myositis with extensive involvement of proximal muscles in the arms and legs. We outline the clinical course, diagnostic investigations, and treatments, and discuss the potential molecular mechanisms and existing literature on inflammatory myositis induced by SARS-CoV-2 infection or mRNA-based vaccination.