Pathological findings of clinically suspected myocarditis temporally associated with COVID-19 vaccination

Reports on the pathological findings of patients with myocarditis after coronavirus disease 2019 (COVID-19) vaccination are limited. We present a case series of four patients with clinically suspected myocarditis temporally associated with COVID-19 vaccination who underwent endomyocardial biopsy with no evidence of viral genomes in tissue specimens. Two patients had fulminant myocarditis with marked inflammatory cell infiltration comprised mostly of CD8+ T-cells and macrophages, and the other two had suspected myocarditis based on the biochemical evidence of myocardial injury and ST changes on an electrocardiogram. However, they did not meet the histological criteria of myocarditis. Immunosuppressive therapy effectively reduced myocardial damage, and all four patients had improved clinical courses. Temporal association does not prove causation, and it cannot be excluded that the two biopsy-proven cases reported are simply a random association of a naturally occurring virus-negative immune-mediated lymphocytic myocarditis occurring after vaccination.