Histopathological characteristics of myocarditis following COVID-19 vaccination: a scoping review

Introduction: Cases of myocarditis in people who were vaccinated against COVID-19 have been reported in the recent years. Nevertheless, the histopathological features and the pathomechanisms in these cases are still unclear. Hence, a scoping review of existing literature was performed to discover the histopathological features of myocarditis induced by the above-mentioned vaccine. Material and Methods: A search was performed in the PubMed, Scopus and EMBASE databases to retrieve the relevant records, involving analyses of biopsy and autopsy specimens. Baseline characteristics of the patients and the histopathological characteristics of the respective specimens were extracted and recorded. Results: Overall, 24 case reports and case series (involving a total of 54 patients) were included in this scoping review. The following signs of inflammation were present in the specimens: lymphocyte infiltration (64.8%), eosinophilic infiltration (29.6%), neutrophil infiltration (3.7%) and giant-cell formation (1.9%). Other features included myocardial tissue necrosis (20.4%), the presence of the SARS-CoV-2 spike protein (16.7%) and microthrombosis (3.7%). Conclusions: The histopathological characteristics of SARS-CoV-2 vaccine-induced myocarditis were heterogenous, the only common characteristic was the presence of lymphocyte infiltration in more than half of the cases. Studies of unreported past cases may provide further insights into the topic.