Fulminant Myocarditis After mRNA COVID-19 Vaccine Evolving to Giant Cell Myocarditis

Pediatric inflammatory multisystem syndrome (PIMS-TS) is a rare entity observed in children with postinfectious hyperinflammatory syndrome. Cases have been reported, although rarely, after the mRNA SARS-CoV-2 (COVID-19) vaccine.

We present a case of a young man who developed PIMS-TS with fulminant myocarditis after a first dose of COVID-19 vaccination, with persistent evidence of inflammation despite multiple lines of therapy over the course of 2 years. He then experienced fulminant myocarditis that was resistant to anti-inflammatory therapies. Repeat endomyocardial biopsy was consistent with giant cell myocarditis.

Cases of giant cell myocarditis after COVID-19 vaccination have been reported in the past, however to our knowledge, none have been reported 2 years after a single dose and with intercurrent diagnosis of PIMS-TS myocarditis. This raises the question of a possible pathophysiologic association between the 2 diseases and immune dysregulation.

This case illustrates the importance of repeating the investigation and questioning the diagnosis when the progression of the disease is not typical.