Cardiovascular magnetic resonance imaging and endomyocardial biopsy in giant cell myocarditis: a case report on diagnostic challenges and future perspectives.

Background: Giant cell myocarditis (GCM) is a rare but often fast-progressing cardiac disease with a high risk of poor outcome. Nonetheless, its differentiation from other diseases like cardiac sarcoidosis (CS) using cardiovascular magnetic resonance imaging (CMR) remains challenging. Case summary: A 27-year-old male patient presented to the emergency department with acute cardiac decompensation and severely reduced left ventricular ejection fraction. After exclusion of an ischaemic cause of heart failure, CMR was performed, showing signs of acute inflammation and late gadolinium enhancement patterns that were indistinguishable between GCM and CS. Despite the suspicion of sarcoidosis based on a lymph node biopsy, endomyocardial biopsy (EMB) provided clear evidence of typical histopathological changes consistent with GCM. An immunosuppressive therapy was initiated leading to an improvement in left ventricular function. Discussion: Cardiovascular magnetic resonance imaging is an important cornerstone in the diagnostic pathway of GCM, however, only complementary use with EMB allows reliable diagnosis. Therefore, full diagnostic and especially prognostic potential of CMR remains unclear but offers an important starting point for optimizing patient management.