Differences between genetic dilated cardiomyopathy and myocarditis in children presenting with severe cardiac dysfunction

Acute myocarditis is an inflammatory disease of the myocardium, and it can present as severe heart failure in children. Differential diagnosis with genetic cardiomyopathy can be difficult. The objective of this study is to identify patterns of clinical presentation and to assess invasive and non-invasive measures to differentiate patients with acute myocarditis from patients with dilated genetic cardiomyopathy. We performed a retrospective descriptive study of all paediatric patients (0–16 years old) that presented with new-onset heart failure with left ventricle ejection fraction < 35% in whom we performed an endomyocardial biopsy (EMB) during the period from April 2007 to December 2020. The patients were classified into two groups: Group 1 included 18 patients with myocarditis. Group 2 included 9 patients with genetic cardiomyopathy. Findings favouring a diagnosis of myocarditis included a fulminant or acute presentation (77.8% vs 33.3%, p = 0.01), higher degree of cardiac enzyme elevation (p = 0.011), lower left ventricular dimension z-score (2.2 vs 5.4, p = 0.03) increase of ventricular wall thickness (88.8% vs 33.3%, p = 0.03) and oedema in the EMB. Seven (77.8%) patients with genetic cardiomyopathy had inflammation in the endomyocardial biopsy fulfilling the diagnostic criteria of inflammatory cardiomyopathy. Conclusion: Differentiating patients with a myocarditis from those with genetic cardiomyopathy can be challenging, even performing an EMB. Some patients with genetic cardiomyopathy fulfil the diagnostic criteria of inflammatory cardiomyopathy. Using invasive and non-invasive measures may be useful to develop a predictive model to differentiate myocarditis from genetic cardiomyopathy. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00431-021-04175-z.