LAUSR

Amid the COVID-19 pandemic, the medical community has again observed how children may have different presentations and host immune responses to disease than adults. Fortunately, the prognosis has been overwhelmingly favorable for our youngest patients. Acute myocarditis, however, is a more complex scenario when examined across the age spectrum and the current study by Malek et al. yields further insights into the variable evolution of cardiac magnetic resonance imaging (MRI) findings over time in adolescent patients with myocarditis. Cardiac MRI is increasingly used to diagnose acute myocarditis and, in adults, commonly employed to differentiate myocarditis from acute coronary syndrome. In pediatric patients, however, the most relevant differential diagnosis is acute myocarditis vs. chronic dilated cardiomyopathy. While referral patterns for cardiac MRI likely vary between adult and pediatric centers, most experts believe that children generally present healthier than adults with acute myocarditis. Similar to findings from a multicenter retrospective study of cardiac MRI in pediatric patients, the subjects in Malek et al’s study had a low incidence of important ventricular dysfunction and heart failure. The strength of the current study is the prospective design in which all patients underwent a consistent cardiac MRI protocol and postprocessing technique, with a standard interval for follow-up surveillance exams. Unlike several previous pediatric studies, all enrolled patients met updated Lake Louise criteria using both T2and T1-based criteria. 3 Starting with a cohort of patients with universally MRI-confirmed disease, the authors systematically confirmed the recognized high incidence of persistent late gadolinium enhancement on follow-up cardiac MRI at a median of 7 months. The more compelling finding, however, was that they were able to categorize each patient in terms of active vs. resolved inflammation and found that nearly one-third of the patients had evidence of persistent edema at initial follow-up. These interesting findings and a few of the study’s limitations support the potential value of serial MRI surveillance in children who have had myocarditis and should drive further longitudinal study and continued methodologic development across patient age and size. While patients were enrolled prospectively and scanned systematically at 3T, the study captured only adolescents and highlights the frequent selection bias of many pediatric cardiac MRI studies. Younger children, who may have a worse prognosis in myocarditis, were not studied, likely due to anesthetic and other technical imaging considerations. The cardiac MRI community is keenly aware of the technical limitations of T2-weighted edema imaging and the pitfalls of its interpretation, especially in children. Unfortunately, quantitative mapping techniques were unavailable to the investigators at the time of the study and are challenging to adapt to smaller children with higher heart rates and limited normative data, although they are increasingly applied and improve diagnosis in pediatric myocarditis. Finally, while late gadolinium enhancement has emerged as a strong outcome predictor in adults with myocarditis, a low incidence and small sample sizes often preclude similar conclusions in children about outcome or risk stratification with respect to exercise or recovery. The old medical adage that “children are not simply little adults” remains true, if not prescient, in the current global context. Malek et al are applauded for their efforts to characterize myocarditis during adolescence. Our MRI community should continue to focus on closing the remaining clinical and technical knowledge gaps for our youngest and often most vulnerable patients.