Myocarditis in Sweden: A National Cohort Study 2009–2020

Background: Myocarditis is an inflammatory cardiac disease with a wide clinical spectrum of symptoms, extending from mild and often unrecognized cases to fulminant acute heart failure. The true incidence of myocarditis is unknown. It tends to affect the younger population and shows a male preponderance. When looking at the pediatric population, myocarditis presents a common cause of heart failure and cardiomyopathy, accounting for a significant portion of children undergoing heart transplantation. Since 2009, there exists a population-based national registry for pediatric heart disease (SWEDCON), covering >95% of Sweden’s pediatric population (0–18 years). Cases are registered by the responsible pediatric cardiologist. The aim of the current study was to gain insight into the epidemiology with respect to total cases, gender and age distribution, which diagnostic measurements were undertaken and fatal outcome of pediatric myocarditis in the Swedish cohort.

Methods: The SWEDCON-registry was used to identify the diagnosis of pediatric myocarditis during the years 2009–2020 in a national cohort. Medical records were used to collect medical details. The study was approved by the Swedish Ethical Review Authority.

Results: A total of 306 cases were registered, corresponding to an average cumulative incidence of 1.16 cases/100,000 children per year during the period 2009–2020. There was a clear overrepresentation of male cases (237; 77.5%). Age at diagnosis had a bimodal distribution as 15% of cases occurred in children younger than 3 years, and 70% in children older than 13 years. The mean and median age at diagnosis were 13.0 and 15.7 years, respectively. Diagnostic heart catheterization and MRI were reported in 5 and 15 cases, respectively. Fatal outcome was reported in 4 cases (1.3%).

Conclusion: This is the first study reporting population-based incidences of myocarditis in children using a nationwide registry. It confirms a clear male predominance and bimodal age distribution. Interestingly, only a few cases were diagnosed using either a heart biopsy or MRI. Fatality rate was very low. A nationwide study allows not only to infer reliable epidemiological data, but also to follow trends over time. Full coverage cannot be expected, however, since mild cases might be missed as well as fatal cases never registered. Further data investigation will allow the detection of trends over time.

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Artikel online veröffentlicht:
13. Februar 2024