Occurrence and Features of Childhood Myocarditis: A Nationwide Study in Finland

Background-Epidemiology of myocarditis in childhood is largely unknown. Men are known to have a higher incidence of myocarditis than women in adults aged <50 years, but whether this is true by sex in pediatric age groups is unknown. We set out to study the occurrence and potential sex differences of myocarditis in a general pediatric population. Methods and Results-Data of all hospital admissions with myocarditis in Finland occurring in patients aged <= 15 years from 2004 to 2014 were collected from a mandatory nationwide registry. All patients with myocarditis as a primary, secondary, or tertiary cause of admission were included. Total and age- and sex-specific incidence rates were calculated using corresponding population data. There were 213 admissions with myocarditis in pediatric patients. Myocarditis was the primary cause of admission in 86%. The overall incidence rate of myocarditis was 1.95/100 000 person-years. Of all patients, 77% were boys, but sex differences in incidence rates were age- dependent. In children aged 0 to 5 years, there was no sex difference in the occurrence of myocarditis. Boys aged 6 to 10 years had a higher incidence rate compared with girls (72% boys; incidence rate ratio: 2.46; 95% confidence interval, 1.03-5.89; P=0.04). Sex difference further increased in children aged 11 to 15 years (80% boys; incidence rate ratio: 3.5; 95% confidence interval, 2.68-5.67; P<0.0001). Conclusions-Myocarditis leading to hospital admission is relatively uncommon in children, but occurrence of myocarditis increases with age. There is no sex difference in the risk of myocarditis during the first 6 years of life, but boys have a significantly higher risk at ages 6 to 15 years.