The extreme variability of clinical manifestations and frequently insidious onset of symptoms makes the true incidence and prevalence of myocarditis difficult to determine. Autopsy studies reveal myocarditis in 1% to 9% of routine postmortem exams, and a prospective postmortem study of sudden cardiac death in young adults suggests myocarditis as the etiology in approximately 10% of cases.[19]Blankenhorn MA, Gall EA. Myocarditis and myocardosis; a clinicopathologic appraisal. Circulation. 1956 Feb;13(2):217-23.
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[20]Doolan A, Langlois N, Semsarian C. Causes of sudden cardiac death in young Australians. Med J Aust. 2004 Feb 2;180(3):110-2.
https://www.mja.com.au/journal/2004/180/3/causes-sudden-cardiac-death-young-australians
http://www.ncbi.nlm.nih.gov/pubmed/14748671?tool=bestpractice.com
[21]Zeppenfeld K, Tfelt-Hansen J, de Riva M, et al. 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J. 2022 Oct 21;43(40):3997-4126.
https://academic.oup.com/eurheartj/article/43/40/3997/6675633?login=false
http://www.ncbi.nlm.nih.gov/pubmed/36017572?tool=bestpractice.com
Additionally, a large prospective trial of patients with dilated cardiomyopathy revealed myocarditis as the etiology in 9% of patients.[22]Felker GM, Hu W, Hare JM, et al. The spectrum of dilated cardiomyopathy. The Johns Hopkins experience with 1,278 patients. Medicine (Baltimore). 1999 Jul;78(4):270-83.
http://www.ncbi.nlm.nih.gov/pubmed/10424207?tool=bestpractice.com
A Finnish study in children ages ≤15 years estimated the annual incidence of myocarditis to be approximately 2 cases per 100,000 children.[23]Arola A, Pikkarainen E, Sipilä JO, et al. Occurrence and features of childhood myocarditis: a nationwide study in Finland. J Am Heart Assoc. 2017 Nov 18;6(11):e005306.
https://www.doi.org/10.1161/JAHA.116.005306
http://www.ncbi.nlm.nih.gov/pubmed/29151030?tool=bestpractice.com
In a retrospective US study of 212 children, 46% of myocarditis cases were in those ages 13-18 years, with a median age of 13.1 years.[24]Butts RJ, Boyle GJ, Deshpande SR, et al. Characteristics of clinically diagnosed pediatric myocarditis in a contemporary multi-center cohort. Pediatr Cardiol. 2017 Aug;38(6):1175-82.
http://www.ncbi.nlm.nih.gov/pubmed/28536746?tool=bestpractice.com
A slightly greater number of cases were in males (58%) than in females (42%).[24]Butts RJ, Boyle GJ, Deshpande SR, et al. Characteristics of clinically diagnosed pediatric myocarditis in a contemporary multi-center cohort. Pediatr Cardiol. 2017 Aug;38(6):1175-82.
http://www.ncbi.nlm.nih.gov/pubmed/28536746?tool=bestpractice.com
Female sex and younger age appeared to correlate with a worse clinical presentation and prognosis.[24]Butts RJ, Boyle GJ, Deshpande SR, et al. Characteristics of clinically diagnosed pediatric myocarditis in a contemporary multi-center cohort. Pediatr Cardiol. 2017 Aug;38(6):1175-82.
http://www.ncbi.nlm.nih.gov/pubmed/28536746?tool=bestpractice.com