Sudden death related myocarditis: a study of 56 cases.

Fifty-six cases of sudden death from myocarditis were reviewed to characterize the range of histologic appearances of myocarditis. All autopsy cases of myocarditis over 13 years (1996-2008) in the Toronto Forensic Pathology Unit, Ontario Forensic Pathology Service, were studied. In each case, historical documentation and histological slides were reviewed. The severity of myocarditis was graded qualitatively and quantitatively (the inflammatory index). We established the inflammatory index in order to classify the severity of myocarditis, by counting the mean number of inflammatory foci per section of myocardium. Based on the inflammatory index, myocardial inflammation was classified into four grades. Based on this classification, 47% of the cases were classified as marked myocarditis having an inflammatory index over 5, with the number of foci per slide varying from 3 to more than 10, while 20% were classified as mild myocarditis with an inflammatory index between 1.1 and 1.9 with the number of foci per slide varying from 0 to 6. The diagnosis of mild myocarditis is dependent on adequate sampling. We believe that the use of this inflammatory index enhances the post-mortem diagnostic sensitivity of myocarditis, especially in its mild form and correlates with qualitative assessment of the histologic severity of myocarditis.