ORIGINAL ARTICLE Sudden death related myocarditis: a study of 56 cases Indira D. Kitulwatte • Patrick J. H. Kim • Michael S. Pollanen Accepted: 23 October 2009 / Published online: 29 November 2009 Ó Humana Press 2009 Abstract Fifty-six cases of sudden death from myocar- ditis were reviewed to characterize the range of histologic appearances of myocarditis. All autopsy cases of myocar- ditis over 13 years (1996–2008) in the Toronto Forensic Pathology Unit, Ontario Forensic Pathology Service, were studied. In each case, historical documentation and histo- logical slides were reviewed. The severity of myocarditis was graded qualitatively and quantitatively (the inflam- matory 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. Keywords Sudden death Á Myocarditis Á Histopathology Á Inflammatory index Á Forensic pathology Introduction Myocarditis is defined as inflammation of the heart muscle that is frequently accompanied by myocellular necrosis. In the beginning of the nineteenth century, all the diseases of heart muscle not associated with valvular abnormalities were described as myocarditis [1]. Later at the beginning of the twentieth century, coronary artery occlusion was rec- ognized as a specific cause of heart muscle disease and the term myocarditis was of no use because it was too general. However, in the second half of the twentieth century, inflammation of the heart muscle, now termed as myo- carditis, was found in a number of postmortem studies [2–4] as well as in endomyocardial biopsy samples [5]. Due to high inter-observer and sampling variability, con- troversies existed over the diagnosis of myocarditis [6]. Myocarditis can be from various aetiologies, both infectious and non-infectious. Infectious agents include viruses, helminths, or bacteria [7]. Hypersensitivity myo- carditis may follow the administration of drugs or exposure to chemicals like hydrocarbons and physical agents like radiation. Sometimes myocarditis can be associated with systemic inflammatory diseases like sarcoidosis. Myocar- ditis is known to cause sudden cardiac death following a previous uneventful course. Publication of the Dallas criteria in 1987, established the histopathological diagnosis of myocarditis in endomyo- cardial biopsy specimens based on the presence of an inflammatory infiltrate and associated myocyte necrosis or damage not characteristic of an ischemic event [8]. How- ever, post-mortem studies showed that active myocarditis may result in only small focal areas of myocardial necrosis and therefore the chances of a false negative result is high [9, 10]. Due to the limitations associated with the Dallas criteria, alternative pathological diagnostic criteria I. D. Kitulwatte Á P. J. H. Kim Á M. S. Pollanen Centre for Forensic Science and Medicine, University of Toronto, Toronto, ON, Canada I. D. Kitulwatte Á P. J. H. Kim Á M. S. Pollanen (&) Forensic Pathology Unit, Ontario Forensic Pathology Service, 26 Grenville Street, Toronto, ON M7A 2G9, Canada e-mail: michael.pollanen@ontario.ca Forensic Sci Med Pathol (2010) 6:13–19 DOI 10.1007/s12024-009-9125-5