Sudden death of a 12-year-old boy with severe myocardial fibrosis due to inapparent chronic myocarditis.

Sudden death due to unknown cardiac disease in children is an unusual occurrence. An apparently healthy 12-year-old boy without any physical restrictions collapsed suddenly and died despite cardiopulmonary resuscitation. The main autopsy finding was extensive scarring of the myocardium, especially the interventricular septum. This extensive scarring was exceptional for the young age. Histologically, replacement-type fibrosis with patchy lymphomonocytic infiltrate and infiltration by macrophages were observed. The case was diagnosed as chronic myocarditis, which may have progressed to dilated cardiomyopathy with inflammation or inflammatory cardiomyopathy.