Endocardial fibroelastosis: myocardial and vascular alterations associated with viral-like nuclear particles.

Although clinical, immunologic, and experimental evidence exists implicating in utero viral infection of the myocardium in the development of primary endocardial fibroelastosis, the infectious etiology of this condition remains somewhat controversial. To date, specific features of viral myocarditis and morphological demonstration of viral particles have not been described in EFE. The present case is the first in which extensive light microscopic and ultrastructural analysis of the myocardium revealed abnormalities consistent with a primary viral myocarditis associated with typical EFE. These alterations consisted of chronic myocardial inflammation, extensive interstitial fibrosis, severe degenerative changes in myocardial cells, and a marked proliferation of endothelial cells in large nad small intramyocardial vessels leading to vascular occlusions. In support of the infectious etiology of this disease, similar features were noted in skeletal muscle. Most interestingly, viral-like particles were observed in many myocardial and endothelial nuclei. Although we are not absolutely certain of the viral nature of these particles, their appearance suggests viral assoicated material. We propose that the presence of these particles in this case in association with the other morphological alterations in support for the viral etiology of EFE. The prominent vascular occlusion observed in the myocardium may be an important clue to the pathogenesis of fibroelastosis as either a primary or secondary disease.