Electron microscopic changes in tropical endomyocardial fibrosis.

Electron microscopic examination of cardiac tissue from seven patients with tropical endomyocardial fibrosis showed the endocardium to be replaced by maturing granulation tissue containing haphazardly arranged collagen bundles, smooth muscle cells, blood vessels and degranulated mast cells. Mature collagen was present on the luminal aspect of the granulation tissue. Myofibres showed mitochondrial swelling, lamella bodies, focal myocytoplasmic clearing and collapsed intercalated discs. Small calibre blood vessels exhibited endothelial swelling, areas of basement membrane duplication and collections of neutrophilic and eosinophilic leucocytes. Eosinophils showed alteration in granule morphology. These changes are similar to the lesions reported in endomyocardial disease with eosinophilia.