Ultrastructure of human melanosis coli with reference to its pathogenesis.

Colonic mucosal biopsies from patients with melanosis coli were examined by electron microscopy. They showed apoptosis of colonic surface epithelial cells and phagocytosis of resulting apoptotic bodies by intraepithelial macrophages. The latter migrated to the lamina propria where intracellular degradation of the apoptotic bodies resulted in formation of lipofuscin, characteristic of this condition. The results showed the pathogenesis of human melanosis coli was identical to that determined in an animal model of this disease.