Electron microscopic studies on Civatte body in Riehl's melanosis.

So-called Civatte bodies were investigated with light and electron microscopes in six patients with Riehl's melanosis. They were present in the lower part of the epidermis and/or in the upper dermis of the lesions of all patients. In the epidermis they were composed of wavily arranged fine filaments and entangled melanosomes, desmosomes and other cell organelles. In the dermis Civatte bodies seemed to transform into net-like or more amorphous masses. Melanosomes, desmosomes and other cell organelles were also observed within them, athough in small numbers. Dermal components containing collagen fibrils were occasionally seen to have merged into the rims of Civatte bodies in the dermis. And these Civatte bodies appeared to incorporate the adjacent dermal components and further mix with them to transform into amyloid-like filament masses. The amyloid-like filament masses consisted of straight and nonbranching filaments and were observed in the lesions of four patients under the electron microscope. However, they could not be identified as amyloid itself with light microscope, because they were negative in both the thioflavin T and congo red stainings.