Electron microscopic study of the colloid-like substance in solar elastosis.

We have made electron microscopic studies on the elastotic material of solar elastosis which developed in cutis rhomboidalis nuchae taken from 10 males, 50-83 years of age. It was revealed that this material of the cutis rhomboidalis nuchae contained a colloid-like substance consisting of both a fine granular and an amorphous component. The colloid-like substance closely resembled that which is seen in the adult-type colloid milium, and could not be distinguished from it under light microscopy. In view of the morphological similarity at the ultrastructural level between the elastotic material and the colloid-like substance, it was proposed that normal elastic fibers can change into elastotic material and then further degenerate into the colloid-like substance, eventually becoming the typical colloid substance seen in colloid milium.