Colloid milium exhibited histochemical reactions similar to those of lichen amyloidosus. Colloid in this condition was composed of an amorphous material and filaments of various sizes, whose characteristics were distinctly different from the amyloid in lichen amyloidosus. There was evidence that some parts of the amorphous substance and thin filaments were derived from decomposition of preexisting collagen fibers, but the major portion was believed to have been produced by fibroblasts in the lesion. The fibroblasts in the lesion showed dilated cisternae of rough-surfaced endoplasmic reticulum, pinching off of peripheral cytoplasm, and extracellular formation of fine filaments in their vicinity, which indicated an active fibrillogenesis. Various forms of junctional devices and half-desmosome-like structures were commonly observed among these fibroblasts. Elastic fibers, normal or showing actinic elastosis, were few.
Ken Hashimoto, Fox Miller, Eugene S. Bereston. Colloid MiliumHistochemical and Electron Microscopic Studies. Arch Dermatol. 1972;105(5):684–694. doi:10.1001/archderm.1972.01620080014006