Colloid milium: light and electron microscopic investigations

A case of colloid milium (‘juvenile type’) is presented. Histochemically the colloid material showed the well known similarity to amyloid where especially in the upper portions of the colloid immunoglobulin and complement depositions could be found. Fibrin was demonstrated predominantly in the periphery of individual colloid islands. Electron microscopically, colloid exhibited a fibrillary structure. On the surface of the islands as well as enclosed within the colloid material numerous desmosome‐like structures could be visualized and sometimes also nuclear remnants were present. In circumscribed areas a fibrillary transformation of keratinocytes was observed. On the basis of these findings it is concluded that colloid represents tonofilament‐like material and therefore is of epidermal origin.