KERATIN IN CUTANEOUS AMYLOIDOSES

When Congo red stain was the only criterion, "amyloid" was considered to be a single substance. With the advent of electron microscopy, this idea was further strengthened because unfortunately the ultrastructure of all amyloids including those of the skin was found to be uniform. Clinical dermatologists knew that there were two types of skin amyloidoses; one manifesting itself in the skin as well as in various internal organs, the other being exclusively limited to the skin. The first group included amyloidoses associated with multiple myeloma (now termed AL amyloid), infections (now termed AA amyloid), and familial hereditary disease (of chemically variable composition). The second group consisted of truly cutaneous diseases such as lichen amyloidosus, macular amyloidosis, and cutaneous epithelioma-associated amyloidoses. Nodular amyloidosis was thought to be the link between these two groups because occasionally it can become systemic disease; it turned out to be a systemic disease of immunoglobulin light-chain production with a limited skin manifestation. Today we realize that this clinical division was more important than histologic and ultrastructural analyses of amyloid deposits: the second group of amyloidoses occur exclusively in the skin because the amyloid substances come from a special degeneration of keratinocytes of the epidermis and its derivatives. © 1990.