The perforating disorders.

This article reviews the diseases that may show epidermal perforation as a histologic feature. Many of these represent examples of transepithelial elimination (TEE), a mechanism by which the skin rids itself of abnormal substances. After a review of disorders in which perforation is an occasional finding, four diseases that have been considered essential perforating disorders are discussed: elastosis perforans serpiginosa (EPS), reactive perforating collagenosis (RPC), perforating folliculitis (PF), and Kyrle 's disease (KD). A review of the literature, including recent reports of perforating diseases associated with chronic renal failure, suggests that there may be considerable clinical and histologic overlap among PF, KD, and the adult form of "perforating collagenosis." A working classification for the perforating disorders is suggested.