Acquired reactive perforating collagenosis. Report of six cases and review of the literature.

Reactive perforating collagenosis (RPC) is characterized by transepithelial elimination of altered collagen. Two types have been recognized: the childhood form and the adult form. Our purpose was to review the associated disorders, evaluate the possible causes, and set criteria for the diagnosis of the disease. The clinical and pathologic findings of six patients with the adult form of RPC are reviewed. The literature on this subject is compared with our findings. Pruritus was reported in all cases. Treatment of pruritus cleared the lesions in many patients. This is the first report of an association between RPC and hyperparathyroidism, hypothyroidism, liver disorders, and neurodermatitis. Various disorders can be associated with the adult form of RPC. Pruritus is the common factor among all types. Control of itching might be helpful for clearing the lesions. We propose the following diagnostic criteria for acquired RPC: (1) histopathologic findings of elimination of necrotic basophilic collagen tissue into a cup-shaped epidermal depression, (2) clinical presentation of umbilicated papules or nodules with a central adherent keratotic plug, and (3) onset of skin lesions after the age of 18 years.