Acquired Perforating Dermatosis

Perforating dermatoses are a heterogeneous group which is characterized by a papulonodular rash with transepidermal elimination of dermal components. Traditionally, four classical forms of primary perforating dermatosis have been described, where the transepidermal elimination mechanism represents the hallmark of the disease: Kyrle disease (KD), reactive perforating collagenosis (RPC), elastosis perforans serpiginosum (EPS), and perforating folliculitis (PF).[1] Elastosis perforans serpiginosum begins in childhood and characteristically presents with the elimination of elastic fibers. Reactive perforating collagenosis also occurs during childhood with the expulsion of collagen fibers. In perforating folliculitis, it is the content of the follicle, with or without collagen or elastic fibers, that gets eliminated. Finally, Kyrle disease presents with transepidermal elimination of abnormal keratin.[2] However, there is some controversy in the literature considering the classification of KD. While a few authors consider KD being an acquired form of perforating dermatosis, some define it as a variant of prurigo nodularis which represents the end-stage of excoriated folliculitis.[3] The secondary form of this condition is known as acquired perforating dermatosis (APD). The term was proposed by Rapini in 1989 to designate all the perforating dermatoses affecting adults with diabetes mellitus (DM), chronic renal failure (CRF) and rarely, other systemic diseases, regardless of the eliminated dermal material.[3] Commonly, patients with APD present with umbilicated papules and plaques with predilection sites that include the trunk and extremities.[4] Although the pathogenesis of APD remains unclarified, some authors suggested that trauma and microvasculopathy may be the triggers of transepidermal elimination and degeneration of the collagen fibers.[5]