Acquired reactive perforating collagenosis, a rare entity at uncommon site

Acquired reactive perforating collagenosis (ARPC), rare disorder characterized by transepidermal elimination (TEE) of collagen fibers, is seen in adult diabetics. Genetic predisposition, familial aggregation, trauma, bites and scratching are implicated. Diabetics develop microvascular diseases leading to intense pruritus causing repeated micro trauma leading to necrosis of connective tissue of dermis, causing TEE. Isolated papules, plaques and nodules with central keratotic plugs, are mostly seen on extensor surfaces of limbs but trunk and face may be involved. Histopathology shows extrusion of abnormal collagen fibers through epidermis. Multiple treatment modalities show variable response. A 52 year old diabetic female had multiple, itchy, well defined, erythematous papules and plaques with central adherent crusting on lower back since 1 month. Histopathology showed cup shaped epidermal depression filled with plug of altered collagen, acanthotic epidermis with hyperkeratosis and parakeratosis. Underlying epidermis was thin with fine slits through which vertically oriented basophilic collagen fibers were extruded.