Keratoacanthoma

For 2 months, an asymptomatic rash had been present on the upper arms of a 16-year-old boy of normal weight. The rash, as seen on the patient's right arm, consisted of abundant fine papules. He had no other lesions.

Keratosis pilaris is a relatively common hereditary disorder produced by hyperkeratinization with plugging of the infundibulum of the hair follicle. The outer upper arms and anterior and lateral thighs are predominately affected; the buttocks and trunk are less commonly involved. Usually, the rash is bilateral and asymptomatic; however, it may be pruritic and, if inflamed, may be painful. Associated conditions include ichthyosis, atopic dermatitis, hyperandrogenism, obesity, and type 1 diabetes mellitus.

Robert P. Blereau, MD, of Morgan City, La, writes that the diagnosis of keratosis pilaris is based on the clinical appearance of numerous papules on the typical sites of predilection. The differential diagnosis includes acne vulgaris, miliaria, drug-induced eruption, lichen spinulosus, pityriasis rubra pilaris, psoriasis, adverse effects of lithium therapy, and uremia.¹

Keratosis pilaris is frequently resistant to all treatments. Topical keratolytics, including lactic acid, urea (carbamide), glycolic acid, salicylic acid, and tretinoin, may be tried. Advise the patient that while there is no cure, the rash may be controlled. Scratching, tight-fitting clothes, and abrasive treatments can cause secondary staphylococcal infection. Aggravating environmental factors include cold dry air, hot baths, and wool clothing.

REFERENCE:1. Weedon D. Skin Pathology. 2nd ed. London: Churchill Livingstone; 2002:482-483