Eruptive vellus hair cysts (occlusion and cystic dilatation of vellus hair follicles) commonly present as asymptomatic small red, yellow, bluish-grey or brown, papules (occasionally scaly) on the chest, abdomen (A), and axillae (B) in the second decade of life. They were first reported in 1977. The diagnosis is often made clinically, because of typical age of onset (before puberty), the site of the lesions, and their appearance. Histopathologic examination reveals a cystic structure located in the middle or upper dermis. It is lined by a stratified squamous epithelium with focal features of outer root sheath differentiation at the level of the follicular isthmus and trichilemmal cornification. The lumen contains keratin and numerous transversely and obliquely sectioned vellus hair shafts. Some cysts may show a connecting pore at the skin surface, the likely mechanism of the spontaneous regression. Also, incision or puncture of the cyst and examination of the contents in potassium hydroxide, under a microscope will reveal the vellus hairs. Eruptive vellus hair cysts can overlap clinically and pathologically with steatocystoma multiplex (hybrid cysts). The so-called steatocystoma multiplex suppurativa mimics acne conglobata. Twenty-five percent of eruptive vellus hair cysts cases spontaneously regress through transepidermal elimination. Various methods have been used to treat the lesions but beware of scarring. The lesions may clear after application of topical retinoids. Erbium: YAG laser has been successful in treating the lesions*.
*Kageyama N, Tope WD. Treatment of multiple eruptive hair cysts with erbium : YAG laser. Dermatol Surg 1999; 25: 819–22.
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