Eruptive vellus hair cyst.

Abstract

Eruptive vellus hair cysts (EVHC), first described by Esterly et al. in 1977, present as asymptomatic aggregations of one to four discrete papules, each measuring up to 2 mm.1 These lesions are pigmented and range in color from red‐brown to grey‐black. They are found most commonly on the chest, though they also have been reported on the forearms, thighs, popliteal fossae, forehead, and eyelids.The etiology of EVHC is unknown but may represent an abnormality of the development of vellus hair follicles. This condition does not appear to show a predilection toward either sex, and an autosomal dominant pattern of inheritance has been postulated.2 Arising spontaneously, the lesions are usually found in the young‐to‐middle‐aged patient. Though EVHC have not been responsive to oral vitamin A therapy or keratolytic agents; the cyst may resolve spontaneously in some patients. One author3 suggests this may occur via transepithelial elimination, while another author4 postulates that their resolution is due to an intracutaneous foreign body reaction.Histologic examination reveals that the cysts are found in the middermis. They are lined by several layers of squamous epithelium and contain laminated keratinous material. Vellus hair shafts may be seen within the confines of the cyst at various planes of the section. There often is a rudimentary follicle associated with the wall of the cyst. Vellus hairs, best seen under polarized light, are characteristic of this condition. Unless the integrity of the cyst wall has been violated, there is no evidence of inflammation.