Eruptive Vellus Hair Cysts: Report of a New Case with Immunohistochemical Study and Literature Review

Eruptive vellus hair cysts (EVHC) were uncommon lesions with 222 cases reported in the literature. A new case involved a 15-year-old male with a 4-year history of small brown-gray papules on the trunk and extremities. Microscopically, the lesions were small epidermoid cysts containing vellus hairs. Immunohistochemical analysis showed expression of keratin 1/10, calretinin, and p63, but not epithelial membrane antigen, filaggrin, or androgen receptors. EVHC could be inherited or acquired and might be associated with other genodermatoses like sebocystomatosis. Potential causes included hamartomatous follicular growth or infundibular keratinization issues leading to follicle occlusion. Despite being benign, EVHC was difficult to treat.