Persistent Milia, Steatocystoma multiplex and Eruptive Vellus Hair Cysts: Variable Expression of Multiple Pilosebaceous Cysts within an Affected Family

Abstract

Background: Steatocystoma multiplex (SM) and eruptive vellus hair cysts (EVHC) are conditions characterized by numerous cutaneous cysts with a clinical resemblance, such as age of onset, location, appearance of the lesions and mode of inheritance, but with distinctive histologic features. Recently, some authors have proposed that the two conditions are variants of one entity originating in the pilosebaceous duct, while others suggest that SM and EVHC are two distinct entities, on the basis of the different expression of keratins. Milia are small round cysts, commonly involving the face. In 1994, Menni and Piccinno reported the first association, in a family, between persistent infantile milia in a 9-month-old girl and SM in the father. The authors hypothesized a relationship between these two conditions. Objective: We describe a family in which the mother showed cystic lesions and milia and her 4-year-old son and her 18-month-old daughter presented persistant infantile milia. Methods: In addition to the clinical and genetic documentation, a biopsy was performed in the son and two biopsies in the mother. Results: The histologic examination of one of the son’s milium-like papules showed in the superficial dermis a small cyst typical of a milium. In serial sections it was possible to see a connection with a vellus hair follicle by an epithelial pedicle. The histologic examination of one of the mother’s papules on the forehead showed a large round cystic structure with histologic features of EVHC. Close to the cyst wall, serial sections showed flattened sebaceous gland lobules. The histologic findings of the second biopsy taken from the chest showed the typical features of a steatocystoma. Conclusions: The relationship between milia, SM and EVHC is discussed; the three diseases should be considered as subtypes of multiple pilosebaceous cysts that may all present overlapping histologic features. The different level of the pilosebaceous duct where the cyst originates should explain the different clinical manifestations.