Microscopic examination revealed epidermal invaginations filled with keratin in concentric lamellae. Follicular walls showed changes of epidermolytic hyperkeratosis, including hypergranulosis, vacuolar degeneration of the granular cells, and irregular keratohyalin bodies.
Nevus comedonicus was first described by Kofman1 in 1895. It has been suggested that NC is an uncommon type of adnexal hamartoma, with abnormal differentiation of the epithelial portion.2 The follicular structure that results is unable to form terminal hair or sebaceous glands and is capable of producing only soft keratin, which accumulates in the adnexal orifices.2 The NC syndrome is characterized by skeletal, ocular, and central nervous system defects.3
Two Dark Plaques on the Thigh—Diagnosis. Arch Dermatol. 2003;139(1):93-98. doi:10.1001/archderm.139.1.93-a