Epithelial sheath neuroma: evidence supporting a hyperplastic etiology and epidermal origin.

An epithelial sheath neuroma (ESN) is a rare benign process of unknown pathogenesis, which is characterized histologically by multiple enlarged peripheral nerve fibers ensheathed by mature squamous epithelium. The histologic features can elicit concern for carcinomatous perineural invasion. The process is limited to the superficial dermis and is surrounded by a loose myxoid stroma, lymphocytic infiltrate and sometimes prominent infundibular cysts. The etiology of this peculiar entity has been debated and theories include a benign neoplasm, a hamartoma or an unusual reactive hyperplasia. There are only seven prior cases reported of ESN in the literature. Our case presented here is the first report to show connection of the ESN to the overlying epidermis and reactive epidermal hyperplasia. This suggests that ESN is indeed an unusual form of benign reactive hyperplasia. In addition, the clinical setting in this case was of pruritus and scratching in a background of papular urticaria, supporting the previous notion that ESN is probably a response to an external stimulus such as rubbing.