Spectrum of Follicular and Sebaceous Differentiation Induced by Dermatofibroma

Background: The term "induction" has been used to designate epidermal changes above dermatofibroma. Whereas follicular differentiation has been reported frequently, sebaceous hyperplasia above dermatofibroma is considered a rarity. Objective: To characterize all changes overlying dermatofibroma and to determine their frequency Methods: Sections cut from 2 10 consecutive examples of dermatofibroma were stained with hematoxylin and eosin and analyzed for the presence or absence of induction, for the type of change induced, and for features associated with these findings. Results: The epidermis above dermatofibromas was acanthotic, simulating seborrheic keratosis in 62.9% of the cases, and areas of clear and pale cells similar to those of clear cell acanthoma were seen in 18.6%. Induction of adnexal differentiation was encountered in 41% of the cases. Follicular differentiation was seen in 10.9%, all of which showed some follicular germinative cells. In 9.5%, follicular germinative cells were present together with well-circumscribed mesenchymal papillae. In 4%, formation of a complete hair follicle was encountered. In 16.7% of the dermatofibromas, induction of sebaceous lobules was encountered, whereas sebaceous differentiation in the form of mantles was seen in 25.7% of the cases. Not uncommonly, sebaceous structures were arranged in a reticulate pattern similar to that seen in reticulated acanthoma with sebaceous differentiation (12%). Conclusions: Induction of adnexal structures is more common than currently perceived. Especially, induction of immature and mature sebaceous structures seems to be underrecognized.