[Nevoid acanthosis nigricans or RAVEN (rounded and velvety epidermal nevus): three cases]

We report three cases of a peculiar rash with mixed clinical features of both epidermal nevus and acanthosis nigricans. Their characteristics have been compared to those of very rare but similar cases found in the medical literature.

Two young adults (one male, one female) and a 7-year-old boy consulted for hyperchromic asymptomatic plaques located respectively on the right scapula, the left upper arm and the right frontotemporal area of the face. None had any noticeable familial medical history. None were overweight or had a personal history of diabetes or endocrine dysfunction. The plaques had appeared soon after puberty in the adults and at the age of 4 years in the child and they had remained stable for years. They were polycyclic in shape, sharply demarcated, and with a linear distribution. Their surface was slightly papular, with a velvety appearance and texture. No other skin or mucous membrane lesions were observed elsewhere. The physical examination was otherwise normal. Skin biopsy specimens showed mild acanthosis with papillomatosis, hyperorthokeratosis with elongated rete ridges and slight thinning of the roof of the dermal papilla.

The striking clinical features of this rash rule out confusion with any other epidermal nevus (because of age of onset, shape and texture) or with acanthosis nigricans (because of its topography and the lack of associated neoplastic or endocrine disease). A dozen similar case reports can be found in the medical literature, mostly under the term "nevoid acanthosis nigricans". Such a rash may be linked to postzygotic mosaicism with the same mutations of the FGFR3 gene. However, since the physiopathology of this rash remains hypothetical, we propose to name it "RAVEN", for "rounded and velvety epidermal nevus", which is simply a descriptive acronym and nothing more.