A form of pigmented nevus showing intense melanocytic activity around the dermo-epidermal junction. Large numbers of spindle-shaped melanocytes proliferate downward toward the dermis and usually a large amount of pigment is present. It was first described in 1976 and the bulk of patients reported have been young females with the lesions presenting on the thighs. (From Rook et al., Textbook of Dermatology, 4th ed, 1992, p185).