The clinical appearance of clonal nevi (inverted type A nevi)

Background The term "clonal nevus" is used to describe a variant of melanocytic nevus that histologically exhibits a localized proliferation of pigmented epithelioid dermal melanocytes within an otherwise ordinary nevus (Ball NJ, Golitz LE. Melanocytic nevi with focal atypical epithelioid cell components: a review of seventy-three cases. J Am Acad Dermatol 1994; 30: 724-729). Reports to date have focused on the histologic appearance of these lesions. Aim To characterize the clinical appearance of clonal nevi. Methods Clinical and histologic examinations were performed of a single clonal nevus from each of five patients (two men and three women; age range, 37-80 years). Results All nevi were round to oval in shape with smooth, well-defined borders. They were uniformly tan to light brown in color, except for a single blue-gray to blue-black focus of hyperpigmentation. The diameters of the nevi ranged from 2.5 to 10 mm. In individual nevi, the hyperpigmented focus was either centrally or eccentrically located and measured 1-2 mm in diameter. Histologically, these lesions showed banal melanocytes associated with a localized proliferation of melanocytes with abundant pigmented cytoplasm in the dermis, admixed with melanophages. Conclusions The appearance of clonal nevi - tan with a focus of blue-gray to blue-black pigmentation - allows one to recognize the lesion clinically.