Agminated intradermal Spitz nevi arising on an unusual speckled lentiginous nevus with localized lentiginosis: a continuum?

We report an 18-year-old boy with a congenital pigmented lesion measuring 2 x 6 cm on his right thigh. About a third of the lesion was composed of numerous lentiginous macules superimposed on histologically normal and clinically nontan skin; in the remainder of the lesion, several macules and papules with histologic features of junctional and compound nevi were superimposed on clinically normal skin, which had a lentiginous pattern histologically. Some years later, eruptive intradermal Spitz nevi developed at one corner of the lesion. The combined clinical and histological features of the lesion fulfill descriptions for both segmental lentiginosis and an unusual variant of speckled lentiginous nevus. Our case points out the limitations of using strict diagnostic criteria to define speckled lentiginous nevus and offers an opportunity to consider the natural history of the lesion as a continuum from lentigines to melanocytic nevi. Moreover, the presence of eruptive intradermal Spitz nevi arising within the area of speckled lentiginous nevus lacking a distinct tan background, suggests the possibility that the entire area of the lesion per se constitutes an environment where development of nevi is enhanced.