The term nevus spilus (NS), also known as speckled lentiginous nevus, was first used in the 19th century to describe lesions with background café au lait–like lentiginous melanocytic hyperplasia speckled with small, 1- to 3-mm, darker foci. The dark spots reflect lentigines; junctional, compound, and intradermal nevus cell nests; and more rarely Spitz and blue nevi. Both macular and papular subtypes have been described.1 This birthmark is quite common, occurring in 1.3% to 2.3% of the adult population worldwide.2 Hypertrichosis has been described in NS.3-9 Two subsequent cases of malignant melanoma in hairy NS suggested that lesions may be particularly prone to malignant degeneration.4,8 We report an additional case of hairy NS that was not associated with melanoma and consider whether dermatologists should warn their patients about this association.
A 26-year-old woman presented with a stable 7×8-cm, tan-brown, macular, pigmented birthmark studded with darker 1- to 2-mm, irregular, brown-black and blue, confettilike macules on the left proximal lateral thigh that had been present since birth (Figure 1). Dark terminal hairs were present, arising from both the darker and lighter pigmented areas but not the surrounding normal skin.
A 4-mm punch biopsy from one of the dark blue macules demonstrated uniform lentiginous melanocytic hyperplasia and nevus cell nests adjacent to the sweat glands extending into the mid dermis (Figure 2). No clinical evidence of malignant degeneration was present.
The risk for melanoma is increased in classic nonspeckled congenital nevi and the risk correlates with the size of the lesion and most probably the number of nevus cells in the lesion that increase the risk for a random mutation.8,10,11 It is likely that NS with or without hair presages a small increased risk for melanoma,6,9,12 which is not surprising because NS is a subtype of congenital melanocytic nevus (CMN), a condition that is present at birth and results from a proliferation of melanocytes.6 Nevus spilus, however, appears to have a notably lower risk for malignant degeneration than other classic CMN of the same size. The following support for this hypothesis is offered: First, CMN have nevus cells broadly filling the dermis that extend more deeply into the dermis than NS (Figure 2A).10 In our estimation, CMN have at least 100 times the number of nevus cells per square centimeter compared to NS. The potential for malignant degeneration of any one melanocyte is greater when more are present. Second, although some NS lesions evolve, classic CMN are universally more proliferative than NS.10,13 The involved skin in CMN thickens over time with increased numbers of melanocytes and marked overgrowth of adjacent tissue. Melanocytes in a proliferative phase may be more likely to undergo malignant degeneration.10