A large hyperpigmented patch with overlying darker macules and papules is characteristic of a speckled lentiginous nevus (SLN), also called a nevus spilus.
SLN is a cafe-au-lait˗like nevus that initially appears with a hyperpigmented background, usually at or around birth. Later, a speckled or polka-dot pattern of dark macules and papules appears over time. SLN is believed to be a form of congenital melanocytic nevus. There are believed to be 2 subtypes of SLN: nevus spilus maculosus and nevus spilus papulosus.
The maculosus subtype is characterized by flat and evenly distributed macules, that look like polka-dots. Histopathology reveals elongated interpapillary ridges containing increased numbers of melanocytes that form nests at the dermo-epidermal junction.
The papulosus subtype (which this patient had) is differentiated by superimposed speckles and papules whose size and distribution vary; this subype looks similar to a starry sky. Histopathology of the papulosus subtype shows melanocytic nevi of either the dermal or compound type—hence the papular appearance.
Given that SLN is a congenital melanocytic nevus, there is a small risk of transformation to malignant melanoma. The papulosus subtype is believed to have a more dynamic course with more lesions appearing over time. The maculosus subtype is considered to have a slightly higher risk of transformation into malignant melanoma compared to the papulosus subtype.
It is important to recognize that SLN is a distinct clinical entity, rather than a large irregular nevus. Mistaking it for a large suspicious nevus would require multiple biopsies of the most suspicious areas or excision of the entire lesion. Treatment for SLN includes serial surveillance with biopsy or excision of any suspicious areas that arise. In this case, the patient did not have any areas warranting biopsy, so the plan was to have him followed with annual clinical surveillance.
Photo and text courtesy of Erik Unruh, MD, MPH, and Daniel Stulberg, MD, FAAFP, Department of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque.