Whitish halo on a papular pigmented lesion

A 49-year-old healthy Caucasian woman presented with a sudden change in a lesion on her abdomen. At the time of our consultation, we observed a pigmented papular lesion, 1.5 cm in diameter, surrounded by an incomplete whitish halo with two dark rounded blotches at its top (Figure 1a). The patient had a fair skin phototype and chronic photoaging, characterized by atrophic skin, wrinkling, and diffuse solar elastosis, especially on the sun-exposed areas. Dermoscopy showed a brownish irregularly oval plaque with a few dotted vessels and regular globules. On top of the lesion, two heavily asymmetric and pigmented blotches were visible: on the left, it was bluish and on the right side reddish (Figure 1b). Histopathological examination revealed a compound, predominantly intradermal melanocytic nevus with congenital features adjacent to a focal scar, suggestive of a previous trauma or surgical procedure (Figure 2a). Within the lesion, an expanding dermal nodule was detected, characterized by nests of epithelioid melanocytes. No nuclear cell atypia, pleomorphism, mitosis, or pagetoid spread into the epidermis was observed (Figure 2b). The nodule was characterized by large melanocytes with minimal pleomorphism, without evidence of necrosis (Figure 2c). The periphery of the nodule showed maturation of the melanocytes blending with the surrounding nevus. Cells of the congenital nevus and cells of the dermal nodule were positive for S-100 protein and negative for HMB45. The Ki-67 proliferation index was low in the congenital nevus but moderately high in the nodule, while p-16 was negative in the nodule, but positive in the remainder of the nevus. BAP-1 immunohistochemistry revealed BAP-1 nuclear staining (Figure 2d).