An urticated skin rash

Case presentation

On clinical examination, a 64-year-old man was noted to have a jet-black, 0.4 cm diameter lesion of unknown duration on his back (Figure 1). The surrounding skin showed marked sun damage. Dermoscopy revealed a dark lesion (Figure 2) that had a central homogeneous black colour and an irregular periphery associated with blunt projections (pseudopods) and filamentous streams of pigment (radial streaming). Excision biopsy showed uniform naevus cells in the dermis and irregular, darkly pigmented intraepidermal melanocytes with atypical nuclei (Figure 3). The intraepidermal melanocytes were confluent and present both as nests and single cells.