Pigmented eccrine poroma in an atypical location

Abstract

Eccrine poroma is the term that includes benign neoplasms of the terminal duct of the eccrine sweat glands, which may clinically and dermoscopically resemble other melanoma and non-melanoma skin tumors. They are often located on the extremities (especially palms and soles), presenting as normochromic or erythematous papules and nodules, measuring up to 2 cm. Pigmented variants are uncommon, accounting for less than 20% of cases. This report describes a 37-year-old man who developed a large pigmented eccrine poroma on his right shoulder, causing diagnostic difficulty. Histopathological examination revealed a nodular neoplasm consisting of small, monomorphic, cuboidal cells, with ample, eosinophilic cytoplasm and well-defined borders, in addition to conspicuous intercellular bridges, with melanin deposits diffusely distributed inside them. The absence of cytological atypia, cellular pleomorphism, increased mitotic activity, and necrosis foci corroborated the diagnostic exclusion of porocarcinoma, which can develop from eccrine poroma.