Abstract:

Poromas are relatively uncommon adnexal neoplasms that classically arise on acral surfaces of middle-aged adults, although occurrence on other anatomic sites can occur. Because poromas typically present as skin-colored to pink dome-shaped papules, the clinical differential diagnosis may include keratinocytic lesions such as seborrheic keratosis, verruca vulgaris, or basal cell carcinoma; however, rare cases of pigmented poromas, including one congenital case, have been reported, which may mimic melanocytic entities. Herein, we present a case of a 91-year-old white man with a large, pigmented lesion on the thigh. Three tangential biopsies were obtained from anterior, posterior, and lateral portions of the lesion, with an accompanying clinical history of rule out malignancy arising in a congenital nevus. Each specimen demonstrated an intraepidermal proliferation of monotonous cells with ductal differentiation and scattered pigment deposition. A SOX10 immunohistochemical stain was negative in the cells of interest, and Ki-67 demonstrated a low proliferative index with positivity primarily confined to the basilar layer. The diagnosis of pigmented intraepidermal poroma was rendered for each biopsy, allowing for conservative clinical management. The congenital nature of the lesion, along with the anatomic location and pigmented appearance, makes this case of intraepidermal poroma quite unusual. Furthermore, the importance of biopsy is highlighted, as misdiagnosis may lead to inappropriate clinical management.

Financial Disclosure:
No current or relevant financial relationships exist.

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Madison Hannay, DO