Uncommon Presentation of a Pseudo-Mamma on the Forearm

A 53-year-old woman with no relevant medical history was evaluated for a right forearm lesion that had remained asymptomatic for four years. Examination identified a firm, brown 6-mm nodule situated on top of a poorly demarcated, 2-cm brownish plaque with a mammillated surface. Dermoscopy displayed a central white cobblestone-like area bordered by a brown reticular network, findings that suggested either an adnexal tumor or a compound nevus. Ultrasound showed diffuse thickening of the soft tissues limited to the subcutaneous fat. Histologic analysis demonstrated basal hyperpigmentation and pilosebaceous units resembling Montgomery tubercles, without glandular components. Immunohistochemical staining (mammaglobin, GATA, CK7) confirmed eccrine differentiation. Altogether, these features supported the diagnosis of a pseudo-mamma.
Supernumerary nipples are relatively frequent but usually occur along the embryonic milk line. Ectopic locations represent about 5% of cases and may appear on unusual sites such as the back, limbs, face, or shoulders. A pseudo-mamma arising on the forearm, as observed here, is exceptionally uncommon. Dermoscopy can assist in distinguishing these lesions from other benign or malignant skin conditions, while histopathology remains crucial for a definitive diagnosis. This case expands the small number of published reports describing pseudo-mamma outside the milk line and highlights the importance of correlating clinical, dermoscopic, and histologic findings in atypical presentations.