Ectopic acanthosis nigricans at a post-syndactyly surgical site: An unusual reactive epidermal phenomenon

Acanthosis nigricans (AN) typically manifests as hyperpigmented, velvety plaques at intertriginous sites and is associated with insulin resistance, endocrinopathies, or internal malignancies. Its occurrence in ectopic, grafted, or surgical sites is exceptionally rare. We report a case of a 20-year-old woman who presented with persistent hyperpigmented and hypertrichotic plaques over the interdigital web spaces of both hands. She had undergone syndactyly-release surgery in infancy with full-thickness medial thigh grafts. Dermoscopy revealed linear crista cutis with brown dots. Histopathology demonstrated hyperkeratosis, papillomatosis, and basal layer pigmentation, confirming ectopic AN. Metabolic parameters were normal.Ectopic AN likely represents a reactive epidermal phenomenon in grafted skin due to epidermal–dermal mismatch and altered growth factor signaling. Awareness of this rare entity is important to avoid unnecessary metabolic or malignancy work-ups.