Beyond Melanoma: Hutchinson's Sign in Subungual Melanocytic Activation - A Case Report

Hutchinson's sign, defined as periungual pigmentation extending into the surrounding nail folds, is conventionally considered a hallmark of subungual melanoma. However, several benign nail disorders may present with Hutchinson's sign, creating a diagnostic challenge for clinicians.

We report the case of a 33-year-old Saudi man who developed a progressive brown-black longitudinal band on his left little fingernail accompanied by pigmentation extending into the eponychium. Dermoscopy revealed irregularly spaced parallel lines with brush-like extensions in the proximal nail fold. Given the clinical suspicion of nail melanoma, a tangential nail matrix biopsy was performed. Histopathology demonstrated increased basal melanin deposition with cytologically bland melanocytes, which is consistent with subungual melanocytic activation. The patient was followed for 6 months. The nail completely regrew with no dystrophy, and the band had recurred.

This case highlights that Hutchinson's sign is not pathognomonic for melanoma and can occur in benign entities such as subungual melanosis. Careful integration of clinical, dermoscopic, and histopathological findings is essential for accurate diagnosis, avoiding unnecessary aggressive interventions while ensuring patient safety.