Clinical differences between Hutchinson's sign in subungual melanoma and pseudo-Hutchinson's sign in benign longitudinal melanonychia.

Abstract

Hutchinson's sign (HS) is a strong clinical indicator of subungual melanoma (SUM); however, it is often clinically confused with pseudo-HS. This study aimed to analyze the clinical differences between HS in SUM and pseudo-HS in benign longitudinal melanonychia (BLM). We retrospectively reviewed the medical records of patients diagnosed with SUM or BLM. The clinical characteristics and dermoscopic findings of HS in SUM and pseudo-HS in BLM were compared. A total of 123 patients with SUM and 290 patients with BLM were included. HS was observed in 102 cases (82.9%) of SUM, while pseudo-HS was present in 130 cases (44.8%) of BLM. HS was more frequently associated with periungual pigmentation extending beyond half of the nail width (80.5%), pigmentation wider than the LM itself (37.8%), and discontinuous pigmentation (52.4%). In contrast, pseudo-HS was characterized by a linear lateral border (98.4%), proximal fading of pigmentation (93.8%), and disappearance of pigmentation on dermoscopy (75.2%). This study was a retrospective review conducted at a single tertiary center. When evaluating patients with LM and periungual pigmentation, assessing the width, continuity, lateral border, proximal fading, and dermoscopic features of the pigmentation can aid in differentiating HS from pseudo-HS.