Hutchinson's sign: a reappraisal.

Hutchinson's sign, periungual extension of brown-black pigmentation from longitudinal melanonychia onto the proximal and lateral nailfolds, is an important indicator of subungual melanoma. However, experience has demonstrated that Hutchinson's sign, although valuable, is not an infallible predictor of melanoma. Periungual pigmentation is present in a variety of benign disorders and, therefore, may lead to overdiagnosis of subungual melanoma. Periungual hyperpigmentation occurs in at least one nonmelanoma skin cancer, Bowen's disease of the nail unit. Hyperigmentation of the nail bed and matrix may reflect through the "transparent" nailfolds simulating Hutchinson's sign. "Pseudo-Hutchinson's sign" is a phrase coined to encompass these three simulants of Hutchinson's sign. Each represents a misleading clue to the diagnosis of subungual melanoma. Total reliance on the (apparent) presence or absence of periungual pigmentation may lead to overdiagnosis or underdiagnosis of subungual melanoma. All relevant clinical and historical information, including the presence or absence of periungual pigmentation, must be carefully evaluated in a patient suspected of having subungual melanoma. Ultimately, the diagnosis of subungual melanoma is made histologically.