Melanonychia

Abstract

Melanonychia, or melanin-derived brown-to-black nail pigmentation, is a diagnostic challenge for clinicians. The most serious disease of the nail unit, melanoma, primarily presents with melanonychia. However, melanonychia most often occurs as a result of benign etiologies such as nail matrix melanocytic activation, nail matrix melanocytic hyperplasia, and nail invasion by melanin-producing pathogens. Regrettably, patients with nail apparatus melanoma are often initially misdiagnosed, and due to diagnostic delays of an average of 2 years, melanoma of the nail unit carries a poor prognosis. Having a thorough knowledge of the various causes of melanonychia and using a systematic approach when evaluating brown-to-black nail pigmentation may help prevent misdiagnosis and thereby improve prognosis.

Figure 1

Racial melanonychia.

Figure 2

Traumatic melanonychia following a fracture of the great toe.

Figure 3

Drug-related melanonychia secondary to hydroxyurea-induced melanocytic activation.

Figure 4

Nail apparatus lentigo in an adult.

Figure 5

Nail apparatus nevus in a child.

Figure 6

Nail apparatus melanoma in situ in a middle-aged Caucasian adult.

Figure 7

Hutchinson's sign in a nail apparatus melanoma in situ.

Figure 8

Pseudo-Hutchinson's sign in a nail apparatus nevus.

Figure 9

Dermoscopy of the nail apparatus melanoma in situ seen in Figure 7. Notice the brown coloration of the background and the presence of irregular longitudinal lines per color, spacing, thickness, and parallelism.