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An African-American medical student presented with a new dark band on her index finger for 1 year (Figure 199-1). The dark color and the lack of melanonychia in other fingers made this concerning. A biopsy of the nail matrix was performed, and the result showed a benign nevus.
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Atypical pigmentation of the nail plate may result from many causes, such as melanin or hemosiderin within the nail plate, inflammatory changes, benign melanocytic hyperplasia, nevi, drugs, fungal infections, and endocrine disorders. It may also result from development of subungual melanoma. The challenge for the clinician is separating the malignant from the nonmalignant sources.
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Longitudinal melanonychia (LM or melanonychia striata) is a pigmented band in the nail plate resulting from melanin deposition (Figures 199-1 and 199-2). This may result from activation or proliferation of nail matrix melanocytes. It may involve 1 or several digits, vary in color from light brown to black, vary in width (most range from 2 to 4 mm), and have sharp or blurred borders.
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Benign LM is more common in more darkly pigmented persons. It occurs in 77% of African Americans older than age 20 years and in almost 100% of those older than age 50 years.1,2 It also occurs in 10% to 20% of persons of Japanese descent. LM is common in Hispanic and other dark-skinned groups. LM is unusual in whites, occurring in only approximately 1% of the population.1
Melanoma is the seventh most common cause of cancer in patients in the United States. Subungual melanoma is a relatively rare tumor with reported incidences between 0.7% and 3.5% of all melanoma cases in the general population.3
Subungual melanoma arises on the hand in 45% to 60% of cases, and most of those occur in the thumb (Figures 199-5, 199-6, 199-7).4 On the foot, subungual melanoma usually occurs in the great toe.5 The median age at which subungual melanoma is usually diagnosed is in the sixth and seventh decades. It appears with equal frequency in ...