Pigmented Lesions of the Nail Unit: Clinical and Histopathologic Features

Probably the most common reason to perform biopsy of the nail unit is for the evaluation of
irregular pigmentation, especially longitudinal melanonychia or pigmented bands. When narrow
and solitary, these are usually the product of melanocytic activation/hypermelanosis,
lentigines, or melanocytic nevi. Multiple pigmented bands are generally a benign finding, the
result of melanocytic activation, as seen in racial pigmentation in darker-skinned patients, for
example. In the context of an irregular, broad, heterogeneous or “streaky” band, the chief
concern is the exclusion of subungual melanoma. Before assessing the histologic features of
any such entities, it is important to understand the normal nail anatomy and melanocytic density
of nail unit epithelium, as well as the type of specimen submitted, and whether it is adequate to
undertake a proper histologic evaluation. The criteria for diagnosis and prognosis of melanoma of
the nail unit are still evolving, and a variety of factors must be weighed in the balance to make a
correct diagnosis. The importance of the clinical context cannot be overemphasized. There are also
nonmelanocytic conditions to be considered that may produce worrisome nail discoloration, such
as subungual hemorrhage, squamous cell carcinoma, and pigmented onychomycosis.
Semin Cutan Med Surg 29:148-158 © 2010 Elsevier Inc. All rights reserved.

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