A 51-year-old white man is seen for evaluation of a dark subungual stripe that appeared in his thumbnail six months ago. There are no symptoms to report and no history of trauma to the digit. His health is reportedly perfect otherwise.

When questioned, the patient admits to regular unprotected sun exposure. He chalks this up to the necessity of yard work, both at home and at his family’s lake cabin, where they spend several weekends and holidays each year. The patient’s father died of melanoma years ago.

On examination, a 3-mm-wide dark brown longitudinal stripe is seen on the affected fingernail, beginning in the distal lunular area and extending to the end of the nail plate. The margins of the stripe are quite even, as is the color. No such color changes are seen in the surrounding paronychial skin. The other fingernails and the toenails are free of changes.

The patient is quite fair, with blue eyes, reddish brown hair, and modest dermatoheliosis. However, no distinctly worrisome lesions are seen.

ANSWER

The correct answer is to biopsy the proximal origin of the lesion (choice “d”), because this lesion could represent a subungual melanoma, a potentially lethal cancer. In this patient’s case, with his personal sun damage and family history of melanoma, simple reassurance (choice “a”) would have been inappropriate. Submitting a portion of the distal nail plate to pathology (choice “b”) contributes nothing to the process of distinguishing benign from malignant. Seeing the patient every few months (choice “c”) ignores the present potentially dangerous situation, although it would at least keep the patient in the loop.

DISCUSSION

The so-called acral lentiginous (AL) melanomas (by definition, on feet or hands, under nails, in oral tissues, or in perianal, scalp, and genital areas) are especially dangerous by virtue of location. Detection and removal are often delayed as a result.

While ALs constitute only 7% of melanomas overall, they account for more than half of all melanomas in Asian and black people. These patients have a far worse prognosis with AL than would be expected.

Subungual melanonychia is usually benign, but is suspicious for AL melanoma under certain circumstances. Patients at risk include:

• Those in their fifth to seventh decade of life

• Those who have a pigment stripe larger than 3 mm

• Those who experience changes in the lesion.

Thumbnails are especially at risk compared, for example, to the index fingernail or toenail. Other factors include extension of pigment onto surrounding paronychial skin (Hutchinson sign) and positive personal or family history of melanoma. 

Our patient’s thumb lesion, his positive family history of melanoma, the width of his lesion, and his age all spoke to the need for biopsy. This can be done directly through the nail plate into the most proximal aspect of the lesion.

Alternatively, the cuticle can be surgically reflected proximally to facilitate removal of a portion of the proximal nail and subsequent biopsy or even removal of the lesion. Obviously, most patients with these lesions will need to be referred to dermatology for this procedure.

It is also important to note that by age 20, 77% of African-American patients will have developed at least one of these lesions. By age 50, virtually 100% of them will display the condition, often in the form of multiple lesions. These are almost always benign but bear watching for substantive change.

One should also be aware that 20% to 30% of all subungual melanomas are amelanotic—that is, they do not display dark pigment. Instead, they can be white, almost colorless, light tan, or even pink, so the key word is change.