Conference Coverage

Five rules for evaluating melanonychia


 

EXPERT ANALYSIS FROM SDEF HAWAII DERMATOLOGY SEMINAR

Rule #4: Don’t wimp out when a biopsy is warranted

Many dermatologists hem and haw about doing a biopsy for a concerning lesion on the nail, when they wouldn’t hesitate to biopsy a similarly suspicious lesion on the face.

But it’s essential to biopsy the right area, he added. For longitudinal melanonychia, that’s the matrix. The nail plate is the wrong place; a biopsy obtained there will result in an inappropriate benign diagnosis.

Nathaniel Jellinek, MD

Melanonychia from matrix lentigo

“The starter set is to do a punch biopsy. This is your gateway drug to the world of nail surgery. Lots of dermatologists are intimidated by nail surgery, but if you can do any minor surgery, you can do a punch of the matrix. All it takes is a little practice. And if all you can do is punch biopsies, you’re good for your career. If you can do that, you’re golden. There are people who’ve just done punch biopsies for their whole career and they don’t miss melanomas,” he said.

Step one is to undermine the proximal nail fold using a pediatric elevator, which costs only about $30. “If you’re going to do a lot of nail surgery, they’re really helpful,” he said.

There’s no need at all to evulse the nail. Just make oblique incisions in the proximal nail fold in order to reflect it and look at the matrix. A 3-mm punch is standard, directed right over the origin of the pigment. Resist the temptation to force or squeeze the specimen in order to extract it. Instead, use really fine-tipped scissors to nibble at the base of the specimen, then gently pull it out, making an effort to keep the nail plate attached to the digit and avoid getting it stuck up in the punch.

Rule #5: Have dermatopathologists extensively experienced with nail pathology on your Rolodex

The histopathologic findings present in early subungual melanoma in situ are often too subtle for general dermatopathologists to appreciate, in Dr. Jellinek’s experience. He cited other investigators’ study of 18 cases of subungual melanoma in situ, all marked by longitudinal melanonychia. Only half showed the classic giveaway on the original nail matrix biopsy, consisting of a significantly increased number of atypical melanocytes with marked nuclear atypia. Blatant pagetoid spread was infrequent. However, all 18 cases displayed a novel, more subtle, and previously undescribed finding: haphazard and uneven distribution of atypical solitary melanocytes with variably sized and shaped hyperchromatic nuclei (J Cutan Pathol. 2016 Jan;43[1]:41-52).

Dr. Jellinek reported having no financial conflicts regarding his presentation. SDEF/Global Academy for Medical Education and this news organization are owned by the same parent company.

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