Longitudinal melanonychia: Diagnosis, biopsy and pathology

March 7, 2009

San Francisco - Differentiating melanonychia, selecting the appropriate biopsy when indicated and carefully handling specimens were topics of presentations Saturday at the 67th Annual Meeting of the American Academy of Dermatology here.

San Francisco

- Differentiating melanonychia, selecting the appropriate biopsy when indicated and carefully handling specimens were topics of presentations Saturday at the 67th Annual Meeting of the American Academy of Dermatology here.

Longitudinal melanonychia is the most important nail disorder, as it is the possible presentation of melanoma, said Nathaniel J. Jellinek, M.D., assistant professor, Warren Alpert Medical School, Brown University, Providence, R.I.

Nail melanoma can be obvious, but can hide in brown and even red bands, and can be amelanotic, Dr. Jellinek said.

The most common cause of melanonychia in adults is melanocytic activation, with no proliferation, Dr. Jellinek said. The most common cause in children is benign proliferation - a lentigo or nevus - while malignant proliferation (melanoma) is seen much more often in adults.

Melanonychia is much more prevalent in black patients, he said.

"The majority will have melanonychia by the time they’re an adult," and 15 percent to 20 percent of melanomas will be nail melanoma, Dr. Jellinek said.

"A true white skin type I person really has no reason having a dark band" in the nail, he said.

Dermoscopy can help guide biopsies, Dr. Jellinek said. Direct rather than polarized light dermoscopy is optimal for the nail plate, he said, and water-soluble gels are best for use on the plate.

When examining a nail, the findings of "a brown background and irregular lines are strongly associated with melanoma."

The doctor’s approach also must include a detailed history and complete skin and mucosal exams.

A key question with longitudinal melanonychia is, "Is it coming from melanocytes or not? If it is, you have to think more carefully about melanoma," he said.


Several different methods of biopsying the nail matrix are available, and the best-suited will depend on how the nail band presents, said Siobhan C. Collins, M.D., department of dermatology, University of Connecticut School of Medicine, Farmington, Conn.

"All bands are not created equal," she said.

Physicians must consider whether invasive melanoma is suspected, and should also consider the location of the band, the width of the band, and the origin of the band in the matrix.

In addition to the punch biopsy, Dr. Collins discussed the uses for several other methods, including the matrix shave biopsy, which she said is the most versatile procedure.

It is particularly suited to the proximal matrix, she said, and minimizes scarring.

However, "If you do suspect invasive melanoma, it’s not the procedure you would choose."

The midline paramedian biopsy Is "excellent for centrally located bands that are on the thinner side," she said.

The lateral longitudinal biopsy is well-suited for laterally located bands and is "good for ambiguous nail presentations," Dr. Collins said.

Dr. Collins said she doesn’t often use the transverse matrix biopsy. "It’s OK when you suspect invasive melanoma, but remember that longitudinal melanonychia is longitudinal," she said.

The en bloc excision method is the first-line treatment for melanoma in situ, she said.


Beth Ruben, M.D., associate professor, departments of dermatology and pathology, University of California, San Francisco, discussed the histologic aspects of melanonychia.

"We are often faced with a lack of clinical information when we receive these specimens," she said.

Among the challenges pathologists face are varying thicknesses of biopsy specimens, variable handling of specimens, and the fact that most biopsies are partial biopsies.

On a requisition form, she noted, "The width of the band or streak is really the most important thing I’d like to know."

Careful handling of specimens also is "so important, both intraoperatively and post-operatively," she said. "Do a really great biopsy, and you’re most of the way there." DT