Melanocytic causes of longitudinal melanonychia
The melanotic macule, sometimes called melanocytic activation, is the most common subtype of melanin-derived LM in adults, Dr. Lipner said. This benign condition results from increased melanin synthesis without an increase in the number of melanocytes, which will be evident on histopathologic examination of the nail bed. Any of a variety of triggers can provoke the increased pigment, which can range from endocrine disruptions to inflammatory conditions, such as psoriasis, to trauma (including nail biting or habit tics).
Pregnancy, normal ethnic variation, and chemotherapy administration are all also associated with melanotic macules. In any case, dermoscopy will show an LM characterized by a grayish background that contains darker grayish lines.
Melanocyte hyperplasia can also cause melanonychia, in which case the trick is sorting out which cases are benign and which are malignant, Dr. Lipner noted. And getting the diagnosis right in a timely fashion matters: “Ideally, we want to catch these melanomas in in situ stages where we can preserve the digit,” she said. “It’s been shown that there is no survival benefit for amputation versus en bloc excision for nail melanomas in situ.”
Nail matrix nevi are the most common cause of LM in children, Dr. Lipner said. Here, dermoscopy shows a brown background with brown lines, with regular color, thickness, and spacing.
On examination of a nail with a melanoma, “typically, we see features suggestive of melanoma but really no pathognomonic features,” she commented. Some signs that should prompt concern and a more thorough investigation, she said, include a dark brown or black band of LM; lack of homogeneity, such as the presence of lines of different colors; blurring of the borders of the pigmentation; and a triangular or wavering outline. Changes in the nail, such as fissuring or splitting, also are worrying, as is any associated discoloration of the periungual skin.
Dermoscopy may confirm the irregularity of the pigmentation pattern and show irregularly colored and spaced lines of varying thicknesses within the pigmented band. An LM caused by melanoma may also be marked by loss of parallelism within the pigmented band.
She pointed out that these concerning characteristics have been encapsulated in a mnemonic, first created in 2000, that’s meant to mirror the ABCDs of nonnail melanoma detection (J Am Acad Dermatol. Feb 2000;42[2 Pt 1]:269-74). Her survey found that overall, just one in four (24.8%) of respondents knew of the mnemonic for subungual melanomas.
Dr. Lipner reported that she has received research support from MOE Medical Devices and has served as a consultant to BAKO Therapeutics.
SOURCE: Lipner S. Summer AAD 2018, Presentation F004.