CHICAGO – A discolored nail can give even seasoned dermatologists pause: Is the cause exogenous? Fungal or bacterial, perhaps? Could it be a subungual melanoma? Should it be followed, clipped, or biopsied? of the American Academy of Dermatology summer meeting.
Dr. Shari Lipner
The session came after a recent nationwide survey performed by Dr. Lipner and her collaborators who asked dermatologists at different practice stages how confident they were in the diagnosis and management of melanonychia. “On the whole, they were not very confident at all,” said Dr. Lipner, director of the nail division at Cornell University, New York.
Of 142 dermatology residents, as well as 58 junior and 199 senior attending dermatologists, just 18.2% performed nail exams at each visit, and most (58%) only looked at nails during the total body skin exam. Over half (62%) of resident physicians reported feeling not confident about melanonychia diagnosis and management, while that figure dropped to 8.6% for senior attending physicians. Still, most senior physicians (64.3%) were just “fairly confident” in their melanonychia skills (J Am Acad Dermatol. 2017 May;76[5]:994-6).
Tools of the trade
Dermoscopy can be an invaluable tool for determining the cause of longitudinal melanonychia (LM). “Contact dermoscopy is helpful, so I always have ultrasound gel available,” Dr. Lipner said. “The gel makes the nail more of a flat surface,” which makes accurate viewing easier. Other useful tools include a double-action nail clipper, which, she said, is a worthwhile investment.
Because patients who are concerned about one of their nails will often come to their appointment with nail polish still on the other nails, Dr. Lipner always has polish remover pads available in the office. It’s important to be able to see all nails, she said, but she and her collaborators, including first author Pierre Halteh, MD, who was then a medical student at Cornell, discovered from their survey that “few physicians (32/402; 8%) asked their patients to remove nail polish at every visit.”
Nonmelanocytic causes of LM
Longitudinal melanonychias can have a nonmelanocytic etiology, which can range from subungual hematomas to pseudomonas and fungal infections to exogenous pigment.
Overall, subungual hematomas are the most common cause of melanonychia, although longitudinal hematomas are not commonly seen. The more remote the causative trauma, the darker the subungual discoloration, Dr. Lipner said. “Dermoscopy is very helpful” for subungual hematomas, which will usually show a homogeneous pattern, although “you can also see peripheral fadings, streaks, and periungual hemorrhages,” she added.
It is important to monitor these patients “because melanomas can bleed,” she said. In-office photography, or even pictures taken by patients, can be used to track the hematoma to resolution.
When thinking about exogenous sources of pigment, in addition to clues from the history, a tip-off can be that the proximal nail fold is also discolored, Dr. Lipner pointed out. A wide variety of common and less-common culprits may crop up, including from tar, tobacco, henna and other hair dyes, potassium permanganate, and even newspaper print, she said. With an exogenous source, careful clinical and dermoscopic examination may show that the pigment does not extend all the way proximally to the lunula, although it may follow the outline of the proximal nail fold.
When fungus is the cause of LM, the band is often wider proximally and tapers distally, Dr. Lipner noted. While Trichophyton rubrum var. nigricans is a known culprit, nondermatophytes, such as Neoscytalidium dimidiatum, can also cause an LM that often runs along the proximal and lateral nail folds. “To make the diagnosis, sending a clipping to the dermatopathologist is helpful,” she said. Hyphae can often be seen on staining and culture, she said. Polymerase chain reaction “is also possible and very helpful for these nondermatophytes.”
Bacterial colonization of the nail bed can be a cause of LM. Pathogens can include Pseudomonas aeruginosa, which will often show the characteristic greenish tint. Klebsiella and Proteus species may result in more of a grayish-black discoloration. A history of wet work, such as farming and other agricultural and dairy occupations, as well as housekeeping work, increases the risk for bacterial colonization.
Commonly, a bacterial etiology will result in discoloration beginning at the lateral nail fold or at the juncture of the proximal and lateral nail folds. Dermoscopy will show irregular fading of the discoloration toward the medial aspect of the nail, and gram staining of affected clippings will show gram-negative rods.