When A Patient Presents With Longitudinal Nail Pigmentation

M. Joel Morse, DPM

   Longitudinal melanonychia due to drugs. Several drugs may activate clusters of nail matrix melanocytes to produce melanin, giving rise to the appearance of a band of melanonychia or multiple longitudinal or transverse bands ranging in color from light brown to black.12 In drug-induced melanonychia, several nails are generally affected with multiple bands. In some cases, only one digit is involved.

   A diffuse activation of nail matrix melanocytes produces pigmentation of the whole nail plate. Drug-induced melanonychia most commonly appears three to eight weeks after drug intake.1 Pigmentation is usually reversible within six to eight weeks but may persist for months after drug interruption.1

   Drugs that may cause melanonychia include zidovudine (Retrovir), chemotherapy agents, hydroxyurea (Hydrea) and psoralens. Radiation therapy for malignant disease far from the digit can also cause longitudinal melanonychia.3

When Should You Biopsy?

Doctors are often unsure regarding their clinical diagnosis and lack confidence in managing this condition. Furthermore, many physicians are also reluctant to perform biopsies of the nail matrix because the procedure is painful and can result in permanent nail dystrophy. To complicate matters, when a physician finally decides to biopsy, it is not uncommon for one to submit inadequate biopsy specimens (e.g., biopsy specimen of the nail plate instead of the nail matrix) to the pathologist. This subsequently compromises the ability of the pathologist to render an accurate diagnosis.1

   I recommend a nail matrix biopsy of pigmented nail lesions in the following cases:
• when the entire nail is involved;
• when there are variegated colors from light or dark brown to black;
• when the pigmented band has had recent color; or
• when there are width changes in Hispanic patients who have a newly acquired longitudinal melanonychia, even if more than one nail is affected, regardless of the age group.9

In Conclusion

Given the fact that the population of people with pigmented skin is increasing in the world, it is incumbent on us to understand nail pathology in those individuals. When it comes to the differential diagnosis, it is essential to be aware that there is much overlap between benign nail pigmentation and subungual malignant melanoma.

   Dr. Morse is the President of the American Society of Podiatric Dermatology. He is a Fellow of the American College of Foot and Ankle Surgeons, and the American College of Foot and Ankle Orthopedics and Medicine. Dr. Morse is board certified in foot surgery. He is on the Podiatric Residency Educational Committee at the Washington Hospital Center in Washington, D.C.

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