Dr. Ata Moshiri highlights his lecture Melanonychia: When to Biopsy & How to Decide at the 2nd Annual Elevate-Derm Alliance Summer Conference in Park City, Utah at the Grand Hyatt Deer Valley.

In this video

Dr. Moshiri outlines the features that make his "blood pressure go up" with melanonychia: a single affected digit (multiple longitudinal brown lines are very unlikely to be cancer), older age with new onset, and band characteristics — thick bands with multiple colors are far more concerning than thin, faint, uniform ones. He flags the triangle sign (a band that widens toward the base as a matrix lesion grows), the Hutchinson sign (pigment extending onto the nail folds or hyponychium), and location, noting nail unit melanoma most often appears in the thumb or great toe and is rare in the fifth digit.

On technique, he stresses that the nail is different from anywhere else on the skin: the pigment is made by the matrix living under the proximal nail fold, so going straight through the band into the nail bed almost always misses the diagnostic tissue. A proper nail matrix biopsy — reflecting back the nail fold to expose the matrix — is critical, and he warns against the tempting pitfall of grabbing pigmented nail fold skin (Hutchinson sign), where the melanoma frequently isn't present. For a borderline lesion he'd monitor at a three-month interval, reasoning that fingernails take about six months to grow out (toenails a year or more), so substantial change can appear quickly.

  • A single affected digit, older age with new onset, thick multicolored bands, the triangle sign, and the Hutchinson sign all raise concern; multiple faint uniform longitudinal bands are reassuring.
  • Nail unit melanoma most commonly appears in the thumb or great toe (hallux) and is rare in the fifth digit.
  • Biopsy the nail matrix under the proximal nail fold — not the nail bed beneath the band — or you can miss the diagnostic tissue and delay diagnosis.
  • Don't be fooled by pigmented nail fold skin (Hutchinson sign); the melanoma often isn't present there, so go for the matrix under the longitudinal streak.
  • When monitoring a borderline lesion, use short intervals — no longer than three months — since half a fingernail can grow out in that time.