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  • Presentation

When to Biopsy Melanonychia: Distinguishing Benign from Malignant Nail Pigmentation

Description

The talk reviews how to evaluate melanonychia and when to biopsy to avoid missing nail malignancy. The first step is determining whether pigmentation affects one digit or multiple digits; polydactylous cases prompt a broad history, exam for other lentigines, and search for an “ugly duckling,” while monodactylous cases require careful consideration of both melanocytic and non-melanocytic causes such as fungus, exogenous pigment, hemorrhage, pigmented Bowen disease/squamous cell carcinoma, nevus, lentigo, melanocytic activation, and melanoma. Dermoscopy, serial photographs, nail clippings, and biopsy are key tools. Nail clippings can reveal fungal elements, dried blood, or melanocyte remnants that may raise concern for melanoma and help counsel hesitant patients. Dermoscopic clues discussed include homogeneous gray or tan backgrounds for activation, reverse triangle sign and distal pigment prominence for fungal melanonychia, and globular/shaggy or geometric patterns for subungual hemorrhage. Age strongly influences management: childhood monodactylous melanonychia is usually benign and is often monitored unless rapidly proliferative or peripubertal, whereas adults with a single pigmented band should generally be considered malignant until proven otherwise, especially if the thumb or great toe is involved, the band is widening/darkening, or there is periungual pigmentation/Hutchinson sign. However, appearance alone is unreliable because benign and malignant lesions can look similar; several cases showed melanoma, severe atypia, lentigo, or activation despite misleading clinical patterns. The presenter emphasizes that when clinical and pathology findings disagree, the clinical concern should guide further action, and clinicians should seek training or refer to nail experts when biopsy skills are limited.

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Conclusions

  • Dark nail pigmentation should be approached by first distinguishing monodactylous from polydactylous involvement and by looking for an ugly-duckling pattern, because the differential includes both benign and malignant causes.
  • In polydactylous melanonychia, clinical context, medication and medical history, and the presence of an underlying cause are key clues, but biopsy is still warranted when one digit looks different from the rest.
  • Nail dermoscopy, serial photographs, and nail clippings are valuable tools for sorting out pigmented nail lesions and can sometimes prevent unnecessary surgery or support the decision to biopsy.
  • Nail clippings can identify fungus, blood, or even melanocyte remnants, and in adults the finding of melanocyte remnants may raise concern for occult melanoma.
  • Fungal melanonychia and pigmented onychomycosis can mimic melanocytic disease, but they tend to look more homogeneous and may show signs such as the reverse triangle pattern.
  • Subungual hematoma is usually suggested by globular, shaggy, geometric pigment that grows out over time, and clipping or follow-up imaging can confirm the diagnosis without immediate biopsy.
  • Because many monodactylous nail bands cannot be reliably distinguished by appearance alone, a low threshold for biopsy is appropriate, especially for the thumb and great toe.
  • Age strongly influences risk: pigmented nail bands in children are usually benign, whereas lesions in adults, particularly over 40, should be treated as malignant until proven otherwise.
  • Peripubertal or rapidly changing pediatric nail pigmentation deserves closer evaluation and sometimes excision, but childhood lesions are still overwhelmingly benign overall.
  • Even a bland-appearing adult nail band can harbor invasive melanoma, so clinical suspicion should not be lowered just because the lesion looks subtle.
  • The clinical and pathologic impressions must be reconciled carefully, but when they disagree, the clinical picture may deserve greater weight and repeat sampling can be justified.
  • Education, training, and access to nail specialists improve clinicians’ comfort with nail surgery and biopsy, and referral to an expert is appropriate when needed.
  • Clinical and Experimental Dermatology (2015) 40, pp271-278.
  • Stiff KM, Jellinek NJ, Knackstedt TJ. Dermatol Surg. 2021;47(12):1670-1671. PMID: 34743121.