When A Patient Presents With Longitudinal Nail Pigmentation

M. Joel Morse, DPM

   Melanonychia is defined by the presence of melanin within the nail plate. It appears more often as a longitudinal brown-black band starting from the matrix and extending to the free edge of the nail plate. Less often, the pigmentation can involve the whole nail plate or present as a transverse band.2 There are many causes of discoloration of the nail plate.

   Melanonychia results from production of melanin by melanocytes of the nail matrix, where melanocytes are usually quiescent but may become active and start melanin synthesis. Melanonychia has four main causes: simple melanocytic activation; increased activation (with a normal number) of melanocytes; benign melanocyte proliferations (lentigo, nevus); and malignant melanocyte proliferation (melanoma). When matrix nevi present as melanonychia, the pigment producing nevus cells incorporate melanin into the nascent nail plate onychocytes, producing true brown nail plate discoloration.4

   Simple melanocyte activation can occur as melanotic macules. Melanotic macule of the nail unit, a benign condition resulting from an increase in production of melanin by melanocytes in the matrix, is the most common cause of a pigmented longitudinal band of the nail plate in adults.­5

   Less commonly, melanonychia due to melanocytic activation can result from inflammatory and traumatic nail disorders, fungus and drugs (chemotherapy, azidothymidine (AZT), anti-malarials, photochemotherapy).6 It may also be due to systemic diseases, such as Laugier-Hunziker and Peutz-Jeghers syndromes, HIV infection, acanthosis nigricans and even lupus and scleroderma, as well as cutaneous disorders such as psoriasis and lichen planus.7

   More commonly, melanonychia results from melanin produced by melanocytes in the matrix and may be a normal variant in darker-skinned people. Longitudinal melanonychia occurs with melanocytic macule, junctional or compound melanocytic nevus, or melanoma.5 Differentiating among these can be difficult.

   One way to view longitudinal melanonychia is that of a streak in the nail plate with normal nail surrounding it. Another way to view it is as a extra wide streak that is so wide that it comprises the entire nail plate.

Pertinent Diagnostic Considerations In Assessing Racial Melanonychia

In regard to racial melanonychia, clinicians should consider the color of pigment, band width, nail dystrophy and the number of nails affected.

   Color of pigment. Brown or black discoloration of the nail can represent a wide variety of disorders, the majority of which are benign.8 The color is normally light brown, dark brown, black or variegated. When it comes to racial melanoychia in the Hispanic population, the color is usually light or dark brown 97 percent of the time.8 Trauma, with underlying hematoma, remains the most common cause of melanonychia and is usually dark brown or black. Fungal melanonychia is either light brown, dark brown or variegated, and almost never black.

   Melanonychia width. Many studies use the following measurements: 1 to 3 mm wide, 4 to 6 mm wide and full width of the nail. One hundred percent of the nails diagnosed with racial melanoychia were 1 to 3 mm or 4 to 6 mm in width.8 Traumatic and fungal nails had a 1 to 3 mm melanonychia width. Squamous cell carcinoma, benign melanocytic hyperplasia and melanoma were always in the 4 to 6 mm range and full width measurement in terms of melanonychia width.8

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