When A Patient Presents With Longitudinal Nail Pigmentation

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Nail Pigment Changes That Should Undergo Biopsy

1. Isolated pigmented band on a single digit that develops during fourth to sixth decade of life (although melanoma can occur in children, it is a very rare event)
2. Nail pigmentation that develops abruptly in a previously normal nail plate
3. Pigmentation that suddenly becomes darker or larger, or pigment becomes blurred near nail matrix
4. Acquired pigmentation of thumb, index finger, or large toe
5. Pigment that develops after a history of digital trauma and in which one has ruled out subungual hematoma
6. Any acquired lesion in patients with a personal history of melanoma
7. If pigmentation is associated with nail dystrophy including partial nail destruction or absence of nail plate
8. If pigmentation of periungual skin (including lateral nailfolds) is found to be present (Hutchinson’s sign); this includes pigment of cuticle or hyponychium

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Author(s): 
M. Joel Morse, DPM

   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

   Nail dystrophy. Nail dystrophy is rare in racial melanonychia but common in traumatic and fungal melanonychia. Nail dystrophy occurs in squamous cell carcinoma and benign melanocytic hyperplasia, but does not occur with melanoma.

   Number of nails affected. Racial melanonychia usually occurs in two to five nails and to a lesser extent in one nail or all 10 toenails. Traumatic melanonychia usually affects one nail. Fungal melanonychia is usually present in two to five nails. In their study, Dominguez-Cherit and colleagues noted that squamous cell carcinoma, benign melanocytic hyperplasia and melanoma always occurred in one nail or two to five nails but never all 10 nails.8

A Guide To The Differential Diagnosis

Fungal melanonychia. Fungal melanonychia shares some characteristics with racial melanonychia, such as the different shades of brown color, width less than 4 mm and frequent involvement of more than one nail. Nail dystrophy seems to be the most important clinical sign to distinguish between these two types of melanonychia. It is common in fungal melanonychia and rare in racial longitudinal melanonychia.9

   Distal lateral subungual onychomycosis remains the most common form of fungal invasion of the nail plate, where the site of invasion is from the lateral or distal undersurface of the nail plate. The main features are onycholysis with hyperkeratosis and varying forms of dyspigmentation. Most commonly, this is white or yellowish but on occasion, other color changes can occur such as brown, black and orange discoloration.10

   Nutritional longitudinal melanonychia. Pigmentation of the nails and the skin can happen with vitamin B12 or folate deficiency.1 The pigmentation tends to have a bluish-black color. The pigmentation on the skin is accentuated over the knuckles and the distal phalanges. Usually, one diagnoses this based on laboratory examination. This type of nail pigmentation is completely reversible after vitamin B12 or folate administration.1

   Traumatic longitudinal melanonychia. In frictional melanonychia, repeated rubbing, trauma and friction stimulate matrix melanocytes to produce more pigment. Repeated trauma such as nail biting may induce nail pigmentation.11 We mainly see this as a result of shoes that are too small, hammertoes in a shoe with a shallow toebox, an excessively long second toe in which the nail is at a right angle to the ground, or an adductovarus fifth toe.

   It mainly arises on the toes and is often associated with foot deformities, inadequate footwear or both. This type of nail pigmentation may gradually fade once the repetitive trauma has subsided.11

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