When A Patient Presents With Longitudinal Nail Pigmentation
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
Longitudinal melanonychia associated with inflammatory nail disorders. This type of nail pigmentation occasionally develops in nails affected by lichen planus, onychomycosis, chronic radiodermatitis, pustular psoriasis or Hallopeau’s disease. The pigmentation can be subtle at the beginning and become clearly clinically evident as the inflammatory process progresses. It is usually associated with nail scarring and abnormalities of the surface of the nail plate.1