LONGITUDINAL MELANONYCHIA

By Gary M. White, MD

Longitudinal Melanonychia Any pigmented streak of the nail must be carefully evaluated.


Longitudinal melanonychia (LM) may be defined as a longitudinal pigmented streak of the nail caused by melanin in the nail plate.

Causes of LM by Activation

Causes of LM by Proliferation

Causes of Dark Streaks of the Nail That Are Not LM

In one study of 40 children with LM [JAAD 1999;41;17], the cause in 19 was a nevus, in 12 a lentigo, and in 9 functional LM. See pigmented streaks of the nail.

Clinical

A longitudinal brown streak of the nail is seen. The origin is the base of the nail (proximal nail fold) and the width of the pigmentation is uniform. (Rarely, with rapidly growing lesions, the width may be progressively wider proximally, giving what is called the "triangular sign".) This reliable and distinct pattern helps distinguish LM from subungual hematoma or darkening from onychomycosis. Those patterns of darkening are random, haphazard and often not contiguous with the proximal nail fold.

Pigmentation of the proximal or lateral nail folds, and hyponychium (Hutchinson's sign) can be a sign of melanoma but is not uncommon in benign LM, especially in children [JAAD 2016;75;535]. Complete darkening of the nail is called total melanonychia.

Nail clipping with special stains can be used to confirm that the pigment is melanin.

In one case, a 52-year-old woman presented with multiple longitudinal pigmented bands of melanonychia of the finger and toes. Other nails had a diffuse gray-black pigmentation. The cause turned out to be an ACTH-producing pituitary adenoma [CED 2013;38;689].

Dermoscopy

Differential Diagnosis

See here for a differential.

To Biopsy or Not to Biopsy

Biopsy is in order for any new, solitary lesion with suspicious features, especially in an adult. Worrisome features include width greater than 6 mm, multiple colors, or dark black. Pigmentation of the proximal nail fold--Hutchinson's sign--is particularly worrisome.

In one study of pigmented nail bands [JEADV 2017 31;732], key features that suggested melanoma included:

Granular pigmentation, a newly defined dermoscopic criterion, was found in 40% of melanomas and only in 3.51% of benign lesions.

Children

For children--because childhood subungual melanoma is extremely rare--photodocumentation to help monitor the lesion is reasonable, unless there is rapid growth, many fine, dark longitudinal lines within a wider, lightly-pigmented streak or significant variation in pigmentation. In these or other high-risk situations, biopsy should be performed. One paper failed to find a single case report of melanonychia striata that resulted from an invasive melanoma in a child [JAAD 2015;72;773]--although melanoma in situ causing LM has been reported.

Biopsy Technique

One approach is to completely remove all the nail covering the streak and send that for pathology as invariably some of the nail bed will be stuck to the plate. Then do an ellipse longitudinally including the proximal start of the streak. Close as best as you can with a few stitches. Schedule 45 minutes; don't rush.

Another option is outlined in this article, Derm101, with good pictures for biopsy. In summary:

Treatment

Treatment depends upon the cause.

Additional Pictures

Longitudinal Melanonychia Longitudinal Melanonychia

Multiple streaks in multiple nails tends to be benign.
Longitudinal Melanonychia

A rare case of a nevus of the nail bed causing LM. Biopsy was read out as nevus with atypia.
Nevus (mole) of the nail bed causing Longitudinal Melanonychia Nevus (mole) of the nail bed causing Longitudinal Melanonychia

This new, single, very dark black streak was on biopsy a melanoma in situ.
Melanoma in situ causing Longitudinal Melanonychia

Here, a punch biopsy of the above melanoma in situ of the nail apparatus is shown.
Punch biopsy of the Nail Bed for Longitudinal Melanonychia

A pigmented streak not caused by a nail matrix nevus, but instead by onychomycosis.
onychomycosis causing a pigmented band of the nail

References

Heavily pigmented subungual lentigo in a child. JAAD 2015;72;773–779

Subungual congenital nevus in a child. JAAD 2015;72;773–77

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