Causes and risk factors of longitudinal melanonychia

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Melanonychia is the medical term used to describe the black or brownish pigmentation of the nail plate. The most common type is longitudinal melanonychia, characterized by the appearance of a pigmented strip (partial or complete) along the nail bed.

Longitudinal melanonychia is common in people of African descent, but it can also be caused by trauma to the nails or a systemic disease. Other causes include nail infections and cancer.

A rare form of melanonychia called transverse melanonychia is recognized by a dark line running from side to side along the nail plate. Transverse melanonychia is generally associated with certain medications and radiation therapy .

Common causes

Nail, hair, and skin color is determined by cells known as melanocytes , which secrete a pigment called melanin. Although melanin is generally evenly distributed on the nail plate, it can sometimes become uneven.

For example, if you hit a nail with a hammer, you can not only cause a bruise (bruise), but you can also activate the local melanocytes in the nail bed. When this happens, melanin accumulates in the damaged cells of the nail (onychocytes), causing a blackish or grayish discoloration. This is similar to how freckles darken when the sun's ultraviolet rays activate the melanocytes in the skin.

In longitudinal melanonychia, melanocytes at the base of the nail transfer melanin to local onychocytes. As the nail grows outward, the melanin will be removed, forming longitudinal (longitudinal) stripes on the cuticle (nail fold). This can happen for many reasons, some of which are completely harmless.

Rytis Bernotas / Getty Images

Common reasons include:

  • Trauma to the nail (usually begins at or near the base of the nail)
  • Subungual hematomas (blood under the nail)
  • Subungual wart (wart under the nail plate)
  • Onychomycosis (a common fungal infection of the nails)
  • Nail psoriasis (an autoimmune disease)
  • Lichen planus (an inflammatory skin disorder believed to be autoimmune)
  • Chronic Paronychia (bacterial or fungal infection that occurs where the side of the nail meets the skin)
  • Pyogenic granuloma (blood-red skin growths that sometimes occur during pregnancy or as a side effect of certain medications)
  • Addison's disease (adrenal insufficiency caused by an autoimmune disease, cancer, infection, or tumors of the pituitary gland)
  • Subungual exostosis (excessive growth of the tips of the fingers or toes, possibly caused by persistent irritation of the bones.

How to determine the goodness of the cause.

Benign longitudinal melanonychia can be recognized by the appearance of light to dark brown stripes, parallel and regular in color, thickness, and distance. The border will be clearly marked and less than 3 millimeters (mm) wide, or approximately 1/10 of an inch.

Another good quality sign of longitudinal melanonychia is yellowish fading along the periphery of the stripe. Melanonychia caused by a serious illness usually does not go away.

Also, if a blackish mark is caused by injury, it will tend to move towards the tip as it grows, leaving a flawless nail.

Genetic causes

Longitudinal melanocytosis is a symptom of several rare genetic diseases in which hyperpigmentation of the skin is a common symptom. Many of these conditions are autosomal dominant , which means that you only need to inherit one genetic mutation from one parent for the disease to manifest.

Examples include:

  • Familial amyloidosis (a rare and life-threatening condition that occurs when a protein called amyloid accumulates in organs and tissues )
  • Lodge-Hantsiker syndrome (a rare condition characterized by hyperpigmentation of the mouth, lips, fingers, and nails, and a high risk of cancer )
  • Peitz-Jeghers syndrome (a rare condition manifested by benign polyps in the gastrointestinal tract and hyperpigmented rashes in the mouth, lips, nails, and fingers )
  • Touraine syndrome (a rare and non-progressive disease characterized by scant body hair, brittle teeth, decreased ability to sweat, and hyperpigmented lesions )

Cancer

The causes of longitudinal melanonychia fall into two categories: melanocyte activation (in which the melanocytes produce additional melanin) and melanocyte hyperplasia (in which the melanocytes proliferate abnormally) .

The latter is especially important since melanocytes are prone to genetic errors during reproduction, which can lead to the development of benign or malignant skin neoplasms known as neoplasms .

Among the neoplasms that can cause longitudinal melanonychia, the following can be distinguished:

  • Glomus tumor (a rare and life-threatening tumor found mainly under the nail, on the tip of a toe, or at the end of a toe)
  • Keratoacanthoma (a low-grade domed tumor usually found on sun-exposed skin)
  • Myxoid cysts (small, benign growths near the nail)
  • Subungual melanoma (the deadliest form of skin cancer that occurs under the nail plate )

Longitudinal melanonychia in children is extremely rare. When this happens, 77.5% will be the result of benign melanocytic neoplasms .

Subungual melanoma

Subungual melanoma mainly affects people over 50 years of age and is considered rare, accounting for 0.7% to 0.35% of all skin cancers .

In a physical exam of the nail, the doctor will look for certain tell-tale signs of cancer:

  • Damage to more than two-thirds of the nail plate
  • Gray or black with a hint of brown
  • Irregular brown and grainy pigmentation
  • Band thickness and color variations
  • Blurred edges greater than 3mm
  • Distortion of the nail plate.
  • Recurrent spontaneous bleeding at the same site

Subungual melanoma often affects one finger rather than several. Other symptoms may include longitudinal stripes on the affected toe or foot and darkening of the palms or soles of the feet.

One of the key signs of subungual melanoma is Hutchinson's sign. This is when the strip extends from the tip of the nail to the nail bed and cuticle .

Subungual melanoma can only be accurately diagnosed with a nail biopsy . People with melanoma of the nail matrix tend to do poorly.

DermNet / CC BY-NC-ND

Environmental causes

Longitudinal melanonychia can develop when pigments other than melanin are injected into the nail fold. They can be absorbed by the cuticle and underlying onychocytes and transferred as the nail plate grows.

Common examples include:

  • ink
  • Tar deposits from repeated smoking
  • Hair dyes or henna, mascara,
  • Potassium permanganate (topical disinfectant)
  • Silver nitrate is used to treat burns and wounds.

The cuticle exam, along with a review of your medical history, can help differentiate these environmental causes from other more serious conditions.

If the cause is environmental, the streak usually does not extend beyond the lunula (a whitish sickle at the base of the nail). There may also be discoloration under the crease of the nail and the edge of the surrounding skin.

Get the word of drug information

A dark streak on your nail bed can be worrisome, but it doesn't necessarily mean you're sick or at risk of getting sick. At the same time, this is not something you should ignore, especially if the condition is persistent, affects most of the nail, or is associated with bleeding.

The cause of melanonychia can usually be diagnosed by a dermatologist . If there are suspicious signs, the doctor may take a small sample of the nail for laboratory tests. If a problem is found, early diagnosis and treatment will almost always lead to better results.

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