Longitudinal Melanonychia: Types, Causes, Risk Factors, Treatment

Melanonychia is the black and brown pigmentation in the nail plate. Longitudinal melanonychia is the most common type of melanonychia which shows up like partial or complete stripes running lengthwise along with the nail from the nail matrix to the free edge of the nail. Longitudinal melanonychia can occur due to pigmentation, infection, any disease in the body, or even due to cancer.

The color of skin, hair, and nails is produced due to pigment cells known as melanocytes, which produce melanin. Overproduction of melanin occurs in melanonychia and longitudinal melanonychia is a type.

Longitudinal melanonychia can vary depending on how the melanin overproduction occurs, which includes:⁽¹⁾

• Melanocytes activation: In this type, the melanocytes produce extra melanin
• Melanocytes hyperplasia: In this type, the melanocytes multiply abnormally

Melanocyte hyperplasia is a cause of concern as the melanocytes are more prone to genetic errors and can develop of benign or cancerous conditions.

Extra production of melanocytes is the most common cause of longitudinal melanonychia.

Melanin in the nail plate is evenly distributed but sometimes can get irregular. In longitudinal melanonychia, the pigment cells from the base of the nail bed transfer to the nail cells. As the nail grows the melanin will be carried along creating a length-wide strip from the nail fold to the cuticle.

There are numerous reasons that lead to its occurrence, and some are completely harmless.

Longitudinal melanonychia is more common in people of African descent. It can occur due to nail trauma, a nail infection, or any other disease of the body.

1. Nail Trauma

   Nail trauma, starting from the base of the nail, and subungual hematoma or blood under the nail are the common cause of longitudinal melanonychia. If someone gets hit by something hard on the nail, there will be the occurrence of bad bruises and also turns on the melanocytes at the nail bed. This leads to the collection of melanin in the nail cells and leads to blackish or grayish discoloration. This is known as melanocyte activation.

2. Infections

   Infections can also lead to longitudinal streaks, which may be fungal, viral, or bacterial. Different types of infections include:

   • Subungual verruca: It is a wart under the nail plate
   • Onychomycosis: It is a common nail infection
   • Chronic paronychia: It is a bacterial or fungal infection that occurs where the side of the nail meets the skin.

3. Autoimmune and Skin Condition

   Conditions affecting skin or nails can cause longitudinal melanonychia.

   In autoimmune conditions, the body’s immune system attacks its own tissues and cells.

   The conditions include:

   • Nail Psoriasis: It is an autoimmune condition that causes changes in the nail.
   • Addison’s Disease: It is an insufficiency of adrenal glands caused by autoimmune disease, cancer, infection, or pituitary tumors.
   • Lichen Planus: It is an inflammatory skin condition that occurs due to an autoimmune reaction.

4. Benign Growths

   When the nail cells multiply abnormally, the condition is often benign.

   Common types of benign growths that can lead to longitudinal melanonychia are:

   • Pyogenic Granuloma: These are the blood-red skin growths that occur in pregnancy or as a side effect of a certain condition
   • Subungual Exostosis: It is a bony overgrowth at fingertips and toes caused due to bone irritation.⁽²⁾
   • Myxoid Cyst: These are small benign lumps that occur near the nail

5. Cancer

   Sometimes neoplasms or growth causing longitudinal melanonychia are cancerous. They may include:

   • Subungual Melanoma: It is a dangerous type of skin melanoma occurring under the nail plate.
   • Glomus Tumor: It is a deadly tumor found under the nail, on the fingertip, or at the end of the toe.
   • Keratoacanthoma: It is a low-grade dome-shaped tumor that is found on the sun-exposed skin and can lead to longitudinal melanonychia.⁽³⁾

6. Environmental Causes

   Longitudinal melanonychia occurs when pigment deposits in the nail bed. These can be absorbed by the cuticle and underlying nail cells and carried to the nail plate as the nail grows.

   The environmental causes include:

   • Ink
   • Tar deposits
   • Hair dyes
   • Silver nitrate
   • Potassium peroxide

The treatment of melanonychia depends on the cause and may include:

• Antifungal or antibiotics if an infection is a cause
• Treating the underlying medical condition

If longitudinal melanonychia is due to a cancerous condition the tumor or the cancerous area may have to be completely removed. It can also mean a person losing all or a part of the nail. In some cases, if the condition involves the finger, the whole finger may need to be amputated.

Longitudinal melanonychia occurs due to overproduction of melanin or due to an increase in the melanocytes. There are many reasons for its occurrence ranging from harmless growth to cancer.

Whatever is the cause it is safe to consult a healthcare provider as early treatment can make a huge difference.