Melanonychia is a condition of either the fingernails or the toenails. Melanonychia is when you have brown or black lines on your nails. The decolorization is usually in a stripe that starts at the bottom of your nail bed and continues to the top. It may be in one nail or several. These lines can be a natural occurrence if you have a dark complexion.

No matter what the cause may be, you should always have a doctor check any melanonychia. This is because it can sometimes be a sign of other health issues. Melanonychia may also be called melanonychia striata or longitudinal melanonychia.

There are two broad types of melanonychia:

  • Melanocytic activation. This type is an increase in the production and deposits of melanin in your nail, but not an increase in pigment cells.
  • Melanocytic hyperplasia. This type is an increase in the number of pigment cells in your nail bed.

The nails of your toes or fingers are usually translucent and not pigmented. Melanonychia is caused when the pigment cells, called melanocytes, deposit melanin into the nail. Melanin is a brown colored pigment. These deposits are usually grouped together. As your nail grows, it causes the stripe of brown or black to appear on your nail. These melanin deposits are caused by two primary processes. These processes have different causes.

Melanocytic activation can be caused by:

Melanocytic hyperplasia may be caused by:

  • lesions (usually benign)
  • moles or birthmarks (usually benign)
  • cancer of the nail

Other causes of melanonychia beyond the two primary types may include:

  • some bacteria
  • tobacco
  • hair dye
  • silver nitrate
  • henna

People of African descent are the most likely to experience melanonychia.

The treatment for melanonychia varies depending on the cause. If your melanonychia is from a benign cause and is noncancerous, then many times, there is no treatment needed. If your melanonychia is caused by medication, your doctor may change your medication or have you stop taking it for a time, if that is possible. For medications that you cannot stop taking, melanonychia will just be a side effect for you to get used to. Other treatment options depend on the cause and may include:

  • taking antibiotic or antifungal medications, if an infection is the cause
  • treating the underlying disease or medical condition causing the melanonychia

If your melanonychia is malignant or cancerous, then the tumor or cancerous area must be completely removed. The may mean that you’ll lose all or part of your nail. In some cases, the finger or toe that has the tumor may have to be amputated.

A diagnosis of melanonychia is reached after a series of diagnostic exams and tests. Your doctor will begin with a physical exam of all your fingernails and toenails. This physical exam includes looking at whether your nail is deformed in any way, how many nails have melanonychia, as well as the color, shape, and size of your melanonychia. Your doctor will also look at your medical history to see if you have any medical conditions that may be causing the melanonychia.

The next step in diagnosis is a dermatoscopic examination using a specific type of microscope to get a close look at the discolored areas. Your doctor will look primarily for signs that your melanonychia may be malignant. The signs of possible nail melanoma are:

  • over two thirds of the nail plate is discolored
  • brown pigmentation that is irregular
  • black or grey color with the brown
  • granular looking pigmentation
  • deformity of the nail

Besides looking for signs of a possible melanoma, your doctor will combine findings from both the dermoscopy and the physical exam to determine the type and cause of your melanonychia.

After these two steps, your doctor may also perform a biopsy of your nail. A biopsy removes a small portion of your nail and nail tissue for examination. This step will be done in most cases of melanonychia unless there are no possible signs of cancer. A biopsy is an important step in the diagnosis of melanonychia because it will tell your doctor with certainty if it’s malignant or not.

Possible complications of melanonychia include nail cancer, bleeding under the nail, splitting of your nail, and deformity of your nail. The nail biopsy can also cause nail deformity because it removes a portion of the nail.

The outlook for most benign melanonychia is good, and in most cases, does not require treatment. However, it usually does not go away by itself.

The outlook for malignant melanonychia is not as good. This condition requires the removal of the tumor which may also include amputation of your finger or toe. Cancer of the nail is challenging to catch in the early stages because of its similarities to the benign causes of melanonychia. Research has found that performing a biopsy on most melanonychia is the best way to get an earlier diagnosis.