Hyperpigmentation is a situation in which a person has too much pigment. Most of the time, the excess pigment is in the skin, where a person with hyperpigmentation produces too much melanin. Hyperpigmentation of the nails can also occur. This medical condition is called melanonychia striata. Melanonychia striata is classified as a nail deformity, but most of the time does not indicate a serious health threat.
Melanonychia striata can occur for a variety of reasons. A case study reported in the June, 2008 issue of the "Journal of the American Medical Association" (JAMA) showed several members of the family experienced hyperpigmented areas of their nails, suggesting that the condition is inherited. Addison's disease, post-inflammatory hyperpigmentation of the skin, pregnancy and melanoma can also lead to hyperpigmentation in the nails. Trauma to the hands and nails and use of medications, such as AZT, may also be causes, according to the Merck Manual.
Bands of hyperpigmentation in finger or toenails are more likely in people who have darker skin, according to a September 2004 JAMA article. One study reported in the article found that upon examination of more than 600 white subjects, none of them had discoloration of the nails. Different studies in the article reported that between 11 and 23 percent of Japanese participants were found to have some form of melanonychia striata. African Americans and other people with dark skin have a higher risk of hyperpigmentation as well. As suggested in the June 2008 JAMA, multiple people in the same family may be more likely to develop the condition. Nail discoloration of this kind is more prevalent as people age.
Signs and Symptoms
Hyperpigmentation of the nails usually appears as dark brown marks. The strips or bands of color run lengthwise across the nail. Melanonychia striata can affect one nail only, or several. Both hands and feet can be affected at the same time. For reasons that are not clear, fingers that are used frequently, such as on the dominant hand, are more likely to contain areas of discoloration. The condition is usually painless.
Most of the time, hyperpigmentation is not dangerous to the health. Treatment may not be required, though patients may be advised to notify their doctor if the dark bands begin to spread in size, or change in color. The exact cause for the hyperpigmentation may determine the course of treatment; for example, taking vitamin B12 supplements may be recommended if a deficiency is found to be the likely root of the problem. Changing medications that have prompted the discoloration can help control the issue as well.
Some types of nail hyperpigmentation can signify a more serious condition--a melanoma, or cancerous growth--in the nail. The Merck Manual states that melanoma of the nail is more likely if the band of increased pigment extends down through the cuticle of the nail as well as the nail itself. Biopsies and examinations of lymph nodes as well, can determine if cancer is present, and can determine the appropriate form of treatment.