What is Longitudinal Melanonychia?

Definition of Longitudinal Melanonychia - Dark Streaks in Your Nails

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What causes dark streaks the length of your fingernail or toenail? Longitudinal melanonychia is the presence of a pigmented stripe, usually brown or black, along the length of the nail bed. They are common in darker-skinned individuals. Longitudinal melanonychia results from deposition of melanin in the nail plate from a variety of causes. A small number of people with longitudinal melanonychia have subungual melanoma.

Pronunciation: LAWN-ji-TOOD-in-ul MEL-uh-non-EE-ki-uh • (noun) 

What Causes Longitudinal Melanonychia?

Pigment in your nails is produced by cells called melanocytes in the nail bed. They produce melanin, the pigment that gives hair its color and produces a sun tan in your skin. In the nail bed, they transfer melanin to the cells that are producing the nail. When you see a dark stripe in your nail, it is where they are producing more melanin at the base and it creates a stripe as the nail grows outward.

The causes of melanonychia are divided into the categories of melanocytic activation, where the cells already present start producing more melanin, and melanocytic hyperplasia where more pigment-producing cells multiply.

Benign Causes of Melanocytic Activation

Most often you will see a dark streak in a single nail. In 73% of adult cases,  this is due to the cells already present producing more pigment.

Your racial skin color is a factor for this, as people with naturally dark skin often have longitudinal darker bands in their nails. You get more as you age, and they get wider. They happen most often on the fingers you use to grab hold of things - your thumb, index and middle finger.

Pregnancy is another time when you are more likely to see longitudinal melanonychia.

Trauma to the nail plate can cause it as well. If you see stripes on your little toe or big toe, it may be due to your toes banging against your shoes if they don't fit well.

Fungal infection of the nail can cause dark streaks, as can psoriasis, skin infection around the nail, amyloidosis, and lichen planus.It may also appear, often with multiple bands, in Addison's disease and AIDS.

Chemotherapy, X-rays and electron beam therapy can cause melanocytic activation, often on several nails. It can appear in Laugier-Hunziker syndrome, Peutz-Jeghers syndrome and Touraine syndrome.

Melanocytic Hyperplasia - Benign and Malignant Melanoma

Melanocytes can multiply and produce melanonychia in either benign or malignant conditions. Benign hyperplasia can be in lentigines (spots) or nevi (nests). In children, 77.5% of cases of melanonychia are due to benign melanocytic hyperplasia.

Malignant melanocytic hyperplasia may be due to invasive melanoma or in situ. It is most often seen in the thumb, big toe or index finger.

It occurs about as often in all racial groups, while melanoma in other sites is more rare for darker-pigmented races.

Diagnostic Tests in Melanonychia

To rule out melanoma, a biopsy is often done. The biopsy takes tissue from the nail matrix, which can result in scarring. This may not be what you want, but melanoma is a serious medical condition that will require treatment.


Julie Jefferson * and Phoebe Rich. "Melanonychia."Dermatol Res Pract. 2012; 2012: 952186. Published online 2012 Jun 27. doi: 10.1155/2012/952186. PMCID: PMC3390039

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