Light Brown Lines under Nail

This post is a response by a doctor to a question one of our community members asked.

Danish Asks:

I have two very thin light brown lines running parallel to each other from top of my finger nail to the bottom on finger nail. They been there for past 4 5 years and the size has never changed with time. I recently read an article about melanoma so I just worried if its just normal or something to worry about? I’m 27 years old of South Asian background. Thanks in advance.

Dr Alejandro’s reply:

Brown nail lines, medically known as melanonychia, are characterized by a brown to black discoloration of a nail (either finger or toe nail) and describes a pigmented band due to melanin (which is a dark natural pigment) deposit within the nail plate (the hard and transparent part of the nail). Melanonychia commonly presents as pigmented band arranged lengthwise along the nail unit, and this presentation is known as longitudinal melanonychia (LM) or melanonychia striata.

It is caused by an activation or hyperplasia (growth) of nail matrix melanocytes (which results in an increased production of melanin. Longitudinal melanonychia may appear as a single band involving one nail or as multiple band affecting several nails (most commonly seen in dark skin tones). Longitudinal melanonychia is most often benign and arises from a pigmented melanocytic nevus (a mole) or a lentigo (a freckle). A variety of other causes includes physiologic longitudinal melanonychia, systemic disorders, trauma, inflammatory disorders, fungal infections, nail biting, radiation therapy, ultraviolet light, malnutrition, vitamin deficiencies (specially vitamin B-12 deficiency), and exposure to some drugs (antibiotics, steroids, antivirals, anti-seizure drugs, chemotherapy).

However, a band of brown pigment in a single nail must be examined and investigated with caution, as melanonychia may be the presenting sign of melanoma (a malignant type of skin cancer). Some other signs that are red flags for the diagnosis of melanoma are: age >50 years old, a mix of colors within the nail lines, blurred borders, breadth more than 3 millimeters, melanonychia in a single nail (especially thumb, index finger or big toe), extension of pigment into nail fold (known as Hutchinson sign), family or personal history of melanoma.

In your case, I presume it is most likely caused by benign disorder, so you should not be worried, it doesn’t appear to be a melanoma. Nevertheless, you should see a Dermatologist so that a appropriate workup is carried out and a proper diagnosis and treatment is made.

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