Melanonychia is a condition characterized by the brown or black discoloration of a nail. This pigmentation typically appears as a stripe that extends lengthwise from the base of the nail to its tip. It can affect fingernails or toenails. This nail discoloration is a result of melanin, the pigment responsible for skin color, being deposited into the nail plate.
Understanding Melanonychia
Melanonychia commonly manifests as a longitudinal brown or black band on the nail plate, often referred to as longitudinal melanonychia or melanonychia striata. The appearance of these bands can vary in width, color intensity, and the number of bands present on a single nail. While it most frequently presents as a lengthwise stripe, the discoloration can also be diffuse, covering the entire nail, or transverse, appearing as a band across the width of the nail. This pigmentation occurs when melanocytes, the pigment-producing cells in the nail matrix, deposit melanin into the growing nail plate. As the nail grows, this melanin becomes incorporated, leading to the visible streak.
Common Causes of Melanonychia
The appearance of melanonychia stems from two primary processes: melanocytic activation or melanocytic hyperplasia. Melanocytic activation involves increased melanin production by normal melanocytes, while melanocytic hyperplasia signifies an increase in pigment cells. Many causes are benign.
Racial melanonychia, also known as physiologic melanonychia, is a common benign cause, especially in individuals with darker skin tones. Trauma to the nail matrix, such as repetitive pressure or a direct injury, can also trigger melanocytes to produce more melanin, leading to discoloration. Certain fungal infections, like onychomycosis, can produce melanin and deposit it into the nail plate, resulting in a dark streak. Some medications, particularly chemotherapy drugs, and systemic conditions such as Addison’s disease or Laugier-Hunziker syndrome, can also cause melanonychia.
A more concerning cause is subungual melanoma, a rare form of skin cancer that develops under the nail. This malignant condition involves an increase in cancerous melanocytes. Subungual melanoma is serious because it can spread if not detected early. Distinguishing between benign and malignant causes often requires professional medical evaluation.
When to Seek Medical Advice
Any new or changing dark streak on a nail warrants medical evaluation. A healthcare professional, typically a dermatologist, can assess the characteristics of the streak and perform necessary diagnostic steps. While many cases are benign, early detection of subungual melanoma is important for effective treatment.
Signs indicating a higher risk for subungual melanoma and necessitating prompt medical attention include changes in the streak’s appearance. These warning signs can be remembered using the “ABCDEF” rule: Asymmetry (the streak is uneven in color or shape), Border irregularity (the edges are blurred or notched), Color variation (different shades of brown, black, or even red/blue within the streak), Diameter or Darkness (the streak is wider than 3 millimeters or becoming darker), Evolving (the streak is changing in size, shape, or color), and Extension of pigment to the nail fold (the color spreads onto the skin around the nail). A healthcare provider will often perform a dermatoscopic examination to closely inspect the discolored area. If melanoma is suspected, a biopsy, which involves taking a small tissue sample from the nail matrix or nail bed, is often performed to confirm the diagnosis.
Management and Outlook
The management of melanonychia depends on its underlying cause. If the melanonychia is diagnosed as benign, such as due to trauma or racial variation, specific treatment may not be necessary. Regular monitoring might be recommended to ensure no concerning changes occur over time.
If the discoloration is linked to a medication, discontinuing or adjusting the drug under a doctor’s supervision may lead to the streak fading or resolving. Similarly, if an infection is the cause, appropriate antifungal or antibiotic treatment can resolve the pigmentation. For cases diagnosed as subungual melanoma, surgical removal of the affected nail unit and surrounding tissue is the primary treatment. In some situations, further therapies, such as radiation or immunotherapy, might be considered if the cancer has spread. The outlook for melanonychia is generally good when the cause is benign, but early diagnosis and intervention are important for malignant forms like subungual melanoma.