Melanonychia is a brown or black discoloration of nails that can be benign or a sign of cancer. It can be caused by medical conditions, medications, trauma, or infections. Dark-skinned individuals are more prone to it, and it can also be a side effect of chemotherapy or radiation. A biopsy may be necessary to diagnose malignancy.
Melanonychia refers to a band of brown or black discoloration of the fingernails or toenails. The condition can be benign or indicative of a type of cancer. Some noncancerous medical conditions can cause the abnormality, along with some medications. Health care providers usually require a thorough medical history and physical evaluation to rule out possible contributing factors.
The discoloration usually develops lengthwise, from the cuticle to the tip of the nail. The cuticle may or may not be included in the coloring. The bands or streaks associated with this condition may appear as a single line or cover the nail completely. The index finger, thumb, and big toe are the most common sites of the affliction, but multiple fingers can be involved.
The band can appear as a solid color or transition from one shade of brown to another. Sometimes fine, regular or irregular lines appear. The coloring line can have parallel edges or be irregular. Symptoms may also appear as purplish-blue to brown dots or spots of dried blood under the nail.
Abnormally large deposits of melanin often occur in the nails of people who have dark skin. Studies indicate that 77% of individuals of African descent suffer from melanonychia. The condition can also occur in people of Asian descent 10% to 20% of the time. Only 1% of people with Caucasian ancestry experience this skin condition.
Trauma to the fingers or toes commonly produces nail discoloration, and bacterial and fungal infections can also cause melanonychia. Many medical conditions, including Addison’s disease and psoriasis, cause nail discoloration. The rare syndrome known as Langier-Hunziker typically causes oral hyperpigmentation, and individuals who have this acquired disorder may also develop excessive discoloration under the fingernails or toenails.
Side effects associated with chemotherapy, radiation, and warfarin can cause melanonychia. Other drugs that could contribute to the abnormal pigmentation are hydroxyurea, minocycline and zidovudine. The discoloration usually goes away once treatment is finished or the causative medications are no longer needed.
Melanonychia can also indicate a serious type of skin cancer. If left undiagnosed and untreated, the malignancy can metastasize to the bone, central nervous system, and organs of the body. Doctors can perform a biopsy to identify possible malignant cells associated with melanoma.
Dermatologists who suspect malignancy can obtain samples by shaving a thin layer of tissue. Doctors can also access tissue by biopsy or surgical excision. A positive malignant diagnosis generally requires that the affected area undergo surgical removal.
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