Pathology Science: Why is there a black line on my nail?

"Doctor, why is there a black stripe on my nail? Is it the legendary melanoma?"

Before answering this question, let's take a look at the nails. Nails are located at the end of fingers (toes), and they are responsible for protecting the distal finger (toe) and the nail bed. The hard component exposed on the surface is the nail plate, which is actually a connective tissue, and its main component is keratin. This is why we ordinary people often say that the hardness of nails can reflect a person's nutritional status; the nail bed that is tightly attached to the nail plate below is similar to the epidermis in structure, but contains abundant blood vessels and nerve endings, which is why bleeding and pain are obvious after the nail is injured; the root of the nail is the nail matrix, which is covered and protected by the nail epithelium. Its function is to use newly generated nail cells to push old cells outward and promote the renewal of nails.

There are often three reasons for the appearance of black lines on the nails:

1. Subungual bleeding

When the nail is injured, the capillaries in the nail bed will rupture. After the blood flows out, it cannot be discharged in time due to the obstruction of the nail plate, which will cause blood to accumulate between the nail and the nail bed, forming a black-red patch with clear boundaries, and sometimes in the shape of lines. Subungual bleeding can occur on the fingernails or toenails, and is most common on the thumb and big toe. Most of them are located at the top of the nail, and there is slight pain when pressing. The dried blood clots can be slowly pushed out of the nail bed to heal as the nail plate grows, and generally no special treatment is required. The causes are mostly trauma, squeezing, thrombocytopenia, etc. Wearing ill-fitting shoes can also cause subungual bleeding.

2. Nail matrix nevus

The nail matrix nevus is actually a type of nevus, also called the black line of the nail or the longitudinal black nail. It is a pigmented nevus that occurs on the nail matrix. The tissue classification is mostly junctional nevus (common nevus are divided into junctional nevus, intradermal nevus, and mixed nevus. The probability of malignant transformation of junctional nevus is higher than the other two types). Melanin overflows to the nail plate and moves forward as the nail plate grows. Unlike subungual bleeding, the nail matrix nevus occurs from the root of the nail (toe) and grows toward the distal end of the nail (toe). It appears to the naked eye as a longitudinal, straight dark brown line on the nail (toe). The color depth varies from person to person, and the width is mostly <3mm, with clear boundaries. The nail matrix nevus can occur at any age, without pain or itching. Once it appears, it persists and a few may become malignant. Therefore, once a black line appears on the nail (toe), you still have to go to the dermatology department for treatment, do a dermoscopy first, and if necessary, perform a surgical biopsy and send it to pathology for further diagnosis.

3. Melanoma

Melanoma is a highly malignant tumor derived from melanocytes. Patients with nail melanoma may also have some black lines on their nails or black patches under the nails. Lines that are wider than 3mm, irregular in shape, blurred at the edges, color changes, and even deformation and bulging of the nails are all warning signs that should be paid close attention. If the above symptoms occur, you should go to a regular hospital in time for treatment. After a biopsy and surgical pathology diagnosis, surgical treatment should be performed as soon as possible.