Amelanotic Melanoma and Subungual Melanomaby Kevin Berman, M.D. Health Professional
When we talk about melanoma, most people picture an irregular, dark, large mole that has changed over time, and indeed, these characteristics are often symptoms of melanoma. Today I want to talk about two variants of melanoma that are harder to diagnose than those mentioned above.
A melanoma that does not have dark pigment is termed an "amelanotic melanoma" and these account for less than 5% of all melanoma diagnoses. While they may appear to have irregular borders and asymmetry, these are hard to diagnose because they tend to be fleshy or reddish in color. Because they lack the characteristic dark color of melanoma, they are often overlooked by patients and physicians and are diagnosed only after they have grown large in size or behin to bleed or cause pain and itching. They can be confused with other types of skin cancer, or just a normal mole that appears inflamed.
At the time of diagnosis, these lesions tend to be nodular and thick, which is associated with a worse prognosis (compared to the more common superficial spreading melanoma). It is not clear why the melanocytes of these cancers do not produce pigment. Once diagnosed, the treatment is similar to any other melanoma, including surgery and possibly chemotherapy.
Another type of melanoma that is often overlooked is subungual melanoma, which is melanoma under the fingernails or toenails. This type of melanoma can appear as a nodule, often appearing like the amelanotic melanoma described above. In this case, it is often destructive to the nail plate and can cause pain. More commonly, subungual melanoma appears as a dark longitudinal band running the length of the nail. It can be several millimeters wide or can affect a much wider width of the nail. This melanoma is often overlooked because it is very common for people with dark colored skin to have darkly pigmented longitudinal streaks (termed benign melanonychia) in the nail. These are not dangerous.
Also, trauma to the nail (such as getting a finger caught in a car door) can cause a collection of blood under the nail that looks like a dangerous mole. Fungal and bacterial infections of the nail can also cause dark streaks. In this case, a person will often assume the dark streak is just blood or fungus and not seek treatment. A dark streak that appears after the age of 50 is concerning, as is any widening of an existing dark streak.
A very concerning finding is called "Hutchinson's sign", which is darkening of the cuticle usually associated with melanoma. The biopsy of these lesions is not easy and is much more involved than the usual "shave biopsy" of a suspicious lesion elsewhere on the body. In order to get a biopsy of the nail bed and nail matrix, the skin around the cuticle is usually cut and pulled back and a small piece of tissue is removed. The area is then closed with stitches. Treatment of subungual melanoma is primarily surgical, with complete excision being the goal.
I hope this brief discussion sheds some light on two types of melanoma that are often overlooked. Fortunately, these variants are rare but be aware to alert your dermatologist if you have any growths that you are concerned about.