Acanthosis nigricans is a general term that describes a symptom -- a blackening of the skin -- not a specific skin condition. Although acanthosis nigricans is not dangerous by itself, the underlying condition causing it may be, so it is important to consult a doctor if the symptom appears. Various factors and diseases can lead to acanthosis nigricans, and treatment and prognosis depend on the initial cause.
Acanthosis nigricans is a discoloration, or hyperpigmentation, of the skin, often coupled with a thickening that results in a velvety texture. The symptom may be benign or malignant. Malignant acanthosis nigricans is caused by cancerous cells in the body, while the benign forms have a variety of causes. The condition can affect people of all ages and genders.
Changing skin color and texture is the only significant sign of acanthosis nigricans. In most cases, the skin develops a black-ish color, but it can also appear greyish brown. Skin tags are common, and the affected skin is usually rough and itchy. Although the condition can appear anywhere on the body, skin folds, including the underarms, groin, back of the neck, and the genital area, are the most common locations.
The most common cause of acanthosis nigricans is obesity. As many as 20 percent of adults who are overweight develop the symptom, and it can also affect children. Many clinicians now believe the condition is linked to insulin resistance. The cells of people with insulin resistance do not respond normally to the hormone, and some researchers believe the insulin finds its way into the skin, producing the symptoms. Insulin resistance is connected to obesity and type 2 diabetes.
Numerous syndromes are associated with acanthosis nigricans. Many of these are hormonal, much like insulin resistance, and include:
Some medications that affect hormones may also be the culprit behind acanthosis nigricans. People taking human growth hormone, corticosteroids, and oral contraceptives may experience the symptoms.
In some cases, acanthosis nigricans appears in otherwise healthy people, with no apparent underlying cause. Sometimes this is hereditary. When the condition runs in the family, it may develop from birth, but more often appears in childhood or later. Some non-hormonal medications may trigger symptoms, including high doses of niacin and some bodybuilding supplements. Occasionally, the condition develops spontaneously. Doctors refer to this phenomenon as an acral acanthotic anomaly.
Certain types of cancer cause malignant acanthosis nigricans. In 90 percent of cases of this type, the underlying cancer is a tumor of the gut, most significantly stomach cancer. Sometimes, the sign appears in the mouth, on the lips and tongue. Though malignant causes are rare, the development of acanthosis nigricans indicates an advanced tumor, so it is important that doctors rule out the possibility of cancer.
A few conditions have similar symptoms to acanthosis nigricans, including Becker nevus and Gougerot-Carteaud syndrome. To ensure the correct diagnosis, doctors will ask for patient history, including a family history of the condition and details of the symptoms. They may also perform a skin biopsy. Once the doctor confirms the diagnosis, they can investigate the cause, which may involve blood tests to determine hormone levels and imaging scans if the physician suspects cancer.
When the cause is identified, treatment almost always helps the discoloration fade. If obesity is the cause, losing weight can diminish the appearance of acanthosis nigricans. Removing cancerous tumors can also reverse the symptom, as can ceasing suspect medications. Prescription creams can help soften and lighten skin during the recovery period, and topical antibiotics and antibacterial soaps can help if the lesions begin to smell. Laser treatments can also reduce the thickness of skin. People should refrain from scratching itchy skin, as this can make the condition worse.
People with benign acanthosis nigricans generally have good outcomes if they make lifestyle changes or treat the underlying cause of the symptoms. Those with hereditary conditions may have long-lasting symptoms and treatment generally focuses on improving cosmetic appearance. By contrast, the prognosis for people with malignant acanthosis nigricans is poor, as the cancers that cause it are usually aggressive and advanced.
The risk factors for acanthosis nigricans depend on the underlying cause. This includes obesity and a genetic predisposition for certain diseases, such as PCOS. People of African, Caribbean, Hispanic, or Native American descent are more likely to develop spontaneous acanthosis nigricans. Malignant types are more common in people over 40, but can still develop at any age, including childhood.
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