Acanthosis nigricans (AN) is a skin condition marked by dark patches, especially in the folds of the skin. It is most common in obese people and in those who have or may develop type 2 diabetes (condition characterized by the body’s inability to use the hormone insulin effectively).

There are two major types of AN:

• Benign acanthosis nigricans. This type can be divided into three categories:
  
  
• Endocrine. Most commonly affiliated with type 2 diabetes or insulin resistance.
  
  
• Drug induced. Often results from the use of oral steroids, birth control pills or nicotinic acid (a cholesterol lowering agent).
  
  
• Idiopathic. The cause is unknown.

• Malignant acanthosis nigricans. This type is rare and associated with cancerous internal tumors (abnormal growths).

Scientists are not certain what causes AN. It appears to be due to overstimulation of skin cells of the epidermis. AN can affect people of all ages and both genders. People with darker skin are more susceptible to AN than people with lighter skin.

AN does not pose a health threat to patients and is primarily a cosmetic problem of the epidermis. Certain people may develop itchiness (pruritus) associated with the skin plaques. However, the underlying condition that causes AN may be relatively harmless (e.g., use of certain medications) or potentially life-threatening (e.g., aggressive cancers), and may require medical treatment.

A physical examination and medical history are the primary methods of diagnosing AN. In some cases, blood tests or biopsies may also be helpful in determining a diagnosis.

Losing weight and making other lifestyle changes to reduce the levels of insulin in the blood may improve most cases of AN. In other cases, stopping the use of the medication that triggered the condition or treating an underlying tumor may be the key to reversing AN.

Acanthosis nigricans (AN) is a skin condition associated with dark, gray-brown to black velvety plaques. These occur especially in the folds of the skin, such as the back or side of the neck, armpits, abdomen, breasts and groin. The plaques can also occur elsewhere on the body, including on the knuckles, elbows, knees, scalp, eyelids, face and palms. The skin changes usually appear gradually over months to years. "Acanthosis” means thickening of the skin. “Nigricans" refers to the dark discoloration.

There are two major types of AN:

• Benign acanthosis nigricans. This type can be divided into three categories:
  
  
• Endocrine. Most commonly affiliated with type 2 diabetes (a condition characterized by the body’s inability to use the hormone insulin effectively) or insulin resistance, a condition that can lead to diabetes.
  
  
• Drug induced. Often results from the use of oral steroids, birth control pills or nicotinic acid (a cholesterol-lowering agent).
  
  
• Idiopathic. The cause is unknown.
  
  
• Malignant acanthosis nigricans. This type is rare and associated with cancerous internal tumors (abnormal growths). It is usually fast growing and has a sudden onset. It is often secondary to gastrointestinal or genitourinary cancers. It may also be associated with lymphomas.

Benign AN is harmless and is primarily a cosmetic concern that affects many people with diabetes. Almost 75 percent of children with type 2 diabetes have benign acanthosis nigricans, according to the American Diabetes Association (ADA). The prevalence of AN is expected to rise along with the soaring rate of childhood obesity and people with type 2 diabetes. Some people with AN inherit the condition, which tends to appear during childhood before plaques stabilize or improve over time.

Reports of the association between AN and insulin resistance and diabetes in children have prompted calls by some parents and diabetes groups to screen schoolchildren for AN. The U.S. Centers for Disease Control and Prevention (CDC) responded to the request, but denied the applicability of widespread school-based screening for AN as a reliable method of identifying children at risk for type 2 diabetes.

People who have symptoms of AN are urged to consult a physician. Although there is no particular treatment for AN, the skin discoloration often fades when the underlying condition that causes it is successfully treated.

Scientists are not certain what causes acanthosis nigricans (AN). It appears to be due to overstimulation of the epidermal skin cells. AN is often the result of obesity caused by insulin resistance. This is a condition in which the body makes insulin but no longer uses it properly. Insulin is the hormone that regulates blood sugar (glucose) levels. Insulin resistance causes a buildup of insulin in the blood (hyperinsulinemia).

The excess insulin may activate insulin receptors in the skin and cause the abnormal growth. Excess insulin can indicate or lead to several serious health conditions. It is also a major factor in the development of diabetes (condition characterized by the body’s inability to produce or use the hormone insulin effectively).

Other factors are also believed to cause some cases of AN by overexciting skin cells. These include:

• Endocrine disorders. Conditions that affect the endocrine system, a group of glands that use hormones to help control reproduction, metabolism, growth and development. Examples of these disorders include polycystic ovary syndrome and Cushing’s syndrome.
  
  
• Heredity. AN can be inherited as an autosomal recessive or dominant trait, meaning that just one parent has to have an abnormal gene in order for a child to inherit the disease.
  
  
• Cancer. The skin cell overgrowth is stimulated by a tumor (abnormal growth) or as a response to a tumor. Examples of such cancers include lymphoma and cancers of the gastrointestinal or genitourinary tracts. It tends to affect people who are middle-aged, even if they are not obese.
  
  
• Medications. Certain medications can trigger AN. These include human growth hormone, nicotinic acid (a drug to lower high cholesterol levels), birth control pills, steroids, and pituitary and other drugs for endocrine system conditions.

AN affects people of all ages and genders. People with darker skin are more susceptible to AN than people with light-colored skin.

Acanthosis nigricans (AN) is characterized by dark, gray-brown to black plaques. These skin changes usually appear very gradually, sometimes over a period of months or years. Often the discolored areas thicken and become raised plaques. Small noncancerous outgrowths called acrochordons, or skin tags, may develop. Sometimes, itching (pruritus) is present.

AN occurs most often in obese people in the folds of skin, such as the neck, inner elbows, armpits, abdomen and groin. Sometimes it is seen over the joints or on the scalp, eyelids, mouth, palms of the hands or soles of the feet. Patients may complain that their skin looks dirty and cannot be scrubbed clean.

AN is sometimes confused with psoriasis. However, the plaques of AN are not red and inflamed like those caused by psoriasis.

The U.S. Centers for Disease Control and Prevention (CDC) has noted that there is no gold standard for diagnosing acanthosis nigricans (AN). In diagnosing this condition, a physician will perform a complete physical examination. AN may be apparent on visual inspection.

In addition, the physician will compile a thorough medical history, including a family history. People who have relatives with type 2 diabetes (condition characterized by the body’s inability to use the hormone insulin effectively) tend to be more prone to AN.

Other methods a physician may use to examine a patient for AN include:

• Blood tests. An elevated fasting blood insulin (hormone that regulates blood sugar) level suggests the hyperinsulinemia (accumulation of insulin) that is usually present in AN. Results of blood glucose tests are often normal in people with insulin resistance.
  
  
• Biopsy. Sometimes a small tissue sample may be taken and examined under a microscope to rule out other skin conditions.

When AN is diagnosed, the possibility of prediabetes or diabetes should be investigated.

Acanthosis nigricans (AN) is usually due to an underlying disorder that must be treated. It is difficult to treat the skin plaques associated with AN without addressing their cause.

Cases of AN that are caused by insulin (hormone that regulates blood sugar) resistance may be improved or resolved by controlling diabetes (condition characterized by the body’s inability to use insulin effectively) risk factors to lower the amount of unused insulin the body. Certain diets can help reduce a person’s level of insulin, which often causes AN symptoms to fade rapidly.

Weight loss can help reduce AN associated with obesity, whereas treatment of underlying tumors (abnormal growths) can help reverse AN associated with cancer. AN that results from the use of medications will usually disappear when the patient ceases using the medication. The inherited or familial form of AN tends to resolve over time.

Topical medications including antibiotics, retinoids and keratolytics (abrasives) have been tried, with varying degrees of success. Some patients may benefit from prescription creams and lotions that help lighten the skin color in the affected areas. Dermabrasion or laser therapy may also be performed to reduce the skin thickness in certain areas.

The prognosis for most types of AN is usually good. However, the prognosis for people with malignant AN is often poor, as the cancer is often very aggressive.

Preparing questions in advance can help patients to have more meaningful discussions with healthcare professionals regarding their condition. Patients may wish to ask their doctor the following questions related to acanthosis nigricans (AN):

1. What are the first signs that I may have AN?
   
   
2. How will you diagnose AN?
   
   
3. What is the likely cause of AN?
   
   
4. If I have AN, should I be tested for diabetes?
   
   
5. Are the skin plaques likely to worsen in appearance?
   
   
6. What are my treatment options for AN? What are the pros and cons of these treatments?
   
   
7. What are my treatment options for the condition causing AN?
   
   
8. If a medication causes AN, are there other drugs I can use instead?
   
   
9. Am I candidate for laser or dermabrasion therapy?
   
   
10. What is my long-term prognosis?