Acanthosis nigricans

Acanthosis nigricans is a brown to black, poorly defined, velvety hyperpigmentation of the skin, usually present in the posterior and lateral folds of the neck, the axilla, groin, umbilicus, and other areas.

Causes

This occurs due to insulin spillover (from excessive production due to obesity or insulin resistance) into the skin which results in abnormal growth being observed.

The most common cause would be insulin resistance, usually from type 2 diabetes mellitus.

Other causes are familial, obesity, drug-induced, malignant (gastric cancer), idiopathic, and Polycystic ovary syndrome. In the context of a malignant disease, Acanthosis nigricans is a paraneoplastic syndrome and is then commonly referred to as Acanthosis nigricans maligna. Involvement of mucous membranes is rare and suggests a coexisting malignant condition. It typically occurs in individuals younger than age 40, may be genetically inherited, and is associated with obesity or endocrinopathies, such as hypothyroidism or hyperthyroidism, acromegaly, polycystic ovary disease, insulin-resistant diabetes, or Cushing's disease. When seen in individuals older than age 40, this disorder is commonly associated with an internal malignancy, usually adenocarcinoma, and most commonly of the GI tract or uterus; less commonly of the lung, prostate, breast, or ovary. Acanthosis nigricans of the oral mucosa or tongue is highly suggestive of a neoplasm, especially of the GI tract.

Signs and tests

Physicians can usually diagnose acanthosis nigricans by simply looking at a patient's skin. A skin biopsy may be needed in unusual cases. If no clear cause of acanthosis nigricans is obvious, it may be necessary to search for one. Blood tests, an endoscopy, or x-rays may be required to eliminate the possibility of diabetes or cancer as the cause.

Acanthosis nigricans is characterized by a dark, slightly raised, velvetlike eruption of the flexural areas. Most often seen in the axillae, it can also occur in the inguinal area, on the sides of the neck, in the abdominal area, and even in the mouth. There are several classifications of causation and type of lesions. The most common scenario is the development of lesions in obese persons, those with adult-onset diabetes mellitus, or those with a strong family history of diabetes mellitus. The acanthosis is thought to be representative of insulin resistance. Some cases may follow a hereditable pattern, with or without diabetes. Acanthosis nigricans may be a manifestation of internal malignancy, including solid tumors and lymphoma, or it can develop as the result of drug ingestion. The diagnosis is most often clinical, but a skin biopsy can be performed when the diagnosis is unclear. At times superficial fungal or yeast infections can imitate acanthosis nigricans. Treatment is difficult unless the underlying condition is removed. In patients with rapid onset and a negative family history, malignancy must be considered as a cause.

Treatment

People with acanthosis nigricans should be screened for diabetes and, although rare, cancer. Controlling blood glucose levels through exercise and diet often improves symptoms.

Prognosis

Acanthosis nigricans often fades if the underlying cause can be determined and treated appropriately.