Acanthosis nigricans

Associate Editor-In-Chief:

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.

Common 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.

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.

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.