Acanthosis nigricans is a brown to black, poorly defined, velvety hyperpigmentation of the skin. It is usually found in body folds, such as the posterior and lateral folds of the neck, the axilla, groin, umbilicus, forehead, and other areas.
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.
The most common cause of Acanthosis nigricans is insulin resistance, which leads to increased circulating insulin levels. Insulin spillover into the skin results in its abnormal growth, and the stimulation of color producing cells (melanocytes).
The most common cause of insulin resistance is type 2 diabetes mellitus. Other causes of insulin resistance include obesity, 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.
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.
Other causes of Acanthosis nigricans are familial, drug-induced and idiopathic.
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.
People with acanthosis nigricans should be screened for diabetes and, although rare, cancer. Controlling blood glucose levels through exercise and diet often improves symptoms.
Acanthosis nigricans often fades if the underlying cause can be determined and treated appropriately.