Acanthosis nigricans

Acanthosis nigricans is a brown to black, poorly defined, velvety hyperpigmentation of the skin. It is usually found in body folds,[1] such as the posterior and lateral folds of the neck, the armpits, groin, navel, forehead, and other areas.

Acanthosis nigricans is conventionally divided into benign and malignant forms.,[2][3] although may be divided into syndromes according to cause.[4]:506

  • Benign This may include obesity-related, hereditary, and endocrine forms of acanthosis nigricans.[2]
  • Malignant. This may include forms that are associated with tumour products and insulin-like activity, or tumour necrosis factor [2]

An alternate classification system still used to describe acanthosis nigricans was proposed in 1994 by dermatologist Schwartz. This classification system delineates acanthosis nigricans syndromes according to their associated syndromes, including benign and malignant forms, forms associated with obesity and drugs, acral acanthosis nigricans, unilateral acanthosis nigricans, and mixed and syndromic forms

Acanthosis nigricans may present with thickened, relatively darker areas of skin on the neck, armpit and in skin folds.[2]


It typically occurs in individuals younger than age 40, may be genetically inherited, and is associated with obesity or endocrinopathies, such as hypothyroidism, acromegaly, polycystic ovary disease, insulin-resistant diabetes, or Cushing's disease.


Endocrine syndromes associated with acanthosis nigricans can develop in a large amount of conditions, particularly:[2]:978 [7]:86

Acanthosis nigricans associated with endocrine dysfunction is more insidious in its onset, is less widespread, and the patients are often concurrently obese.[8]:676 This is also known as "Acanthosis nigricans type III",[4]:506–7 and insulin resistance syndromes may be divided into Type A (HAIR-AN) and type B syndromes.[2]:978


The majority of cases of acanthosis nigricans are associated with obesity and otherwise idiopathic. This is likely because of insulin resistance, and more likely to occur in darker-skinned persons.[2]:968 This is also known as "Pseudo-Acanthosis Nigricans", or "Type 3 Acanthosis Nigricans".[7]:86

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