Acanthosis nigricans on axilla
|Classification and external resources|
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 armpits, groin, navel, forehead, and other areas.
- 1 Classification
- 2 Signs and symptoms
- 3 Causes
- 4 Pathophysiology
- 5 Diagnosis
- 6 Prognosis
- 7 Treatment
- 8 History
- 9 References
- 10 External links
- Benign This may include obesity-related, hereditary, and endocrine forms of acanthosis nigricans.
- Malignant. This may include forms that are associated with tumour products and insulin-like activity, or tumour necrosis factor.
An alternate classification system still used to describe acanthosis nigricans was proposed in 1994. 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.
Signs and symptoms
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.
- states with insulin resistance, such as diabetes mellitus and metabolic syndrome
- excess circulating androgens, particularly Cushing's disease, acromegaly, polycystic ovarian disease
- Addison's disease and hypothyroidism
- Rare diseases, including pinealoma, leprechaunism, lipotrophic diabetes, pineal hyperplasia syndrome, pituitary basophilism, ovarian hyperthecosis, stromal luteoma, ovarian dermoid cysts, Prader-Willi syndrome, and Alstrom syndrome.
Acanthosis nigricans associated with endocrine dysfunction is more insidious in its onset, is less widespread, and the patients are often concurrently obese.:676 This is also known as "Acanthosis nigricans type III",:506–7 and insulin resistance syndromes may be divided into Type A (HAIR-AN) and type B syndromes.:978
Insulin resistance and acanthosis nigricans
In young persons, AN is a visible marker which strongly suggests insulin resistance. Higher than normal insulin levels in the blood stream causes the growth of darkened skin over certain areas of the body. There is no skin treatment that will get rid of AN. Acanthosis Nigricans may lighten up and possibly go away by treating the root cause, Insulin Resistance but it can take months or years to do so.
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.:968 This is also known as "Pseudo-Acanthosis Nigricans", or "Type 3 Acanthosis Nigricans".:86
Acral Acanthotic Anomaly
Acral Acanthotic Anomaly refers to a variant of acanthosis nigricans limited to the elbows, knees, knuckles and dorsal surfaces of the feet, in the absence of any other findings, in otherwise healthy individuals. While the etiology remains unknown, its presence does not suggest a likelihood of malignancy.
Malignant acanthosis nigricans refers to acanthosis nigricans occurring as a paraneoplastic syndrome associated with a cancer. Malignant acanthosis nigricans is most-commonly associated with gastrointestinal adenocarcinomas, as well as genitourinary cancers such as those of the prostate, breast, and ovary. Other cancers, such as those of the lung, stomach, and lymphoma, are occasionally associated with acanthosis nigricans.:86
This form of acanthosis nigricans is more likely to involve mucous membranes (25-50% of cases) This variant is also known as Acanthosis nigricans type I:676 or 5.:86 Malignant acanthosis nigricans that may either precede (18%), accompany (60%), or follow (22%) the onset of an internal cancer.:506 Malignancy-associated acanthosis nigricans is usually rapid in onset and may be accompanied by skin tags, multiple seborrheic keratoses, or tripe palms.:676
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