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Authors: Vanessa Ngan, DermNet Staff Writer, 2004. Updated: Abdullah Haroon, Medical Student, Faculty of Medicine, University of Ottawa, Ontario, Canada. Copy edited by Gus Mitchell. December 2021
Acanthosis nigricans is a skin condition characterised by a velvety papillomatous overgrowth of the epidermis. Darkening and thickening (hyperkeratosis) of the skin occurs mainly in the flexural areas, particularly the axillae, groins, inframammary regions, and the neck.
Acanthosis nigricans is usually a sign of an underlying condition or disease, such as obesity or diabetes (benign). Its presence as a sign of internal malignancy is very rare.
The exact cause is still unclear, however it is predominantly linked to states of insulin resistance where obesity, diabetes, or metabolic disorders (eg, metabolic syndrome, polycystic ovary syndrome, generalised lipodystrophy) co-exist.
Insulin crosses the dermal-epidermal junction and, in high concentrations, can have growth-stimulating effects through its binding to type 1 insulin-like growth factor receptors (IGFRs) on keratinocytes. This stimulates the proliferation of these cells, leading to acanthosis nigricans.
Other rarer benign types include:
Rare malignant nigricans is:
The mainstay treatment is to manage the underlying disease. Patient education is also an important component.
Treatment of acanthosis nigricans lesions can also be undertaken for cosmetic reasons. Pharmacological treatment modalities can include:
Procedural modalities include:
Outcomes depend on the cause. If the underlying etiology can be addressed eg, weight loss, then the acanthosis nigricans can resolve. Obesity, metabolic syndrome, and diabetes have deleterious effects on overall morbidity and mortality. Hereditary acanthosis may stabilise and even regress spontaneously in some cases. Malignant acanthosis nigricans is associated with a poorer prognosis (average survival time is 2 years) with early mortality often due to advanced cancer.
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