Acanthosis Nigricans
Basics
Basics

Basics
Description
Description
Description
- Acanthosis nigricans (AN) is a benign dermatosis characterized by velvety, hyperpigmented, hyperkeratotic plaques, which
- Are usually symmetric
- Most often occur on the posterior neck, flexural and intertriginous surfaces (axilla, elbow, inframammary areas, groin and anogenital regions), and sometimes in mucocutaneous areas
- Are most often asymptomatic but may cause pruritus
- Typically a sign of hyperinsulinemia and insulin resistance but can be a marker of malignancy
- Individuals with AN are at risk of developing metabolic syndrome.
- Etiologies include obesity, insulin resistance, genetic syndromes, familial AN, malignant AN, and drug reactions (1).
Epidemiology
Epidemiology
Epidemiology
- AN is more common between the ages of 11 and 40 years and in those with body mass index (BMI) ≥30.
- It is more common in individuals with diabetes or risk factors for diabetes.
- It may be a useful indicator of risk of diabetes mellitus (2) and subclinical atherosclerosis (3).
Prevalence
- Prevalence of AN in unselected populations varies from 7% to 74% according to age, race, frequency of type, degree of obesity, and concomitant endocrinopathies (2).
- It is more prevalent in Hispanic, African American, and Native American individuals compared to white or Asian individuals (1).
- In a study of 89 African Americans with AN, there was a 21.3% frequency of DM2 (2).
Etiology and Pathophysiology
Etiology and Pathophysiology
Etiology and Pathophysiology
- Obesity induced (pseudo-AN) and insulin resistance (2)
- Are the most common etiologies of AN
- More prevalent in individuals with BMI >30. It is weight dependent and may regress with weight loss.
- Higher prevalence of AN in individuals with more risk factors for diabetes and those with type 2 diabetes
- Other endocrinopathies associated with AN include polycystic ovarian syndrome (PCOS), acromegaly, and Cushing syndrome; thyroid diseases; hirsutism; and Addison disease.
- Syndromic AN (1)
- Genetic disorders characterized by insulin resistance can also present with AN. Examples include Down syndrome, leprechaunism, congenital generalized lipodystrophy, and familial partial lipodystrophy.
- Familial AN (1)
- Autosomal dominant mutation of the fibroblast growth factor receptor 3 gene
- Lesions are usually seen in early childhood.
- Malignant AN (1)
- A rare cause of AN characterized by
- Sudden onset, rapid progression, and more extensive lesions
- Presents in atypical locations such as in the mucosa, palms, and soles
- It usually presents in older adults who are often not obese.
- 90–95% are associated with abdominal cavity adenocarcinomas.
- May also present with other cutaneous disorders representing internal malignancy such as Leser-Trélat sign (sudden onset of multiple seborrheic keratosis) or tripe palms (ridged velvety lesions of the palms)
- Drug-induced AN (1)
- A rare cause that can be seen with drugs that promote hyperinsulinemia such as systemic glucocorticoids, insulin, oral contraceptives (OCPs), niacin, testosterone, and protease inhibitors
- Lesions usually regress after discontinuation of these drugs.
Genetics
High levels of insulin stimulate epidermal keratocytes and dermal fibroblasts via insulin-like growth factor receptors (IGF-1). The keratocyte proliferation leads to skin changes like papillomatosis and hyperkeratosis (4).
Risk Factors
Risk Factors
Risk Factors
- Obesity (3)
- Insulin resistance (3)
- Race and ethnicity (3)
- Family history of DM2 (3)
General Prevention
General Prevention
General Prevention
Encourage diet and exercise to all age groups to reduce likelihood of insulin resistance syndrome.
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