- Asymmetric velvety thickening and hyperpigmentation of the skin, chiefly on the neck, axilla, groins, and other body folds.
- May be hyperkeratotic and associated with skin tags.
- A cutaneous marker related to heredity, obesity, endocrine disorders (particularly diabetes), drug administration, and malignancy.
- Insidious onset; in malignancy, rapid.
Type 1: Hereditary Benign AN
No associated endocrine disorder.
Endocrine disorders associated with insulin resistance: insulin-resistant type II diabetes mellitus, hyperandrogenic states, acromegaly/gigantism, Cushing disease, hypogonadal syndromes with insulin resistance, Addison disease, hypothyroidism.
Associated with obesity; more common in patients with darker pigmentation. Common in metabolic syndrome. Obesity produces insulin resistance.
Nicotinic acid in high dosage, stilbestrol in young males, glucocorticoid therapy, diethylstilbestrol/oral contraceptive, growth hormone therapy.
Paraneoplastic, usually adenocarcinoma of gastrointestinal or genitourinary tract; less commonly, lymphoma (see Section 18).
Type 1: during childhood or puberty; other types dependent on associated conditions.
Etiology and Pathogenesis
Dependent on associated disorder. In a subset of women with hyperandrogenism and insulin intolerance and AN, loss-of-function mutation in the insulin receptor or anti-insulin receptor antibodies can be found (types A and B). It is postulated that excess growth factor stimulation in the skin leads to proliferation of keratinocytes and fibroblasts. In hyperinsulinemia AN, excess insulin binding to insulin–like growth factor 1 receptor and fibroblast growth factor receptor has also been implicated. In malignancy-associated AN, transforming growth factor β released from tumor cells may stimulate keratinocyte proliferation via epidermal growth factor receptors.
Insidious onset; first visible change is darkening of pigmentation.
All types of AN: Darkening of pigmentation, skin appears dirty (Fig. 5-1). As skin thickens, appears velvety; skin lines accentuated; surface becomes rugose, mammillated. Type 3: velvety patch on inner, upper thigh at site of chafing; often has many skin tags in body folds and neck. Type 5: hyperkeratosis and hyperpigmentation more pronounced (see Fig. 18-16). Hyperkeratosis of palms/soles, with accentuation of papillary markings: “Tripe hands” (see Fig. 18-18), involvement of oral mucosa and vermilion border of lips (see Fig. 18-17).
Acanthosis nigricans Velvety, dark-brown to gray thickening of the skin of the armpit with prominent skin folds and feathered edges in a 30-year-old obese woman from the Middle East. There were similar changes on the neck, the antecubital ...
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