Acanthosis nigricans

Acanthosis nigricans is a medical sign characterised by 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. It is associated with endocrine dysfunction, especially insulin resistance and hyperinsulinaemia, as seen in diabetes mellitus. This activates the insulin-like growth factor receptors, which leads to proliferation of keratinocytes, fibroblasts and other cells in the skin. Activation of other growth factor receptors such as fibroblast growth factor receptors or epidermal growth factor receptor can also be responsible. Acanthosis nigricans appears as dark brown-black, poorly defined, velvety patches of skin, typically affecting the face, neck, underarms, genitals, groin, elbows, knees, anus, umbilicus and nasal crease. It typically occurs in individuals younger than age 40, is associated with insulin resistance, Type 2 diabetes, obesity or endocrinopathies, such as hypothyroidism, acromegaly, polycystic ovary syndrome or Cushing's disease, and may be genetically inherited. Familial acanthosis may arise as a result of an autosomal dominant trait, presenting at birth or developing during childhood. File:Familial acanthosis nigricans.jpg File:Familial acanthosis nigricans2.jpg File:Familial acanthosis nigricans3.jpg File:Familial acanthosis nigricans4.jpg File:Familial acanthosis nigricans5.jpg Endocrine syndromes associated with acanthosis nigricans can develop in many conditions, particularly: starts with insulin resistance, such as diabetes mellitus and metabolic syndrome excess circulating androgens, particularly Cushing's disease, acromegaly, polycystic ovary syndrome Addison's disease and hypothyroidism Rare diseases, including pinealoma, leprechaunism, lipoatrophic diabetes, pineal hyperplasia syndrome, pituitary basophilism, ovarian hyperthecosis, stromal luteoma, ovarian dermoid cysts, Prader-Willi syndrome, and Alström syndrome.