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. Signs and symptoms
Acanthosis nigricans may present with thickened, velvety, relatively darker areas of skin on the neck, armpit and in skin folds. Causes
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 syndrome, insulin-resistant diabetes or Cushings disease. Type I – familial
Familial acanthosis: 86  may arise as a result of an autosomal dominant trait, presenting at birth or developing during childhood. : 506 : 676

Type II – endocrine
Endocrine syndromes associated with acanthosis nigricans: 506–7  can develop in many conditions, particularly:: 978  : 86 
starts with insulin resistance, such as diabetes mellitus and metabolic syndrome
excess circulating androgens, particularly Cushings disease, acromegaly, polycystic ovary syndrome
Addisons 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.Acanthosis nigricans associated with endocrine dysfunction is more insidious in its onset, is less widespread, and the patients are often concurrently obese.
Nevus lipomatosus (cutaneous) superficialis (NLS or NLCS, also known as "Nevus lipomatosis of Hoffman and Zurhelle") is characterized by soft, yellowish papules or cerebriform plaques, usually of the buttock or thigh, less often of the ear or scalp, with a wrinkled rather than warty surface. : 625  It is usually congenital
in origin or appears within the first three decades.A pedunculated lipofibroma is a solitary variant of nevus lipomatosus superficialis. It usually appears in adult life, and usually on the axilla, knee, ear, arm, scalp and the lower trunk. In both multiple and solitary variants, the histopathology shows variable amounts of mature lipocytes within the dermis. Occasionally, there is an excessive fibrocollagenous tissue proliferation. The main differential diagnoses are acrochordon, seborrheic keratosis, intradermal melanocytic nevi, neurofibromas, verrucae and fibroepithelioma of Pinkus. See also
Skin lesion
List of cutaneous conditions


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