Acanthosis nigricans (AN) is a rare congenital or acquired secondary skin disease characterized by darkening (hyperpigmentation) and thickening (hyperkeratosis) of the skin. The folds are symmetrically involved: plaques with the morphological characteristics of AN are found in the armpit (axilla), groin and back of the neck. It is subdivided into benign (“pseudoacanthosis nigricans”) and malignant AN.We present a case of a 43-year-old woman with AN with localized symmetrically pigmented plaques with a papillomatous surface in the axils, nape, back of the feet. The patient has clinical manifestations of grade III obesity (BMI > 40 kg/m2) and insulin-resistant diabetes with a duration of more than 10 years. Hypothyroidism, acromegaly, polycystic ovary and Cushing’s disease are excluded. Screening for visceral neoplasia was performed. The family survey did not reveal any manifestation of AN among the relatives.AN is most likely caused by factors that stimulate the proliferation of keratinocytes in the epidermis and fibroblasts in the dermis. In the benign form of AN, such a factor is probably insulin or insulin-like growth factor (IGF), which stimulates the growth of epidermal cells. Tyrosine kinase receptors (epidermal growth factor receptor or fibroblast growth factor receptor) also play a role. At high concentrations, insulin exerts a potent proliferative effect by binding with high affinity to IGF-1 receptors. In addition, free IGF-1 levels may be elevated in obese patients with hyperinsulinemia, leading to accelerated cell growth and differentiation. The case presented is illustrative of a rare dermatosis, which may be congenital or a paraneoplastic dermadrome. Read the full article here.