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What is True about acanthosis nigricans and explain in detail?
ACANTHOSIS NIGRICANS Classification * Hereditary AN * HAIR-AN syndrome:  Several endocrine disorders associated. HyperAndrogenism, Insulin Resistance and Acanthosis Nigricans. * Benign acquired AN:  Obesity associated. Earlier called pseudo AN. * Drug-induced AN:  Nicotinic acid, stilbestrol, coicosteroids, oral contraceptives. * Malignant AN:  Adenocarcinoma of stomach and genitourinary tract. Clinical Features Morphology:- Begins as hyperpigmentation and area appears  diy. Gradually, skin thickens and becomes velvety.  Surface of skin appears rugose and mammillated. The edge of lesion feathered. Sites of predilection:- Neck, axillae, and groins frequently. Other flexures (antecubital and popliteal fossae, face sometimes; submammary folds, wrists less frequently. Associations:- Depends on type of AN: * HAIR- AN syndrome: Several endocrine disorders associated. Insulin-resistant diabetes mellitus, hyperandrogenic states, Cushing's syndrome * Benign acquired AN: Skin tags in the major flexures. * Malignant AN:  Several associations: Tripe palms, Mucosal involvement, Severe itching. Investigations Rule out:- Underlying endocrinopathies. Underlying malignancies. Treatment:- Retinoic acid (0.025%) topically, response often  unsatisfactory. Ref:- Neena khanna; pg num:- 37,38