# Acanthosis Nigricans > Acanthosis nigricans for NEET-PG Dermatology: insulin resistance types, malignant gastric carcinoma association, drugs and treatment in India. - Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/acanthosis-nigricans - Exam / course: NEET-PG · Subject: Dermatology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Acanthosis Nigricans", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/acanthosis-nigricans ## Direct answer Velvety, symmetric, hyperpigmented thickening of the flexures — neck, axillae, groins — is acanthosis nigricans, and in nine of ten Indian clinic patients it externalises insulin resistance, making it the skin's billboard for prediabetes, obesity, polycystic ovarian syndrome and type 2 diabetes. Beyond the common obesity-associated form live the endocrine variants (type A genetic insulin-receptor syndromes such as Rabson-Mendenhall, type B autoantibodies against the receptor in lupus), drug-induced disease (nicotinic acid, systemic steroids, oral contraceptives, growth hormone) and the malignant form — sudden-onset, rapidly spreading, intensely pruritic acanthosis with tripe palms in an older adult, pointing to gastric adenocarcinoma above all. Treatment is the cause: weight, glycaemia and metformin first, retinoids and lasers for cosmesis second. ## What you must remember - **Commonest cause:** obesity-associated insulin resistance; hyperinsulinaemia drives IGF-1 receptor stimulation on keratinocytes and fibroblasts — the mechanism sentence every viva wants. - **Clinical feel:** velvet to touch, dirty-looking hyperpigmentation with skin tags in the flexures; neck involvement brings patients in for "black neck" — the presenting complaint in Indian OPDs. - **Malignant red flags:** age above 40, onset over months, rapid spread, severe pruritus, thickened palms (tripe hands), mucosal and mucocutaneous involvement, weight loss — search the upper gastrointestinal tract, where gastric adenocarcinoma dominates. - **Endocrine classifications:** type A — young women with genetic insulin-receptor defects (Rabson-Mendenhall, Alstrom, Berardinelli-Seip lipodystrophy syndromes) with ovarian hyperandrogenism; type B — middle-aged women with autoantibodies to the insulin receptor, often with lupus or other autoimmune disease. - **Drug list:** nicotinic acid (the classic), glucocorticoids, combined oral contraceptives, growth hormone, insulin itself at injection sites, and stilboestrol historically. - **Workup of the common form:** fasting glucose, HbA1c, fasting insulin, lipid profile, and in women with hirsutism an androgen and ovarian ultrasound panel for PCOS. - **Separate entity:** acral acanthotic anomaly — benign darkening of the palms and dorsa of hands in older adults with no insulin resistance — commonly mistaken, examinable. - **Therapy reality:** no cream erases it; weight loss plus metformin softens it over months; keratolytics, topical retinoids and lasers offer cosmetic fringe benefit. ## Two patients, two utterly different meanings A 19-year-old engineering student presents with her mother, worried about a "black collar" that will not wash off; her body mass index is 31, the velvet plaques cover the nape and both axillae, and skin tags stud the fringes. The conversation pivots from cosmetic to cardiovascular: fasting glucose 112 mg/dL, HbA1c 6.2 per cent — prediabetes — fasting insulin high, lipids borderline. Her prescription is lifestyle plus metformin, with the explicit prediction that the neck will lighten only as insulin falls, over six to twelve months. Contrast a 58-year-old lean man with three months of explosive acanthosis, itching that keeps him awake, palms like tripe leather and 8 kg of weight loss. Here the flexures are a metastatic rumour of the stomach: upper gastrointestinal endoscopy is arranged as the "biopsy of the skin", gastric adenocarcinoma confirmed, and the dermatology team's job becomes tumour-directed therapy plus comfort, because the skin follows the cancer's curve. Same physical sign, opposite prognoses — that contrast is the entire teaching of this disease. ## Where candidates slip The reflex error is treating every acanthosis nigricans as benign obesity stigmata: the malignant form is the exam's deliberate trap, signalled by the words sudden, pruritic, rapidly progressive, acral or mucosal, and lean adult. The second slip is the mechanism: candidates say "pigment deposition" — histologically the darkness is hyperkeratosis and papillomatosis with only mild basal hyperpigmentation, which is why it feels velvet and returns after laser without metabolic correction. Third, the PCOS link: a young woman with acanthosis, hirsutism and irregular cycles should trigger an androgen and ultrasound workup, not just a dermatology prescription. And know acral acanthotic anomaly as the differential for isolated palm darkening, so a benign elderly finding is not escalated into a cancer hunt. ## Frequently asked questions ### Which malignancy is most associated with malignant acanthosis nigricans? Gastric adenocarcinoma, with other abdominal malignancies trailing; the skin may precede, accompany or follow tumour detection. ### What drives obesity-associated acanthosis nigricans? Hyperinsulinaemia crossing over to stimulate IGF-1 receptors on keratinocytes and dermal fibroblasts, producing hyperkeratosis and papillomatosis. ### Which features separate malignant from benign acanthosis? Sudden onset after age 40, rapid progression, severe pruritus, tripe palms, mucosal involvement and weight loss in a non-obese adult. ### Which drugs can induce acanthosis nigricans? Nicotinic acid classically, plus systemic corticosteroids, oral contraceptives, growth hormone and high-dose stilboestrol historically. ### What is acral acanthotic anomaly? A benign, acquired velvety darkening of the palms and dorsal hands in older adults, unlinked to insulin resistance or malignancy.