Acanthosis Nigricans: Skin Sign of Insulin Resistance & Other Conditions

Acanthosis nigricans (AN) presents as velvety, hyperpigmented, thickened plaques in intertriginous zones (axillae, neck, groin). It is a cutaneous marker—not a primary skin disease.

Associated Conditions

• Insulin resistance / hyperinsulinemia: Most common (obesity, type 2 diabetes, PCOS, metabolic syndrome).
• Malignancy (paraneoplastic): Gastric adenocarcinoma (classic), lung, uterine, lymphoma — abrupt onset, extensive, mucosal involvement.
• Endocrine: Acromegaly, Cushing’s, hypothyroidism, Addison’s.
• Drug-induced: OCPs, high-dose niacin, corticosteroids, protease inhibitors.
• Genetic: Benign familial AN (autosomal dominant).

Clinical Approach

1. Identify context: obesity/IR vs. sudden/severe/mucosal → malignancy workup.
2. Screen: fasting glucose, HbA1c, lipids, consider age-appropriate cancer screening.
3. Treat underlying cause: weight loss, insulin sensitizers (metformin) often improve AN.
4. Topical: retinoids, ammonium lactate, calcipotriol for cosmetic concern.

AN is a visible clue to systemic pathology—don’t treat skin in isolation.