Acanthosis nigricans

Specialty: Skin.

• velvet hyperpigmentation of folds
• pigmentary keratosis of flexures

Why it occurs

• Peripheral insulin resistance (hyperinsulinemia that stimulates insulin-like growth factor type 1 [IGF-1] receptors in keratinocytes and fibroblasts)
• Long-term obesity (most common cause of epidermal metabolic overstimulation)
• Endocrinopathies such as polycystic ovary syndrome (PCOS) or acromegaly
• Gastric adenocarcinoma or other visceral neoplasms (malignant acanthosis nigricans, with abrupt onset and severe extension)
• Drugs such as the systemic use of glucocorticoids, high-dose oral contraceptives or niacin.

Initial workup

Measurement of basal blood glucose and serum insulin to calculate the HOMA-IR index, glycosylated hemoglobin (HbA1c), complete lipid profile. In suspected malignancy: upper gastrointestinal endoscopy, computed tomography (CT) of the abdomen and pelvis, and tumor markers such as CEA and CA 19-9.

Standard management

• Metformin — insulin-sensitizing drug that corrects underlying hyperinsulinism; usual 500 to 1000 mg every 12 hours
• Tretinoin cream 0.05% — topical retinoid that normalizes keratinocyte proliferation
• 6% salicylic acid ointment — keratolytic agent designed to reduce the thickness of hyperkeratotic plaques
• Urea 20% (keratolytic and moisturizing agent to improve the texture of the affected skin).