Acanthosis nigricans is dark, thick, velvety skin in body folds such as the neck, armpits and groin. It is most often a sign of insulin resistance linked to obesity, prediabetes, type 2 diabetes or polycystic ovary syndrome, and rarely a sign of internal cancer.
Key symptoms
- Dark, velvety patches on the neck, armpits or groin
- Skin that looks dirty but does not wash off
- Skin tags and mild itching
- Signs of the cause: thirst, irregular periods, excess hair
What you find on exam
- Location and texture of the patches
- BMI, waist size and blood pressure
- Signs of polycystic ovary syndrome: excess hair, acne
- Check the palms and mouth, which are unusual sites
Tests
- HbA1c or fasting glucose
- Lipid panel
- Testosterone if periods are irregular or there is excess hair
- Search for cancer if onset is sudden and widespread in an adult without obesity
Treatment basics
- Treat the cause: weight loss, exercise and diet
- Metformin for insulin resistance or prediabetes when indicated
- Topical retinoid such as tretinoin or a urea cream to improve appearance
- Stop causative drugs such as niacin or systemic steroids when possible
Red flags
- Sudden, fast-spreading patches in an adult without obesity
- Involvement of the mouth or palms
- Unexplained weight loss, early satiety or abdominal pain
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.