On physical examination, acanthosis nigricans is observed. What is the most likely diagnosis?

• A. Diabetes
• B. Hypertension
• C. Allergy
• D. Osteoarthritis

Answer: (A)

Acanthosis nigricans signals insulin resistance, which is most commonly tied to type 2 diabetes or a prediabetic state. The excess insulin circulating in the body stimulates skin cells—particularly in friction-prone areas like the neck, armpits, and groin—causing the characteristic dark, velvety patches. So, when you see these skin changes on examination, diabetes (or an insulin-resistant condition) is the most likely diagnosis. The other options—hypertension, allergy, and osteoarthritis—do not typically present with acanthosis nigricans. (Note: in some older adults, acanthosis nigricans can hint at an occult malignancy, but the association with diabetes is the most common and likely explanation in a typical exam scenario.)