Acanthosis nigricans-insulin resistance-muscle cramps-acral enlargement syndrome is not a recognized medical condition. Acanthosis nigricans is a skin condition characterized by dark, velvety patches on the skin, usually in the armpits, neck, and groin. Insulin resistance is a condition in which the body does not respond properly to the hormone insulin, leading to high blood sugar levels. Muscle cramps are sudden, involuntary contractions of a muscle or group of muscles. Acral enlargement is an enlargement of the hands and feet.