Carpal tunnel syndrome is caused by pressure on the median nerve.

The median nerve runs from your forearm through a passageway in your wrist (carpal tunnel) to your hand. It provides sensation to the palm side of your thumb and fingers, except the little finger. It also provides nerve signals to move the muscles around the base of your thumb (motor function).
Anything that squeezes or irritates the median nerve in the carpal tunnel space may lead to carpal tunnel syndrome.
Chiropractors can accurately diagnose carpal tunnel syndrome because they have special expertise in the nerve entrapment syndromes. Treatment may include manipulation of your wrist or elbow, or relieving pressure on the nerve.