Carpal tunnel syndrome (CTS) is a medical condition due to compression of the median nerve as it travels through the wrist at the carpal tunnel. The main symptoms are pain, numbness and tingling in the thumb, index finger, middle finger, and the thumb side of the ring finger. Symptoms typically start gradually and during the night. Pain may extend up the arm. Weak grip strength may occur, and after a long period of time, the muscles at the base of the thumb may waste away. In more than half of the cases, both hands are affected.