Carpal tunnel syndrome: Compression and irritation of the median nerve as it passes under the transverse carpal ligament in the wrist. Abbreviated CTS. CTS can be due to trauma from repetitive work, such as that of retail checkers and cashiers, assembly line workers, meat packers, typists, writers, and accountants. Other factors that can cause CTS include obesity, pregnancy, hypothyroidism, arthritis, and diabetes. The symptoms of CTS include numbness, tingling, a 'pins and needles' feeling especially at night in the hand, particularly in the thumb, index, and middle fingers. CTS can also cause wrist pain, weakness in the grip, and a feeling of hand incoordination. In some cases the pain seems to migrate up from the wrist and into the arm, shoulder, and neck. The diagnosis is suspected based on symptoms, supported by signs on physical examination, and confirmed by nerve conduction testing. Treatment depends on the severity of symptoms and the underlying cause. Early CTS is usually treated by modification of activities, a removable wrist brace, exercises and/or manipulation (massage), and anti-inflammatory medicines. If detected early, CTS is reversible. If numbness and pain continue in the wrist and hand, cortisone injection into the carpal tunnel can help. Surgery is used only when other treatments have failed. In advanced CTS, particularly if there is profound weakness and muscle atrophy (wasting), surgery is done to avoid permanent nerve damage.