What Is Carpal Tunnel Syndrome?

The carpal tunnel is a narrow channel about 1 inch long between the wrist and the hand.

This anatomic tunnel is formed by the bones on the back of the wrist and is covered by a thick band of connective tissue on the front (palm side) of the wrist, and contains tendons and the median nerve.

Carpal tunnel syndrome occurs when the median nerve, which runs from the forearm to the palm of the hand, is compressed by swelling of other tissues within the carpal tunnel or by narrowing of the carpal tunnel. The median nerve provides sensation to the thumb, the index finger, the middle finger, and half of the ring finger and is responsible for movement of all of the fingers and the wrist.

Common symptoms of carpal tunnel syndrome are a gradual onset of numbness or tingling in the thumb and the index, middle, and half of the ring finger, and thumb weakness. Carpal tunnel syndrome can occur in one or both hands, often produces symptoms at night, and can affect either the nondominant hand or the dominant hand first or more severely. If left untreated, patients can develop permanent numbness in these areas of the hand and a decrease in size (atrophy) of the thumb muscle with permanent weakness.

Carpal tunnel syndrome is a common condition that occurs more frequently in individuals who are female, middle aged, or pregnant or have medical conditions such as diabetes, obesity, and hypothyroidism. Certain jobs are associated with higher rates of carpal tunnel syndrome, including those involving repetitive wrist and fingers movements (such as computer use for more than 4 hours per day) or operation of heavy machinery that applies strong vibrations to the hands or requires forceful hand gripping.

The diagnosis of carpal tunnel syndrome is generally based on characteristic symptoms and physical examination findings, including decreased sensation in the thumb and the index, middle, and half of the ring finger, and thumb weakness. Nerve conduction studies and electromyography, which are specialized tests that measure nerve and muscle function, may be performed to confirm the diagnosis of carpal tunnel syndrome. Ultrasound imaging is also a useful noninvasive test to diagnose carpal tunnel syndrome.

Initial treatment of carpal tunnel syndrome involves avoidance of symptom-provoking activities and use of a wrist splint at night. In addition, specialized range-of-motion wrist exercises, often prescribed by a certified hand specialist, can improve symptoms. Steroid injection into the affected area may result in modest relief of symptoms; however, the benefit generally lasts only 1 to 3 months, and there is a small risk of worsening of nerve compression, unintentional injection into the median nerve, or damage to tendons within the carpal tunnel.

Patients with carpal tunnel syndrome who have symptoms that do not improve after 6 weeks of nonoperative treatment or who have symptoms of constant numbness or atrophy of the thumb muscle should be evaluated by a hand surgeon. In most appropriately selected patients, surgery improves symptoms of carpal tunnel syndrome. Potential rare complications of carpal tunnel surgery include infection, development of a painful scar, or injury to the median nerve.

Published Online: June 28, 2022. doi:10.1001/jama.2022.10522

Conflict of Interest Disclosures: None reported.

Source: Currie KB, Tadisina KK, Mackinnon SE. Common hand conditions: a review. JAMA. Published June 28, 2022. doi:10.1001/jama.2022.8481