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Carpal tunnel syndrome is a nerve entrapment disorder that results from compression of the median nerve which winds its way through the wrist through a narrow passageway called the carpal tunnel. This compression typically causes pain, numbness, and tingling in the thumb, index finger, middle finger, and the thumb side of the ring finger, which are the areas of skin innervated by the median nerve. Now taking a cross-section of the wrist, we’ll see a bony arch known as a carpal arch on the dorsal side of the hand which forms the floor of the carpal tunnel, and a sheath of connective tissue called the flexor retinaculum or transverse carpal ligament, which is on the palmer side of the hand forms the roof of the carpal tunnel.

Also, there are nine flexor tendons, which go to the fingers and thumb, as well as one nerve—the median nerve—which travels down the forearm and goes through the carpal tunnel. The skin of the hand served by the median nerve includes the thumb, the index finger, and the middle finger, as well as half of the ring finger that’s on the thumb side. The other side of the ring finger and pinky are served by the ulnar nerve, and the back of the hand’s served by the radial nerve, only the median nerve goes through the carpal tunnel. Carpal tunnel syndrome is caused by compression of the median nerve, and that typically happens as a result of inflammation of the nearby tendons and tissues, which creates local edema or swelling which increases the amount of fluid in a very tight space, and essentially puts pressure on the median nerve.

Initially, that pressure can cause a dull ache or discomfort in any of the areas of the hand that is innervated by the median nerve. Eventually, this discomfort can lead to sharp, pins-and-needles-like pain, called paresthesia, which can extend up the forearm. People might also have muscle weakness which can cause clumsiness with tasks like holding small objects, turning doorknobs and keys, or fine motor tasks like buttoning up a shirt. In severe situations, the thenar muscles at the base of the thumb can start to waste away. This happens because those muscles are innervated by the recurrent branch of the median nerve which arises from the median nerve after it passes through the carpal tunnel.

Basically, in a nutshell, any structure innervated by the median nerve downstream of the point of compression can be affected. Interestingly, a superficial sensory branch of the median nerve, called the palmar branch, provides sensation to the central base of the palm. Because this nerve branches upstream or proximal to the carpal tunnel and travels superficially to it, this nerve is not affected by carpal tunnel syndrome and this is also why there is no loss of sensation in the central palm of the hand. Typically in carpal tunnel syndrome, both hands are affected because usually there is a repetitive stress injury like typing which causes inflammation in both wrists. This also explains why symptoms of carpal tunnel syndrome tend to be worse at night, after a day of use. Other risk factors of carpal tunnel syndrome include obesity or pregnancy, as well as having underlying conditions like rheumatoid arthritis, where there’s joint inflammation from an autoimmune process leads to the compression of the median nerve.

Diagnosis of carpal tunnel syndrome can be made based on electrophysiological testing, description or symptoms, as well as physical tests. For example, Phalen’s maneuver, where you flex the wrists are far as possible and then hold that position for a minute, results in numbness in the areas of the hand innervated by the median nerve in people with carpal tunnel syndrome. Another physical test, Tinel’s sign, is performed by tapping the transverse carpal ligament which reproduces the symptoms of tingling or feelings of pins and needles in areas of the hand served by the median nerve. Finally, there’s Durkan’s test, which is another way to elicit carpal tunnel symptoms, but this time by manually compressing the carpal tunnel with the thumb for 30 seconds.

One major form of treatment is behavior modification, many of which are associated with hand positions while typing which is a common cause of the problem. Changes like keeping the axis of the hands parallel to each other and the table, using a computer mouse instead of a trackpad, and wearing wrist supports and splints while typing, can all be super helpful. Physical therapy in the form of stretching and isometric exercises can also help relieve symptoms. In more serious cases it might be treated non-surgically by splinting or corticosteroid injection, but the definitive management often requires surgical division of the transverse carpal ligament to help open up the carpal tunnel and relieve the pressure.

Alright as a quick recap: carpal tunnel syndrome is a condition most often characterized by numbness and tingling in the hand caused by a compressed median nerve in the wrist, and if necessary can be surgically treated by the release of the transverse carpal ligament which forms the roof of the carpal tunnel.

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