About Carpal Tunnel Syndrome

Carpal tunnel syndrome is a peripheral nerve compression syndrome in which the median nerve, which is responsible for sensation in the thumb, index finger, middle finger, and the thumb-side half of the ring finger, as well as part of the thumb’s motor function, is compressed at the wrist. This results in numbness, pain, decreased sensation, swelling, and weakness in the hand and fingers.

The wrist is one of the parts of the body with the greatest range of motion. Tendons of muscles involved in hand movement, sensory nerves responsible for hand sensation, motor nerves involved in movement, and blood vessels necessary for blood supply to the hand extend from the arm to the hand through the wrist. On the back of the hand side, the tendons of muscles, sensory nerves, motor nerves, and blood vessels pass through the wrist while spreading out widely. On the palm side, these structures pass through the wrist while gathering toward the center of the palm, and this is the narrowest area, so the structures become crowded at the wrist.

When these structures pass through the wrist on the palm side, there is a membrane covering them from above, called the transverse carpal ligament (horizontal carpal ligament, carpal ligament, transverse wrist ligament). The tendons of the muscles and the nerves lie beneath this ligament. The space enclosed by this ligament and the surrounding tissues is called the carpal tunnel, and the tendons and nerves involved in hand movement are located inside it. Carpal tunnel syndrome occurs because pressure within the carpal tunnel increases and compresses the median nerve, one of the structures passing through this tunnel. However, sensitivity to pressure differs from person to person, so even if the pressure in the carpal tunnel is high, carpal tunnel syndrome may not develop, and in some cases it may develop even if the pressure is not very high.

Unlike tendons, nerves are not hard tissue and are soft, so they are easily damaged by compression. When the median nerve is compressed within the carpal tunnel, either the space of the carpal tunnel becomes narrower or the contents within the space expand, creating the effect of a relatively narrower carpal tunnel.

The carpal tunnel becomes smaller when the wrist is bent too far toward the back of the hand or too far toward the palm. Also, if the transverse carpal ligament becomes thickened, the space of the carpal tunnel underneath it becomes narrower, and the median nerve is pressed within the tunnel. When the wrist is bent too far toward the palm, some of the structures that were in the palm are pushed toward the wrist, increasing the volume of the contents within the carpal tunnel and making compression of the median nerve more pronounced.

When muscle tendons pass through the carpal tunnel, each tendon is surrounded by a thin membrane. This membrane helps each tendon slide smoothly within the carpal tunnel when the fingers are clenched or extended, but if the tendons are used too much and become irritated or inflamed, the membrane surrounding the tendons thickens and swells, increasing the volume of the structures within the carpal tunnel. As a result, the space in the carpal tunnel becomes relatively narrower, and the median nerve may be compressed.

In general, many people think of hand numbness as a circulation problem, but when the hand is actually numb, it is often due to a peripheral nerve disorder, and carpal tunnel syndrome is especially often the cause. In particular, if your hand becomes numb at night so that you cannot sleep deeply or you wake up while sleeping, it is worth considering the possibility of carpal tunnel syndrome.

Carpal tunnel syndrome is a relatively common disease, occurring in about 1 to 2 out of every 1,000 people. It mainly appears in adults over the age of 30 and occurs more often in women than in men, especially middle-aged women. In terms of occupation, it is common among workers who are exposed to a lot of vibration, people whose jobs involve repeated forceful wrist-bending motions, office workers who spend a lot of time working at a computer with the wrist in a fixed position, and people who use their hands repeatedly at high speed. In students, it may also occur if they have a habit of gripping a pen tightly while writing.

In most cases, it occurs without any particular preexisting disease, but it can also occur after a wrist fracture due to malunion, arthritis, tumors that develop within the carpal tunnel (such as ganglion cysts), or systemic causes, especially in patients with diabetes or chronic kidney failure. Common associated conditions include rheumatoid arthritis, tendinitis, amyloidosis, hypothyroidism, diabetes, acromegaly, and bone and joint deformities, but in most patients the exact cause is unknown, and it is thought to be related to excessive repetitive use of the hands. Some believe it may be caused by hormonal changes in women during menopause or by aging. In addition, in people with diabetes, because diabetes itself affects the nerves, hand numbness appears more often and more severely even if there is only slight swelling around the wrist. Also, in pregnant women, carpal tunnel syndrome may appear temporarily and then improve after delivery, and the cause is thought to be pregnancy-related edema.

So far, I have explained carpal tunnel syndrome.

In the next part, we will look at the symptoms and diagnosis of carpal tunnel syndrome.

Source: Korea Disease Control and Prevention Agency National Health Information Portal