The carpal tunnel is a narrow, tunnel-like structure in the wrist. The bottom and sides of this tunnel are formed by wrist (carpal) bones. The top of the tunnel is covered by a strong band of connective tissue called the transverse carpal ligament.
The median nerve travels from the forearm into the hand through this tunnel in the wrist. The median nerve controls feeling in the palm side of the thumb, index finger, and long fingers. The nerve also controls the muscles around the base of the thumb. The tendons that bend the fingers and thumb also travel through the carpal tunnel. These tendons are called flexor tendons.
Carpal tunnel syndrome occurs when the tissues surrounding the flexor tendons in the wrist swell and put pressure on the median nerve. These tissues are called the synovium. The synovium lubricates the tendons and makes it easier to move the fingers.
This swelling of the synovium narrows the confined space of the carpal tunnel, and over time, crowds the nerve.
Carpal tunnel syndrome is caused by pressure on the median nerve traveling through the carpal tunnel.
Many things contribute to the development of carpal tunnel syndrome:
- Heredity is the most important factor – carpal tunnels are smaller in some people, and this trait can run in families.
- Hand use over time can play a role.
- Hormonal changes related to pregnancy can play a role.
- Age — the disease occurs more frequently in older people.
- Medical conditions, including diabetes, rheumatoid arthritis, and thyroid gland imbalance can play a role.
- In most cases of carpal tunnel syndrome, there is no single cause.
The most common symptoms of carpal tunnel syndrome include:
- Numbness, tingling, and pain in the hand
- An electric shock-like feeling mostly in the thumb, index, and long fingers
- Strange sensations and pain traveling up the arm toward the shoulder
- Symptoms usually begin gradually, without a specific injury. In most people, symptoms are more severe on the thumb side of the hand.
Symptoms may occur at any time. Because many people sleep with their wrists curled, symptoms at night are common and may awaken you from sleep.
During the day, symptoms frequently occur when holding something, like a phone, or when reading or driving. Moving or shaking the hands often helps decrease symptoms.
Symptoms initially come and go, but over time they may become constant. A feeling of clumsiness or weakness can make delicate motions, like buttoning your shirt, difficult.
These feelings may cause you to drop things. If the condition is very severe, muscles at the base of the thumb may become visibly wasted.
To determine whether you have carpal tunnel syndrome, your doctor will discuss your symptoms and medical history.
He or she will also examine your hand and perform a number of physical tests, such as:
- Checking for weakness in the muscles around the base of your thumb
- Bending and holding your wrists in positions to test for numbness or tingling in your hands
- Pressing down on the median nerve in the wrist to see if it causes any numbness or tingling
- Tapping along the median nerve in the wrist to see whether tingling is produced in any of the fingers
- Testing the feeling in your fingers by lightly touching them when your eyes are closed
Electrical testing of median nerve function is often done to help confirm the diagnosis and clarify the best treatment option in your case.
If you have limited wrist motion, your doctor may order x-rays of your wrist.