Carpal tunnel syndrome is a common condition that causes pain, numbness, and tingling in the hand and arm. The condition occurs when one of the major nerves to the hand — the median nerve — is squeezed or compressed as it travels through the wrist.
In most patients, carpal tunnel syndrome gets worse over time, so early diagnosis and treatment are important. Early on, symptoms can often be relieved with simple measures like wearing a wrist splint or avoiding certain activities.
If pressure on the median nerve continues, however, it can lead to nerve damage and worsening symptoms. To prevent permanent damage, surgery to take pressure off the median nerve may be recommended for some patients.
The carpal tunnel is a narrow passageway in the wrist, about an inch wide. The floor and sides of the tunnel are formed by small wrist bones called carpal bones.
The roof of the tunnel is a strong band of connective tissue called the transverse carpal ligament. Because these boundaries are very rigid, the carpal tunnel has little capacity to “stretch” or increase in size.
The median nerve is one of the main nerves in the hand. It originates as a group of nerve roots in the neck. These roots come together to form a single nerve in the arm. The median nerve goes down the arm and forearm, passes through the carpal tunnel at the wrist, and goes into the hand. The nerve provides feeling in the thumb and index, middle, and ring fingers. The nerve also controls the muscles around the base of the thumb.
The nine 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 tunnel becomes narrowed or when tissues surrounding the flexor tendons swell, putting pressure on the median nerve. These tissues are called the synovium. Normally, the synovium lubricates the tendons, making it easier to move your fingers.
When the synovium swells, it takes up space in the carpal tunnel and, over time, crowds the nerve. This abnormal pressure on the nerve can result in pain, numbness, tingling, and weakness in the hand.
Most cases of carpal tunnel syndrome are caused by a combination of factors. Studies show that women and older people are more likely to develop the condition.
Other risk factors for carpal tunnel syndrome include:
Symptoms of carpal tunnel syndrome may include:
In most cases, the symptoms of carpal tunnel syndrome begin gradually—without a specific injury. Many patients find that their symptoms come and go at first. However, as the condition worsens, symptoms may occur more frequently or may persist for longer periods of time.
Night-time symptoms are very common. Because many people sleep with their wrists bent, symptoms may awaken you from sleep. During the day, symptoms often occur when holding something for a prolonged period of time with the wrist bent forward or backward, such as when using a phone, driving, or reading a book.
Many patients find that moving or shaking their hands helps relieve their symptoms.
During your evaluation, your doctor will talk to you about your general health and medical history and will ask about your symptoms.
He or she will carefully examine your hand and wrist and perform a number of physical tests. During these tests, your doctor will:
Electrophysiological tests. These tests will help your doctor measure how well your median nerve is working and help determine whether there is too much pressure on the nerve. The tests will also help your doctor determine whether you have another nerve condition, such as neuropathy, or other sites of nerve compression that might be contributing to your symptoms.
Electrophysiological tests may include:
Ultrasound. An ultrasound uses high-frequency sound waves to help create pictures of bone and tissue. Your doctor may recommend an ultrasound of your wrist to evaluate the median nerve for signs of compression.
X-rays. X-rays provide images of dense structures, such as bone. If you have limited wrist motion or wrist pain, your doctor may order x-rays to exclude other causes for your symptoms, such as arthritis, ligament injury, or a fracture.
Magnetic resonance imaging (MRI) scans. These studies provide better images of the body’s soft tissues. Your doctor may order an MRI to help determine other causes for your symptoms or to look for abnormal tissues that could be impacting the median nerve. An MRI can also help your doctor determine if there are problems with the nerve itself—such as scarring from an injury or tumor.