Carpal tunnel syndrome explained

What carpal tunnel syndrome is

The carpal tunnel is a narrow passage on the palm side of the wrist, formed by the wrist bones and a tough band of tissue across the top. Running through this tunnel are the tendons that bend the fingers and one important nerve, called the median nerve, which supplies feeling to the thumb, index, middle and part of the ring finger and helps move some of the thumb muscles. Carpal tunnel syndrome happens when this nerve becomes squeezed within the tunnel, usually because the space inside becomes crowded or the lining swells. The pressure disturbs the nerve's signals, causing the typical tingling, numbness and, over time, weakness. It is one of the most common nerve compression problems and affects women more often than men. Although it can be uncomfortable and annoying, it is usually treatable and not dangerous.

The symptoms it causes

The classic symptoms of carpal tunnel syndrome are tingling, pins and needles, and numbness in the thumb, index and middle fingers and half of the ring finger, following the area supplied by the squeezed nerve. Symptoms are often worse at night and can wake people from sleep, and they may be brought on by activities that bend the wrist for a while, such as holding a phone, driving or reading. Many people find that shaking or flicking the hand brings relief. As the condition progresses, the hand may feel clumsy or weak, making it harder to grip, do up buttons or hold small objects, and in longer-standing cases the fleshy muscle at the base of the thumb can waste away. Symptoms usually build up gradually and may affect one or both hands. The little finger is typically spared, which helps distinguish it from other nerve problems.

What causes it and who gets it

Often no single cause is found, but several things can crowd the carpal tunnel or make the nerve more vulnerable. It is more common in women and tends to occur in middle age. It can be linked to pregnancy, when fluid retention increases pressure in the tunnel, and often settles after the baby is born. Conditions such as an underactive thyroid, diabetes, rheumatoid arthritis and being overweight can increase the risk, as can a previous wrist fracture that narrows the tunnel. Work or hobbies involving repeated forceful gripping or strong vibration may contribute in some people, though the role of ordinary keyboard use is debated. Carpal tunnel syndrome can also run in families, as some people naturally have a narrower tunnel. Identifying any contributing factor, such as a thyroid problem, can be part of managing the condition.

How it is diagnosed

Carpal tunnel syndrome is often recognised from the typical story of tingling and numbness in the thumb-side fingers, worse at night and relieved by shaking the hand. A doctor will ask about the symptoms and examine the hand, checking sensation, the strength of the thumb muscles and whether the base of the thumb has wasted. They may perform simple bedside tests, such as tapping over the nerve at the wrist or holding the wrist bent, to see if these reproduce the tingling. In many cases the diagnosis can be made from the history and examination alone. Where the picture is unclear, the symptoms are severe, or surgery is being considered, a nerve conduction test may be arranged to measure how well the nerve is working and confirm where it is being squeezed. Blood tests are sometimes done to look for contributing conditions.

How it is treated

Treatment depends on how troublesome the symptoms are and how long they have been present. Mild cases often improve with simple measures, such as wearing a wrist splint, particularly at night, to keep the wrist in a neutral position, and adjusting activities that trigger symptoms. Managing any underlying condition, such as a thyroid problem, can help, and carpal tunnel linked to pregnancy often eases after delivery. If symptoms persist, a steroid injection into the wrist can reduce swelling around the nerve and relieve symptoms for a time. When symptoms are severe, do not respond to other measures, or there is nerve damage with numbness or muscle wasting, a small operation called carpal tunnel release can be done to cut the band over the tunnel and take the pressure off the nerve, which is usually very effective. Your clinician will advise which approach suits your situation.