The symptoms of carpal tunnel syndrome (CTS) are caused by squashing (compression) of the median nerve at the wrist.
The median nerve is responsible for two main functions:
- carrying physical sensations such as your sense of touch from your hand to your brain
- carrying nerve signals from your brain to your hand, controlling movement
Any pressure on the median nerve can disrupt the nerve signals, affecting your sense of touch and hand movements.
The median nerve can become compressed if the tissues inside the tunnel become swollen or the tunnel narrows over time.
In most cases, it's not known what causes the median nerve to become compressed, although a number of things increase the risk of developing CTS.
- family history
- certain health conditions, such as diabetes, an underactive thyroid gland or rheumatoid arthritis
- certain injuries to the wrist
- certain activities
These risk factors are outlined below.
Research has shown there's a genetic link to CTS. This means you may have an increased risk of developing it if other members of your family have the condition or have had it in the past.
About one in four people with CTS have a close relative, such as a parent, brother or sister, who also has the condition. It's not fully understood how and why the condition is passed on through families.
Certain health conditions appear to increase your risk of developing CTS.
- diabetes – a chronic (long-term) condition caused by having too much sugar (glucose) in the blood
- any kind of arthritis – a condition where the joints become painful and inflamed
- hypothyroidism – an underactive thyroid gland
- obesity in young people
- some drugs used to treat breast cancer – such as exemestane (Aromasin)
CTS can also develop when a person has an abnormal wrist structure, such as an unusually narrow carpal tunnel. It can also be a result of cysts, growths or swellings in the carpal tunnel.
CTS is common during pregnancy, although the exact cause isn't known. Many cases resolve after the baby is born.
It's not known whether women who have carpal tunnel syndrome during pregnancy are at greater risk of developing the condition in later life.
CTS is also common in women around the time of the menopause.
CTS can sometimes occur after a hand injury, such as a sprain, fracture or crush injury. This is because the swelling places pressure on the median nerve.
Also, these types of injuries can change the natural shape of the bones and ligaments in the hand, leading to increased pressure on the median nerve.
Certain activities may trigger the development of carpal tunnel syndrome. These tend to involve strenuous grip, bending the wrist repetitively (flexion) and exposure to vibration.
- playing a musical instrument
- assembly packing
- work that involves manual labour
- work with vibrating tools, such as chainsaws
Further research into the link between work-related hand use and CTS is required to determine how important these types of activities are in causing the condition.
Although typing is often thought of as a possible cause of carpal tunnel syndrome, CTS is actually less common in people who type all day than those who carry out more strenuous activities.