The symptoms of carpal tunnel syndrome (CTS) are caused by compression (squashing) of the median nerve at the wrist. The median nerve is responsible for two main functions:
- relaying physical sensations – such as your sense of touch from your hand to your brain
- relaying nerve signals – from your brain to your hand, allowing you to move your hand and fingers
The compression of the median nerve can disrupt the nerve signals, affecting your sense of touch and hand movements. The median nerve can become compressed if the tendons that run through the carpal tunnel are swollen and inflamed.
Risk factors
In most cases, it is not known what causes the median nerve to become swollen and inflamed. Cases of CTS where the cause is unknown are called idiopathic. Although the exact cause of CTS is often unknown, a number of risk factors for the condition have been identified. These include:
- family history
- certain health conditions
- pregnancy
- certain injuries
- certain activities
These risk factors are outlined below.
Family history
Research has shown that there may be a genetic link to CTS. This means you may have an increased risk of developing CTS 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 is not fully understood exactly how and why the condition is passed on through families.
Health conditions
Certain health conditions appear to increase your risk of developing CTS. These include:
- type 1 diabetes and type 2 diabetes – a chronic (long-term) condition that is caused by having too much sugar (glucose) in the blood
- rheumatoid arthritis – a condition where the joints become painful and inflamed as a result of the immune system attacking the body
- gout – a common type of arthritis that causes pain and swelling in one or more joints
- hypothyroidism – an underactive thyroid gland
- obesity – particularly in young people
- oedema – an excess build-up of fluid in the body’s tissue
Less commonly, CTS occurs when a person has an abnormal wrist structure, such as an unusually narrow carpal tunnel, or as a result of cysts, growths or swellings in the tendons or blood vessels that pass through the carpal tunnel.
Pregnancy
CTS is common during pregnancy. This is due to fluid retention (oedema), where a build-up of fluid that often occurs in the hands and arms (as well as in the legs, ankles and feet) causes swelling in these areas. Oedema can occur during pregnancy, resulting in pressure being placed on the median nerve.
Injuries
CTS can sometimes occur following a hand injury. Injuries, such as sprains (a stretched, twisted or torn ligament), a fracture (a break or crack in the bone) and crush injuries (where an external force causes an injury to a body part) can cause swelling and place pressure on the median nerve.
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 and the symptoms of CTS.
Certain activities
It has been suggested that certain activities that involve repeated flexion (bending) of the wrist may cause the median nerve to become inflamed and may therefore be a risk factor for CTS. Examples of activities that may lead to CTS include:
- playing a musical instrument
- assembly packing
- using a computer keyboard
- craftwork (making decorative items by hand)
- work that involves manual labour
However, further research into the link between work-related hand use and CTS is required to determine whether these types of activities are a definite cause of the condition.
