Carpal Tunnel Syndrome - Causes and Diagnosis

What is the carpal tunnel?

There are eight small bones called carpal bones in the wrist. A ligament (also called retinaculum) lies across the front of the wrist. Between this ligament and the carpal bones is a space called the carpal tunnel. The tendons that attach the forearm muscles to the fingers pass through the carpal tunnel. A main nerve (median nerve) to the hand also goes through this tunnel before dividing into smaller branches in the palm.

The median nerve gives feeling to the thumb, index and middle fingers, and half of the ring finger. It also controls the movement of the small muscles at the base of the thumb.

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What causes carpal tunnel syndrome?

  • In most cases it is not clear why it occurs. It is thought that some minor changes occur in the tendons and/or other structures going through the carpal tunnel. This may cause an increase in pressure within the tunnel. The increase in pressure is thought to squash (compress) and restrict the blood supply to the median nerve. As a result, the function of the median nerve is affected causing the symptoms.
  • Your genes may play a part. There seems to be some inherited (genetic) factor. About 1 in 4 people with carpal tunnel syndrome have a close family member (father, mother, brother, sister) who also has or had the condition.
  • Bone or arthritic conditions of the wrist, such as rheumatoid arthritis or wrist fractures, may lead to carpal tunnel syndrome.
  • Various other conditions are associated with carpal tunnel syndrome. For example: pregnancy, obesity, an underactive thyroid gland, diabetes, the menopause, other rare diseases, and a side-effect of some medicines. Some of these conditions cause water retention (oedema) which may affect the wrist and cause carpal tunnel syndrome.
  • Rare causes include cysts, growths, and swellings coming from the tendons or blood vessels passing through the carpal tunnel.

Do I need any tests?

Often the symptoms are so typical that no tests are needed to confirm the diagnosis.

If the diagnosis is not clear then a test to measure the speed of the nerve impulse through the carpal tunnel (nerve conduction test) may be advised. A slow speed of impulse down the median nerve will usually confirm the diagnosis. Some people may also be referred for an ultrasound scan or an MRI scan to look at their wrist in more detail.

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Author:
Dr Laurence Knott
Peer Reviewer:
Dr Louise Newson
Document ID:
4211 (v43)
Last Checked:
08 July 2017
Next Review:
07 July 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.