Charcot-Marie-Tooth disease - Diagnosing Charcot-Marie-Tooth disease

If you have early symptoms of Charcot-Marie-Tooth disease (CMT), your GP will ask about your symptoms and whether there is a family history of it.

Your GP may want to know when your symptoms started, how severe your symptoms are and if anyone in your family has CMT. They may then carry out a physical examination.

During the examination, your GP will be looking for evidence of the condition, such as muscle weakness, poor or absent reflexes, and foot deformities such as high arches or flat feet.

Further tests

If CMT is suspected, you may be referred to a neurologist (a doctor who specialises in treating conditions of the nervous system) for further testing. Tests you may have are described below.

Nerve conduction test

A nerve conduction test measures the strength and speed of signals transmitted through your peripheral nerves (network of nerves that run from the brain and spinal cord to and from the rest of the body, such as the limbs and organs).

Electrodes (small metal discs) are placed on your skin, which release a small electric shock that stimulates the nerves. The speed and strength of the nerve signal is then measured. An unusually slow or weak signal could indicate CMT.

Electromyography (EMG)

Electromyography (EMG) uses a small needle-shaped electrode placed in your skin to measure the electrical activity of your muscles. Some types of CMT cause a distinctive change in the pattern of electrical activity that can be detected by an EMG.

Genetic testing

Genetic testing involves taking your blood sample and testing it for defective genes known to cause CMT. So far, many of these genes have been found, but there may be more not yet identified.

It is estimated that most people with CMT will be able to have their diagnosis confirmed by genetic testing, and find out exactly which type of CMT they have. For others, genetic testing may prove inconclusive because an unidentified gene may be involved in their CMT.

Nerve biopsy

In a small number of cases where other tests have been inconclusive, a test called a nerve biopsy may be carried out.

This is a minor surgical procedure where a sample of a peripheral nerve is removed from your leg for testing. CMT can cause physical changes to the shape of the nerve, which can be seen under a microscope. The biopsy is carried out under a local anaesthetic, so you will be awake but unable to feel pain.

Being diagnosed with CMT

Everyone reacts differently when told they have CMT. You may experience feelings of shock, denial, confusion or fear. Some people are relieved that there is finally an explanation for their symptoms.

You may find the following advice useful if you have recently been diagnosed with CMT:

• take all the time you need – don't rush into making important decisions about your health
• find any support you need – talk to your family and friends when you feel ready; you may also find it helpful to contact other people with CMT through the charity CMT UK
• find out what you can about CMT – both from your healthcare team and reliable online resources such as CMT UK
• get involved in your care – work closely with your healthcare team to come up with a treatment plan that best suits you

CMT UK has more information on coping with a diagnosis.

Tests before and during pregnancy

Couples with a family history of CMT who are thinking of having a baby can be referred to a genetics specialist for advice.

A genetic counsellor can help couples work through the decision-making process and explain possible tests that can be carried out and any alternatives you may want to consider, such as adoption. Read more about genetic testing and counselling.

The main tests that can be carried out during pregnancy to check if a baby will develop certain types of CMT are:

• chorionic villus sampling (CVS) – where a small sample of placenta is removed from the womb and tested for known CMT genes, usually between weeks 11 to 14 of pregnancy
• amniocentesis – where a sample of amniotic fluid is taken for testing, usually during weeks 15 to 20 of pregnancy

If these tests show your child is likely to have CMT, you can discuss with your genetic counsellor whether you want to continue the pregnancy or have an abortion.

However, it's important to be aware that the results of these tests will not indicate how serious your child's CMT will be. This is because the symptoms and progression of the condition can vary widely, even among family members with the same type of CMT.

It's also important to bear in mind that both these tests can slightly increase your chances of having a miscarriage.

Pre-implantation genetic diagnosis

For some couples at risk of having a child with CMT, pre-implantation genetic diagnosis (PGD) may be an option.

PGD involves using in-vitro fertilisation (IVF), where eggs are removed from a woman's ovaries before being fertilised with sperm in a laboratory. After a few days, the resulting embryos can be tested for certain types of CMT and a maximum of two unaffected embryos are transferred into the womb.

However, funding for PGD is decided on an individual basis. For example, you may be considered ineligible for PGD on the NHS if you already have unaffected children or if the chances of having a successful pregnancy are thought to be low. In these cases you can choose to fund PGD yourself, although each attempt is likely to cost at least £8,000.