During initial stages of diagnosing Charcot-Marie-Tooth disease (CMT), your GP will ask about your symptoms and whether there is any history of CMT in your family.
Your GP may want to know:
- when your symptoms started
- how severe your symptoms are
- if anyone in your family has CMT
Physical examination
After asking about your symptoms and family history, your GP will carry out a physical examination. During the examination, your GP will be looking for evidence of the condition, such as:
- muscle weakness
- reduced muscle tone
- missing reflexes
- 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 periphery nerves (the 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.
Nerve biopsy
A nerve biopsy is a minor surgical procedure where a sample of a periphery 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.
Genetic testing
Genetic testing involves taking your blood sample and testing it for defective genes (units of genetic material) known to cause CMT. So far, around 25 of these genes have been found. However, there may be more not yet identified.
It is estimated that 70% of people with CMT may 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.
Pre-natal testing
Pre-natal testing may help determine whether an unborn baby has CMT. This may be useful if you or your partner has CMT, or if you know you are carrying a gene that causes it, and are going to become a parent.
Two tests which may be used:
These tests are described briefly below.
Chorionic villus sampling (CVS)
Pre-natal testing for conditions such as CMT can be carried out around 10 to 13 weeks into the pregnancy using chorionic villus sampling (CVS).
CVS involves taking a sample of cells from the placenta (the organ that links the mother’s blood supply with her unborn baby’s). The sample is tested for genetic (inherited) conditions.
Amniocentesis
Amniocentesis can also be used to test for CMT. This test is carried out around 15-18 weeks into the pregnancy. It involves taking a small sample of amniotic fluid (the fluid that surrounds the unborn baby in the womb) for examination.
Caution
It is important to remember that although these tests may help determine whether your child has the defective gene, they will not indicate how serious the 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.
