Charcot Marie Tooth Disease (CMT) is the most common inherited neurological disorder, causing weakness and loss of sensation in the feet, legs and hands.
It affects approximately 1 in every 2,500 people and was first identified in 1886 by three doctors Jean-Marie Charcot, Pierre Marie and Howard Henry Tooth. It is also known as peroneal muscular atrophy.
Charcot Marie Tooth disease develops gradually, usually starting with symptoms of weakness and decreased sensation in the feet which can spread progressively over time up the legs, sometimes also affecting the hands and arms. It often results in abnormalities in the shape of the foot such as high foot arches.
There is no cure for Charcot Marie Tooth Disease but there are a number of treatment options available to reduce symptoms. Here, we will look at the causes, symptoms, diagnosis and treatment options for peroneal muscular atrophy.
Charcot Marie Tooth Disease is a type of peripheral neuropathy. Let me explain. Our bodies are made up of two nervous systems, the central nervous system (brain and spinal cord) and the peripheral nervous system (nerve fibres that travel round the body). In CMT disease, there is a problem with the peripheral nervous system. There are two types of nerve in the peripheral nervous system, motor nerves (which control movement) and sensory nerves (which interpret touch such as heat, cold and pressure).
Our nerves work by sending messages in the form of electrical signals from the central nervous system to the rest of the body through the peripheral nervous system. Think of them like a telephone cable. The wires inside, known as the axon, transmit the electrical signals from one place to another. The protective outer covering, known as the myelin sheath, protects and insulates the wires from damage so the signals can transmit without interruption. It also allows signals to transmit quicker.
In Charcot Marie Tooth Disease, there may be a problem with:
1) The Myelin Sheath: This breaks down exposing the axon to damage which affects the transmission of signals down the nerve
2) The Axon: which reduces the strength of the electrical signals
Charcot Marie Tooth disease is caused by a problem with genes. We are made up of around 30,000 pairs of genes. For each pair, we inherit one copy from our mother and one from our father to make a pair, so we have two copies of every gene. Charcot Marie Tooth disease can be caused by a mutation of a number of different genes. The mutation affects the production of the proteins that form the axon and myelin sheaths in the peripheral nerves. Gradually over time, the nerves degenerate, reducing their ability to transmit signals.
There are three ways that we can inherit the genetic mutations that cause Charcot Marie tooth disease
1) Autosomal Dominant Inheritance: This is the most common cause of CMT disease and is where a mutation of one of the inherited genes in the pair is sufficient to cause the disease. If one parent carries the mutated gene, there is a 50% chance of the disease being passed on
2) Autosomal Recessive: This requires a mutation of both of the copies of the gene in a pair, i.e. both parents would have to pass on affected genes. If both parents had mutated CMT genes, there is a 50% chance of their child being a carrier (carrying one CMT gene but not displaying any symptoms), 25% chance of having CMT disease and 25% chance of inheriting two normal genes. If only one parent had a recessive CMT gene, their child would not develop CMT disease but would have a 50% chance of being a carrier
3) X-Linked Inheritance: The mutated gene is linked to the X chromosome (female), not the Y chromosome (male). Males are made up of XY chromosomes and females have XX chromosomes. When CMT disease is linked with an X chromosome, there is a 50% chance of a mother passing the disease on. If she passes the gene on to a son, he will be symptomatic. If she passes the gene on to a daughter, she is likely to only have mild symptoms as the unaffected X chromosome tends to override the condition
Very rarely a gene may mutate spontaneously causing peripheral muscular atrophy, rather than being passed down genetically.
There are five main types of Charcot Marie Tooth Disease
1) CMT 1: This is the most common type of Charcot Marie Tooth Disease accounting for 30% of cases. Gene duplication causes the myelin sheath to break down, known as demyelination. The body responds with a proliferation of Schwann cells which wrap around the axon resulting in remyelination. The cycle keeps repeating producing what is known as the onion bulb effect
2) CMT 2: Results from abnormalities in the axon itself. It accounts for 20-40% of cases
3) CMT 3: develops in infancy and results in severe demyelination and thinning of the myelin sheath. It is the most severe form of Charcot Marie Tooth Disease causing severe muscle wasting and weakness as well as sensory problems. It is also known as Dejerine-Sottas disease and is extremely rare
4) CMT 4: this is a rare type of Charcot Marie tooth disease that affects the myelin sheath
5) CMT X: This is another demyelinating neuropathy caused by a mutation in the X chromosome, more commonly affecting men. It accounts for 10-20% of cases
The symptoms of Charcot Marie Tooth disease varying depending on the type of disease, but there are many shared characteristics. Symptoms develop gradually, usually starting during childhood and get progressively worse over time. Symptoms usually appear between the ages of 5 and 15 and include:
1) Changes in Foot Position: either very high or flat foot arches
2) Muscle Weakness: Wasting of the muscles results in weakness. This starts in the feet and ankles and can gradually spread up the legs, resulting in what is referred to as an upside-down champagne bottle appearance of the legs due to muscle wasting. Weakness may also develop in the hands and forearms, making fine motor control activities like writing difficult
3) Difficulty Walking: Muscle weakness often leads to difficulty walking and can result in frequent trips, falls and ankle sprains due to an inability to pick the foot up effectively, known as a foot drop. Clumsiness is often one of the first signs of Charcot Marie Tooth disease in children
4) Curled Toes: The position of the toes can change known as hammertoe
5) Altered Sensation: Decreased or absent sensation (ability to feel touch or temperature) in the feet and hands
6) Spinal Deformity: Curvature of the spine (known as scoliosis) affects up to half of CMT disease sufferers
7) Cramp: Muscle cramping commonly occurs with CMT disease
8) Pain: Pain may be experienced, usually associated with postural changes, weakness and cramp
9) Altered Reflexes: Reflexes such as the knee and ankle jerk may be decreased or absent
CMT 3 presents during infancy, usually by the age of two resulting in floppy baby syndrome and delayed motor skills.
Whilst symptoms progress over time, in most cases, Charcot Marie Tooth Disease does not affect life expectancy. Occasionally however, it can cause breathing problems.
Diagnosis starts with your doctor asking you about your symptoms and any
family history of the disease. Examination will start with observation
of your foot position, testing muscle strength, reflexes and sensory
testing. They will also look for signs of enlarged nerves that can be
seen or felt through the skin.
If your doctor suspects Charcot Marie Tooth Disease, you will be referred to a neurologist (a specialist doctor of the nervous system). They will carry out further tests which may include:
1) Nerve Conduction Tests: This is where they look at the speed and strength of the signals transmitted through the peripheral nerves. This is done using electrodes placed on the skin which produce small electric shocks to stimulate the nerves. Slow or weak signals may indicate CMT disease
2) Electromyogram (EMG): This tests the electrical activity at your muscles at rest and when contracting. Small needles connected to a machine are placed in your muscles. They measure the muscles electrical activity at rest and then when you try and contract the muscle. Specific patterns of activity can be seen in some types of CMT disease
3) Nerve Biopsy: If nerve conduction and EMG tests have been inconclusive, a nerve biopsy may be performed. This is when a small section of a peripheral nerve is removed under local anaesthetic and examined under a microscope for signs of Charcot Marie Tooth disease
4) Gene Testing: Genetic testing from a blood sample can be used to diagnose most types of CMT disease, but not all genes that cause the disease have been identified yet
There is currently no cure for Charcot Marie Tooth disease, but a
combination of therapy, orthotics, surgery and medication can help to
reduce symptoms. Treatment may include:
Rehab programmes are a vital part of CMT treatment. Strengthening exercises help combat the weakness associated with the disease. They are most effective when started early, before the muscles have a chance to waste. Daily stretches, particularly for the calf muscles and Achilles tendon should be done to prevent muscle contractures. General fitness programmes also help to reduce fatigue from the extra effort required for movement. Low impact activities such as cycling and swimming are recommended to limit the force put through the joints. It can also help to work on balance and posture to prevent injuries or associated problems.
This looks at ways to make your activities of daily living such as
washing and dressing easier, through practical methods and using
Shoe insoles to correct your foot position (such as a AFO) and ankle or knee braces can
be useful for providing support and stability of the foot and leg and
make activities such as walking easier and help reduce the risk of
injury for people suffering from Charcot Marie Tooth disease.
Analgesics may be prescribed to reduce pain associated with the disease. Neurotoxic drugs such as vincristine should be avoided as they can make the condition worse.
Sometimes surgery is necessary to combat structural deformities of the foot and ankle. Bone surgery such as an osteotomy or arthrodesis helps correct the shape of the foot such as realigning hammertoes, correcting severely fallen foot arches or fusing the ankle joint for stability. Soft tissue release is done if muscles and tendons have become too type such as plantar fascia release. Spinal surgery may be required if a scoliosis has developed.
Exercises can make a big difference for people suffering from Charcot Marie Tooth disease. Exercise programmes should be carried out under the guidance of a physiotherapist, but visit the strengthening exercises and ankle stretches for some suggestions of things that might help.
If peroneal muscular atrophy is not sounding quite like your problem, visit the foot pain diagnosis section for help working out what is wrong, or the common foot problems section.
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