What is Charcot-Marie-Tooth Disease (CMT)?
Charcot-Marie-Tooth (CMT) affects the peripheral nerves. These are the nerves outside the main central nervous system (CNS). They control the muscles and relay data from the arms and legs to the brain, allowing a person to sense touch. It is a progressive condition, which means that symptoms get worse over time.
CMT is also known as Charcot-Marie-Tooth hereditary neuropathy, peroneal muscular atrophy, or hereditary motor and sensory neuropathy. Its name comes from the three physicians who first described it: Jean Charcot, Pierre Marie, and Howard Henry Tooth.
Most people with CMT will have a normal lifespan.
The impact it will have depends on the type and how severe it is.
- Charcot-Marie-Tooth (CMT) is a neurological condition.
- It leads to muscle wasting, especially in the lower legs.
- It tends to run in families.
- The impact it will have depends on the type and how severe it is.
Hand weakness can be a symptom of CMT.
Symptoms often appear in adolescence or early adulthood.
Key symptoms include:
- Weakness and eventual wasting of muscles in the foot, lower leg, hand, and forearm
- Loss of sensation in the fingers, toes, and limbs
Other symptoms may include:
- abormalities in the muscles of the feet, leading to high arches and hammer toes
- difficulty using the hands
- unstable ankles and problems with balance
- cramping in the lower legs and forearms
- some vision and hearing loss
- reduced reflexes
Symptoms and their severity may vary considerably between individuals, even among close relatives who have inherited the condition.
In the early stages, people might not know that they have CMT, because the symptoms are so mild.
Symptoms in children
If symptoms appear during childhood the child may:
- be clumsier than their peers and more prone to accidents
- have an unusual gait, as it is hard to lift their feet off the ground with each step
- have feet that drop forward as they lift their feet
Other symptoms often appear as the child finishes puberty and enters adulthood, but they can emerge at any age, from very young to the late 70s.
In time, the leg may change shape, becoming very thin below the knee, while the thighs retain their normal muscle volume and shape.
Symptoms tend to worsen over time, and there may be:
- growing weakness in the hands and arms
- increased difficulty in using the hands, for example, to do up buttons or open jars and bottle tops
- muscle and joint pain, as problems with walking and posture place a strain on the body
- neuropathic pain due to damaged nerves
- walking and mobility problems, especially in older people
Assistive devices may include a wheelchair, a leg brace, special shoes, or other orthopedic devices.
CMT is hereditary, so people who have close family members with CMT have a higher risk of developing it.
It affects the peripheral nerves. A peripheral nerve consists of two main parts, the axon, which is the inside of the nerve, and the myelin sheath, which is the protective layer around the axon.
CMT can affect the axon, the myelin sheath, or both, depending on the type of CMT.
There are many types of CMT. Here are the main forms.
CMT 1 accounts for about 1 in 3 cases. Symptoms often appear between the ages of 5 and 25 years. Faulty, genes cause the myelin sheath to disintegrate. As the sheath wastes away, eventually the axon becomes damaged and the patient's muscles no longer receive clear messages from the brain. This results in muscle weakness and loss of sensation, or numbness. Fewer than 1 in 20 people will need a wheelchair.
Subtypes of CMT1 include CMT1A and CMT1B. They are caused by different genetic changes, and symptoms can vary.
CMT 2 accounts for around 17 percent of cases. The faulty gene affects the axons directly. The signals are not transmitted strongly enough to activate muscles and senses, so the individual has weaker muscles and a poorer sense of touch, or numbness.
CMT 3, or Dejerine-Sottas disease, is a rare type of CMT. Damage to the myelin sheath leads to severe muscle weakness. The sense of touch is also affected severely. Signs are usually noticeable in infancy.
CMT 4 is a rare condition that affects the myelin sheath. Symptoms generally appear during childhood, and patients often need a wheelchair.
CMT X is caused by an X-chromosome mutation. It is more common in males. A female with CMT X will have mild or no symptoms.
A physician will ask about family history, and will look for evidence of muscle weakness, reduced muscle tone, flat feet, or high feet arches.
If the person may have CMT, they will need to see a neurologist and a geneticist for further tests.
Nerve conduction studies: These measure the strength and speed of the electrical signals that pass through the nerves. Electrodes placed on the skin, deliver tiny electric shocks that stimulate the nerves. A delayed or weak response suggests a nerve disorder, and possibly CMT.
Electromyography (EMG): This involves inserting a thin needle into the targeted muscle. As the patient relaxes or tightens the muscle, electrical activity is measured. Testing different muscles will reveal which ones are affected.
A biopsy: This involves taking a small piece of peripheral nerve from the calf, for testing in a lab.
Genetic testing: A blood sample is taken to find out whether the person carries the faulty gene or genes.
There is no cure for CMT, but treatment may relieve symptoms and delay the start of physical disabilities.
Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, can help reduce joint and muscle pain and pain caused by damaged nerves.
Physical therapy uses low-impact exercises to help strengthen and stretch the muscles. This can help to maintain muscle strength for longer and prevent muscle tightening.
Occupational therapy may help patients who have problems with finger movements and gripping, because this can make it very hard to carry out daily activities.
Assistive devices, such as orthopedic devices, braces or splints, can help the individual stay mobile and prevent injury. Shoes with high tops or special boots provide extra ankle support, and special shoes or shoe inserts can improve gait. Thumb splints may help with dexterity.
Cognitive behavioral therapy (CBT) can help patients with CMT to cope better with everyday life and, if necessary, with depression.
Surgery to fuse bones in the feet or to remove part of a tendon can sometimes alleviate pain and make walking easier. Surgery can correct flat feet, relieve joint pain and correct heel deformities.
Patients who also have scoliosis, or curvature of the spine, may need a back brace and sometimes surgery.
People with CMT may experience a number of complications.
Breathing may be difficult if the condition affects the nerves that control the diaphragm. The patient may need bronchodilator medication or a ventilator. Being overweight or obese may make breathing worse.
CMT does not usually affect a person's lifespan, but the outlook depends on how severe the condition is.
For some people with CMT1, for example, symptoms will be so mild that they will not notice that they have the condition. Among those with CMT1, fewer that 5 percent will need to use a wheelchair.
CMT cannot be cured, but some measures may help to avoid further problems. These include:
- taking good care of the feet, as there is an increased risk of injury and infection avoiding caffeine and tobacco
- limiting alcohol intake
Help and support are available from organizations such as the Charcot-Marie-Tooth Association.