Charcot-Marie-Tooth disease is a genetic disease of the nerves that affects 1 in 2,500 people in the United States. People with this condition experience muscle weakness, particularly in the arms and legs.
The condition affects the peripheral nerves. These nerves are outside the main central nervous system (CNS), and they control the muscles and relay data from the arms and legs to the brain, allowing a person to sense touch.
CMT is also known as Charcot-Marie-Tooth hereditary neuropathy, peroneal muscular atrophy, or hereditary motor and sensory neuropathy. Its name comes from the physicians who first described it: Jean Charcot, Pierre Marie, and Howard Henry Tooth.
The condition is progressive, which means that symptoms gradually worsen over time, but most people with CMT will have a normal lifespan.
It affects males and females equally, and all ethnic groups.
Contents of this article:
Signs and symptoms of CMT
The most common feature of Charcot-Marie-Tooth disease (CMT) is a clear wasting of the limbs, and especially the calf muscles. The patient develops "stork legs." The legs tend to weaken before the arms do.
CMT involves damage to the nerve cells.
Symptoms and their severity may vary considerably between patients, 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.
A child with CMT may:
- Be clumsier than their peers and more prone to accidents
- Have an unusual gait, because of difficulties in lifting 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.
Other symptoms include:
- Weakness in the muscles of the lower feet, legs, and ankles
- Ankles that becomes unstable, because the feet are very highly arched, or less commonly, very flat
- Curled toes, known as hammer toes
- Footdrop, or difficulty lifting the foot because of weak ankle muscles
- A step or stride which is higher than normal
- Numbness in the arms and feet
- Changing leg shape, with the leg becoming very thin below the knee, while the thighs retain their normal muscle volume and shape.
In time, the following may happen:
- The hands and arms become weaker.
- It becomes harder to use the hands, for example, to do up buttons or open jars and bottle tops.
- There is muscle and joint pain, as problems with walking and posture place a strain on the body.
- Neuropathic pain results from damaged nerves
- General walking and mobility problems occur, especially in older patients.
In severe cases, the patient may need a wheelchair, while others may use a leg brace, special shoes, or other orthopedic devices.
Risk factors and causes of CMT
CMT is a hereditary disease, so people who have close family members with CMT have a higher risk of developing it.
A person with CMT may need to use a wheelchair.
The disorder 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.
CMT 1 accounts for about 1 in 3 cases. In CMT1, mutated, or faulty, genes cause the myelin sheath to disintegrate. As the myelin 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.
In CMT 2, the faulty gene affects the axons directly. The signals are not transmitted strongly enough to activate muscles and senses, so patients have weaker muscles and a poorer sense of touch, or numbness. CMT 2 accounts for around 17 percent of cases.
CMT 3, or Dejerine-Sottas disease, is a rare type of CMT. Damage to the myelin sheath leads to severe muscle weakness, and the sense of touch is also affected severely. Symptoms may be noticeable in children.
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 very mild symptoms.
How is CMT diagnosed?
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 there is a chance that the patient may have CMT, they will need to see a neurologist for further tests.
Nerve conduction studies measure the strength and speed of the electrical signals that pass through the nerves. Electrodes are placed on the skin, and these deliver tiny electric shocks that stimulate the nerves. A delayed or weak response suggests a nerve disorder, and possibly CMT.
Electromyography (EMG) 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 will involve a small piece of peripheral nerve being taken from the calf, for testing in a lab.
Genetic testing is done by using a blood sample. This may show whether the patient carries the faulty gene, or genes.
What is the treatment for CMT?
There is no cure for CMT, but treatment may relieve symptoms and delay the start of physical disabilities.
Physical therapy, such as stretching, can help maintain muscle condition.
NSAIDs (non-steroidal anti-inflammatory drugs), such as ibuprofen, can help reduce joint and muscle pain, as well as pain caused by damaged nerves.
Tricyclic antidepressants (TCAs) may be prescribed if NSAIDs are not effective. TCAs are normally used to treat depression, but they may alleviate neuropathic pain symptoms. However, they may have side effects.
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.
Devices, such as orthopedic devices, braces or splints, can help the individual to stay mobile, and they can 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.
Patients who also have scoliosis, or curvature of the spine, may need a back brace and sometimes surgery.
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.
Possible complications of CMT
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.
Cognitive behavioral therapy (CBT) can help patients with CMT to cope better with everyday life and, if necessary, with depression.
Although CMT cannot be cured, 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, and not drinking too much alcohol.