Charcot-Marie-Tooth disease, or CMT, is a group of inherited disorders that affect the peripheral nerves, which are the nerves outside the brain and spinal cord. There are more than 70 kinds of CMT. Each kind is caused by a different kind of mutation, and more causes are being discovered every year.
CMT is just one kind of neuropathy (also called peripheral neuropathy). These names simply mean that the peripheral nerves are damaged. There are many other causes of neuropathy besides CMT, including the most common cause—diabetes.
CMT affects all people, all races, and all ethnic groups, throughout the world, affecting about 2.8 million people!
Where Did the Name CMT Come From?
Charcot-Marie-Tooth is named after three physicians who were the first to describe it in 1886: Jean-Martin Charcot, Pierre Marie, and Howard Henry Tooth.
Things in our environment do not cause CMT. CMT is not contagious. CMT is inherited. The most common forms of CMT are passed down from one generation to the next, meaning that it is dominantly inherited.
Some forms of CMT are recessively inherited—a person may be affected even though the parents do not have CMT. In this case, each of the parents harbors a mutation in one of their two copies of a CMT gene. If the child inherits the one mutated CMT gene from each of their parents (the chance of this happening is 1 out of 4), then the child will develop CMT.
Sometimes the mutation that causes CMT happens spontaneously during the process that produces the eggs or sperm. In these rare cases, a child will have CMT even though neither parent has CMT. If a child has such a spontaneous mutation, he/she may pass that mutation down to his/her offspring.
Some types of CMT cause damage to the covering (myelin sheaths) that surrounds nerve fibers. Other kinds of CMT directly damage the nerves fibers themselves. In both cases, the damaged nerve fibers result in neuropathy. The nerves in the legs and arms, which are the longest, are affected first. Nerve fibers that create movement (called motor fibers) and nerve fibers that transmit sensations (called sensory fibers) are both affected. Thus, CMT causes weakness and numbness, usually, starting in the feet.
In the most common kinds of CMT, symptoms usually begin before the age of 20 years. They may include:
- Foot deformity (very high arched feet);
- Foot drop (inability to hold foot horizontal);
- “Slapping” gait (feet slap on the floor when walking because of foot drop);
- Loss of muscle in the lower legs, leading to skinny calves;
- Numbness in the feet;
- Difficulty with balance;
- Later, similar symptoms also may appear in the arms and hands.
CMT almost never affects brain function.
A thorough neurological evaluation by an expert in neuropathy, including a complete family history, physical exam, and nerve conduction tests, with appropriate genetic testing is the way to establish the diagnosis of CMT.
A physical exam may show:
- Difficulty lifting up the foot while walking;
- Difficulty with dorsiflexion of the toes and ankles (upward movement, away from the ground) and other foot movements;
- Reduced or absent deep tendon reflexes (like the knee-jerk reflex);
- Loss of muscle control and atrophy (shrinking of the muscles) in the feet and lower legs (and later the hands).
Genetic testing can provide the exact cause for most people who have CMT.
CMT usually gets worse, slowly, with age; rapid progression is rare, and should motivate a prompt re-evaluation. The problems with weakness, numbness, difficulty with balance, and orthopedic problems can progress to the point of causing disability. Pain can be an issue, as a direct result of the neuropathy (neuropathic pain) and as consequence of orthopedic problems. Other potential complications include the following:
- Progressive inability to walk from weakness, balance problems, and/or orthopedic problems;
- Progressive inability to use hands effectively;
- Injury to areas of the body that have decreased sensation.
There are no known treatments that will stop or slow down the progression of CMT, but the CMTA is funding research to find these treatments.
Physical therapy, occupational therapy, and physical activity may help maintain muscle strength and improve independent functioning.
Orthopedic equipment (such as braces, inserts, or orthopedic shoes) may make it easier to walk.
Orthopedic surgery on the feet can often maintain or even restore function to enable walking.