Page 4 - A Guide to Physical and Occupational Therapy for CMT

Understanding

the Cause

CMT is caused by mutations in specific genes that affect the transmission
of signals up and down nerves in the body outside of the spinal cord. There
are many different forms of CMT, each type corresponding to a specific gene
mutation; however, the two most common forms of CMT can be characterized
as follows:

Demyelinating forms reduce the myelin sheath, impairing the conduction of
signals down a nerve. The myelin sheath is the coating around a nerve. To use
an analogy: think of nerves like the wires inside the cord you use to charge your
cell phone. The myelin sheath is the exterior, rubbery coating that surrounds
the wires. When the myelin covering the nerves is damaged or absent, the
messages being conducted are either delayed or cannot reach their destination
– in this case, the muscles. Unable to receive the messages, muscles do not
function normally and often weaken and atrophy.
Axonal forms damage the nerves themselves. To continue the phone cord
analogy, this would be similar to having faulty wires inside the cord that prevent
the charge from reaching your phone. Similarly, damage to the nerves prevents
messages from reaching the muscles, often resulting in muscular weakness
and atrophy as well as loss of sensation.

Signs & Symptoms
CMT affects the longer nerves first; therefore, symptoms tend to start in the feet
and hands and work their way up the legs and into the forearms.

Symptoms include:
• Weakness in the feet, ankles and legs
• Difficulty lifting the foot at the ankle during walking (foot drop)
• Depressed tendon reflexes
• Absence of development or loss of muscle bulk in the feet and legs
• An awkward “steppage” gait
• High-arched (pes cavus) feet or flat feet
• Curled toes
• Calluses and blisters on the feet
• Frequent tripping or falling
• Decreased ability to run
• Decreased sensation or a loss of feeling in the feet and legs
• Discomfort/pain in the feet
• Frequent twisting of the ankles and sprains
• Muscle cramping, especially in feet and lower legs