Overview
Charcot-Marie-Tooth (CMT) disease, also known as hereditary motor and
sensory neuropathy (HMSN), is an inherited, degenerative nerve disorder
that causes muscle weakness and atrophy in the feet, legs, hands, and
forearms. It is characterized by progressive loss of use and sensation
in the limbs.
Charcot, Marie, and Tooth are the names of the physicians who
identified the disease and described its symptoms. It is not the same as
Charcot's foot disease, a neuropathic joint disease that is a common
complication of diabetes mellitus.
In CMT, the myelin coating on motor and sensory
nerves gradually deteriorates, resulting in poor transmission of nerve
impulses. The feet and legs are the first to show the affects of myelin
deterioration, or demyelination. Muscles fail to receive stimulation
from the nerves and then begin to waste away (atrophy). Atrophy in the
small muscles in the feet and hands causes the fingers and toes to curl.
Anatomy
Peripheral nerves extend from the spinal cord throughout the body. Nerve
cells, or neurons, carry impulses to and from the brain via the spinal
cord. Motor neurons signal muscles to move; sensory neurons transmit
sensations, such as heat, pain, and surface texture to the brain. Most
neurons are made up of:
The soma contains a large nucleus and other
structures responsible for proper maintenance and function of the
neuron.
Dendrites are branching structures
that extend from the soma. Dendrites may have hundreds or thousands of
synapses that receive signals from other neurons and relay information
to the soma.
The axon is an elongated structure that
conducts signals from the soma to synaptic terminals. Each neuron has
one axon, which is wrapped in multiple layers of a substance called
myelin. Axons transmit signals at a constant
speed, called nerve conduction velocity (NCV), which is determined by
the diameter of the axon and by the thickness of its myelin sheath.
Myelin is critical in nerve signal conduction.
Synaptic terminals are formed within the
end of an axon. They contain chemicals (neurotransmitters) that relay
signals from one neuron to other neurons or to tissues (i.e., muscles,
glands).
Types
There are two forms of CMT. One form involves degeneration of the myelin
sheath that surrounds a nerve's axon. The other involves impairment of
the axon. There are several types of CMT within each form. The most
commonly diagnosed type is CMT1. In patients with CMT1, there is axonal
demyelination resulting in reduced motor and sensory nerve conduction.
Loss of stimulation by the affected nerves causes muscle weakness and
atrophy.
Incidence and Prevalence
Approximately 125,000 people in the United States have Charcot-Marie-Tooth
disease. CMT occurs slightly more often in men than in women and is not
prevalent in any one race. Signs of the disease usually appear before
the age of 30.
This page was updated on
10/09/2006
