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Neuromuscular Diseases

Progressive Muscular Atrophy

Although there are several variations of this disorder, they all show wasting of the muscles ("atrophy") secondary to degeneration of the motor nerve system. The most common type is called amyotrophic lateral sclerosis and is popularly known as Lou Gehrig disease. Onset generally occurs between ages 40-70, but the disease can begin at other times in life. Although it may begin on one side, it always becomes bilateral. It is always fatal (within 2-5 years after diagnosis), since it spreads upward to involve throat and other vital muscles.

Charcot-Marie-Tooth disease (CMT) is named after the three doctors who first described it in 1886, Professor Jean-Martin Charcot (pronounced sharko) (1825-1893), his student, Pierre Marie (1853-1940), who both worked in Paris at the Hospital de Salpetriere, and Dr. Howard Tooth (1856-1925) of London. It is also called peroneal muscular atrophy (PMA) because the peroneal muscle down the front of the shin that enables one to pull the foot up is usually the first muscle to be affected. A weakened peroneal muscle can cause sloppy walking or drop foot, which causes tripping. CMT also has a third and more recent name, hereditary motor and sensory neuropathy(HMSN). This name more accurately describes the syndrome because it is hereditary, can affect both or either the ability to move (motor) or the ability to feel (sensory).

CMT is primarily a disease of the nerves whereby the myelin or insulating sheath of myelin on the nerves does not stay intact and the messages from the brain to the muscles through the nerves are not carried properly. It differs from muscular dystrophy in that people who have CMT are born with normal muscles. The muscles atrophy because the CMT affected nerves that serve them cannot properly send the message from the brain for them to move. Therefore, muscles can atrophy even though they are being used. People with muscular dystrophy have a problem with their muscles from the beginning. CMT is a muscular atrophy not a muscular dystrophy.

CMT is not well known but it is not rare. Many people do not know they have it even though it is carried in families sometimes for generations. CMT can be inherited three ways but most cases are inherited autosomal dominate pattern meaning it comes directly down a line from parent to child. In this form of inheritance there is a 50/50 chance at each conception that the child will have CMT.

Outward signs are what doctors look for to begin a diagnosis of CMT. The primary signs for CMT are: loss of muscle in the calf area giving the leg a very thin look from the knee down, a drop foot walk, high arches or very flat feet and other foot bone deformities, cocked or hammertoes, ankle weakness and loss of feeling and/or movement in the foot and ankle. Primary signs in the upper extremities are finger, hand and grip as well as wrist weakness, the loss of the muscle that lets the thumb move and a loss of feeling and/or movement in the hand and wrist. Balance is usually affected because the muscles of the feet are weak and cannot compensate for a sudden stop or a change in the terrain.

Fatigue is one of the prime symptoms that everyone who has CMT seems to experience. Scoliosis and other spinal deformities are often diagnosed in people who show CMT at an early age and some people experience hip and knee dislocations while some are born with deformed hip sockets. Diagnosis can also be made by doing an electromyogram (EMG) that measures the irritability and function of muscles and motor nerve-conduction velocity (MNCV) tests that establish the ability of nerves to send and receive impulses.

CMT does not affect life expectancy unless the phrenic nerves that help you breathe are badly involved. Also, some people who have CMT lose the ability to cough. Not being able to cough and weakened respiratory function can mean a person is more susceptible to life-threatening lung infections and disease. With an early diagnosis and by taking care of oneself over the years, most people with CMT will live a normal life span without too much difficulty, although there is no denying the fact that some people do have severe problems. Surgery can help foot, ankle, hand, finger, spine and hip problems. Ankle-foot orthotics (AFOs) can also help a person with footdrop walk without tripping and in-shoe orthotics can help alleviate pain experienced when walking and give a person an improved gait. Genetic research has already found the genes that cause some of the many types of CMT and is ongoing. Testing for some types is available.

See also Muscular system.


Resources

Books

Adams, Raymond D., and Maurice Victor. Principles of Neurology. New York: McGraw-Hill, 1989.

Klawans, Harold W. Toscanni's Fumble and Other Tales of Clinical Neurology. Chicago: Contemporary Books, 1988.


Joseph D. Wassersug

KEY TERMS


Acetylcholine (ACh)

—A white crystalline chemical compound (C7H17NO3) that transmits nerve impulses across intercellular gaps and activates muscular contraction.

Actin

—A muscle protein, active with myosin, in muscle contraction.

Action potential

—A transient change in the electrical potential across a membrane which results in the generation of a nerve impulse.

Cholinesterase

—An enzyme that destroys acetylcholine and keeps it from accumulating at neuromuscular interfaces.

Creatine

—A nitrogenous, organic acid found in the muscle tissue of many vertebrates. Blood levels increase when muscle is damaged.

Creatine kinase

—A enzyme that is found and easily measured in blood and other tissues. It increases quantitatively when there is muscle destruction.

Dystrophin

—An abnormal encoded protein isolated from the Duchenne gene at the Xp21 locus.

Glycogen

—A starchy substance that is synthesized and stored in the muscles and a ready source of energy for muscular contraction.

Neuromuscular junction

—Where the nerve fibers terminate in the muscle tissue.

Neuron

—A nerve cell consisting of a nucleated portion from which there extrude smaller extensions called dendrites and longer processes called axons. Neurons may be either sensory or motor.

Plasmalemma

—Outer sheath or membrane of muscle tissue.

Sarcolemma

—Muscle tissue enclosed by muscle sheath and closely related to another substance called sarcoplasma.

Additional topics

Science EncyclopediaScience & Philosophy: Mysticism to Nicotinamide adenine dinucleotideNeuromuscular Diseases - The Motor Unit, Causes Of Neuromuscular Dysfunction, Muscular Dystrophy, The Neuromyopathies, Progressive Muscular Atrophy - The neuropathies: symptoms and clinical findings