muscular dystrophy

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Related to Muscular distrophy: multiple sclerosis, Duchenne muscular dystrophy

Muscular Dystrophy

 

Definition

Muscular dystrophy is the name for a group of inherited disorders in which strength and muscle bulk gradually decline. Nine types of muscular dystrophies are generally recognized.

Description

The muscular dystrophies include:
  • Duchenne muscular dystrophy (DMD): DMD affects young boys, causing progressive muscle weakness, usually beginning in the legs. It is the most severe form of muscular dystrophy. DMD occurs in about 1 in 3,500 male births, and affects approximately 8,000 boys and young men in the United States. A milder form occurs in very few female carriers.
  • Becker muscular dystrophy (BMD): BMD affects older boys and young men, following a milder course than DMD. BMD occurs in about 1 in 30,000 male births.
  • Emery-Dreifuss muscular dystrophy (EDMD): EDMD affects young boys, causing contractures and weakness in the calves, weakness in the shoulders and upper arms, and problems in the way electrical impulses travel through the heart to make it beat (heart conduction defects). Fewer than 300 cases of EDMD have been identified.
  • Limb-girdle muscular dystrophy (LGMD): LGMD begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles around the hips and shoulders. It is the most variable of the muscular dystrophies, and there are several different forms of the disease now recognized. Many people with suspected LGMD have probably been misdiagnosed in the past, and therefore the prevalence of the disease is difficult to estimate. The number of people affected in the United States may be in the low thousands.
  • Facioscapulohumeral muscular dystrophy (FSH): FSH, also known as Landouzy-Dejerine disease, begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles of the face, shoulders, and upper arms. The hips and legs may also be affected. FSH occurs in about 1 out of every 20,000 people, and affects approximately 13,000 people in the United States.
  • Myotonic dystrophy: also known as Steinert's disease, affects both men and women, causing generalized weakness first seen in the face, feet, and hands. It is accompanied by the inability to relax the affected muscles (myotonia). Symptoms may begin from birth through adulthood. It is the most common form of muscular dystrophy, affecting more than 30,000 people in the United States.
  • Oculopharyngeal muscular dystrophy (OPMD): OPMD affects adults of both sexes, causing weakness in the eye muscles and throat. It is most common among French Canadian families in Quebec, and in Spanish-American families in the southwestern United States.
  • Distal muscular dystrophy (DD): DD begins in middle age or later, causing weakness in the muscles of the feet and hands. It is most common in Sweden, and rare in other parts of the world.
  • Congenital muscular dystrophy (CMD): CMD is present from birth, results in generalized weakness, and usually progresses slowly. A subtype, called Fukuyama CMD, also involves mental retardation. Both are rare; Fukuyama CMD is more common in Japan.

Causes and symptoms

Causes

Several of the muscular dystrophies, including DMD, BMD, CMD, and most forms of LGMD, are due to defects in the genes for a complex of muscle proteins. This complex spans the muscle cell membrane to unite a fibrous network on the interior of the cell with a fibrous network on the outside. Current theory holds that by linking these two networks, the complex acts as a "shock absorber," redistributing and evening out the forces generated by contraction of the muscle, thereby preventing rupture of the muscle membrane. Defects in the proteins of the complex lead to deterioration of the muscle. Symptoms of these diseases set in as the muscle gradually exhausts its ability to repair itself. Both DMD and BMD are caused by flaws in the gene for the protein called dystrophin. The flaw leading to DMD prevents the formation of any dystrophin, while that of BMD allows some protein to be made, accounting for the differences in severity and onset between the two diseases. Differences among the other diseases in the muscles involved and the ages of onset are less easily explained.
The causes of the other muscular dystrophies are not as well understood:
  • One form of LGMD is caused by defects in the gene for a muscle enzyme, calpain. The relationship between this defect and the symptoms of the disease is unclear.
  • EDMD is due to a defect in the gene for a protein called emerin, which is found in the membrane of a cell's nucleus, but whose exact function is unknown.
  • Myotonic dystrophy is linked to gene defects for a protein that may control the flow of charged particles within muscle cells. This gene defect is called a triple repeat, meaning it contains extra triplets of DNA code. It is possible that this mutation affects nearby genes as well, and that the widespread symptoms of myotonic dystrophy are due to a range of genetic disruptions.
  • The gene for OPMD appears to also be mutated with a triple repeat. The function of the affected protein may involve translation of genetic messages in a cell's nucleus.
  • The cause of FSH is unknown. Although the genetic region responsible for it has been localized on its chromosome, the identity and function of the gene or genes involved had not been determined as of 1997.
  • The gene responsible for DD has not yet been found.

Genetics and patterns of inheritance

The muscular dystrophies are genetic diseases, meaning they are caused by defects in genes. Genes, which are linked together on chromosomes, have two functions: They code for the production of proteins, and they are the material of inheritance. Parents pass along genes to their children, providing them with a complete set of instructions for making their own proteins.
Because both parents contribute genetic material to their offspring, each child carries two copies of almost every gene, one from each parent. For some diseases to occur, both copies must be flawed. Such diseases are called autosomal recessive diseases. Some forms of LGMD and DD exhibit this pattern of inheritance, as does CMD. A person with only one flawed copy, called a carrier, will not have the disease, but may pass the flawed gene on to his children. When two carriers have children, the chances of having a child with the disease is one in four for each pregnancy.
Other diseases occur when only one flawed gene copy is present. Such diseases are called autosomal dominant diseases. Other forms of LGMD exhibit this pattern of inheritance, as do DM, FSH, OPMD, and some forms of DD. When a person affected by the disease has a child with someone not affected, the chances of having an affected child is one in two.
Because of chromosomal differences between the sexes, some genes are not present in two copies. The chromosomes that determine whether a person is male or female are called the X and Y chromosomes. A person with two X chromosomes is female, while a person with one X and one Y is male. While the X chromosome carries many genes, the Y chromosome carries almost none. Therefore, a male has only one copy of each gene on the X chromosome, and if it is flawed, he will have the disease that defect causes. Such diseases are said to be X-linked. X-linked diseases include DMD, BMD, and EDMD. Women aren't usually affected by X-linked diseases, since they will likely have one unaffected copy between the two chromosomes. Some female carriers of DMD suffer a mild form of the disease, probably because their one unaffected gene copy is shut down in some of their cells.
Women carriers of X-linked diseases have a one in two chance of passing the flawed gene on to each child born. Daughters who inherit the disease gene will be carriers. A son born without the disease gene will be free of the disease and cannot pass it on to his children. A son born with the defect will have the disease. He will pass the flawed gene on to each of his daughters, who will then be carriers, but to none of his sons (because they inherit his Y chromosome).
Not all genetic flaws are inherited. As many as one third of the cases of DMD are due to new mutations that arise during egg formation in the mother. New mutations are less common in other forms of muscular dystrophy.

Symptoms

All of the muscular dystrophies are marked by muscle weakness as the major symptom. The distribution of symptoms, age of onset, and progression differ significantly. Pain is sometimes a symptom of each, usually due to the effects of weakness on joint position.
DMD. A boy with Duchenne muscular dystrophy usually begins to show symptoms as a pre-schooler. The legs are affected first, making walking difficult and causing balance problems. Most patients walk three to six months later than expected and have difficulty running. Later on, the boy with DMD will push his hands against his knees to rise to a standing position, to compensate for leg weakness. About the same time, his calves will begin to swell, though with fibrous tissue rather than with muscle, and feel firm and rubbery; this condition gives DMD one of its alternate names, pseudohypertrophic muscular dystrophy. He will widen his stance to maintain balance, and walk with a waddling gait to advance his weakened legs. Contractures (permanent muscle tightening) usually begin by age five or six, most severely in the calf muscles. This pulls the foot down and back, forcing the boy to walk on tip-toes, called equinus, and further decreases balance. Frequent falls and broken bones are common beginning at this age. Climbing stairs and rising unaided may become impossible by age nine or ten, and most boys use a wheelchair for mobility by the age of 12. Weakening of the trunk muscles around this age often leads to scoliosis (a side-to-side spine curvature) and kyphosis (a front-to-back curvature).
The most serious weakness of DMD is weakness of the diaphragm, the sheet of muscles at the top of the abdomen that perform the main work of breathing and coughing. Diaphragm weakness leads to reduced energy and stamina, and increased lung infection because of the inability to cough effectively. Young men with DMD often live into their twenties and beyond, provided they have mechanical ventilation assistance and good respiratory hygiene.
About one third of boys with DMD experience specific learning disabilities, including trouble learning by ear rather than by sight and trouble paying attention to long lists of instructions. Individualized educational programs usually compensate well for these disabilities.
BMD. The symptoms of BMD usually appear in late childhood to early adulthood. Though the progression of symptoms may parallel that of DMD, the symptoms are usually milder and the course more variable. The same pattern of leg weakness, unsteadiness, and contractures occur later for the young man with BMD, often allowing independent walking into the twenties or early thirties. Scoliosis may occur, but is usually milder and progresses more slowly. Heart muscle disease (cardiomyopathy), occurs more commonly in BMD. Problems may include irregular heartbeats (arrhythmias) and congestive heart failure. Symptoms may include fatigue, shortness of breath, chest pain, and dizziness. Respiratory weakness also occurs, and may lead to the need for mechanical ventilation.
EDMD. This type of muscular dystrophy usually begins in early childhood, often with contractures preceding muscle weakness. Weakness affects the shoulder and upper arm originally, along with the calf muscles, leading to foot-drop. Most men with EDMD survive into middle age, although a defect in the heart's rhythm (heart block) may be fatal if not treated with a pacemaker.
LGMD. While there are at least a half-dozen genes that cause the various types of LGMD, two major clinical forms of LGMD are usually recognized. A severe childhood form is similar in appearance to DMD, but is inherited as an autosomal recessive trait. Symptoms of adult-onset LGMD usually appear in a person's teens or twenties, and are marked by progressive weakness and wasting of the muscles closest to the trunk. Contractures may occur, and the ability to walk is usually lost about 20 years after onset. Some people with LGMD develop respiratory weakness that requires use of a ventilator. Lifespan may be somewhat shortened. (Autosomal dominant forms usually occur later in life and progress relatively slowly.)
FSH. FSH varies in its severity and age of onset, even among members of the same family. Symptoms most commonly begin in the teens or early twenties, though infant or childhood onset is possible. Symptoms tend to be more severe in those with earlier onset. The disease is named for the regions of the body most severely affected by the disease: muscles of the face (facio-), shoulders (scapulo-), and upper arms (humeral). Hips and legs may be affected as well. Children with FSH often develop partial or complete deafness.
The first symptom noticed is often difficulty lifting objects above the shoulders. The weakness may be greater on one side than the other. Shoulder weakness also causes the shoulder blades to jut backward, called scapular winging. Muscles in the upper arm often lose bulk sooner than those of the forearm, giving a "Popeye" appearance to the arms. Facial weakness may lead to loss of facial expression, difficulty closing the eyes completely, and inability to drink through a straw, blow up a balloon, or whistle. A person with FSH may not develop strong facial wrinkles. Contracture of the calf muscles may cause foot-drop, leading to frequent tripping over curbs or rough spots. People with earlier onset often require a wheelchair for mobility, while those with later onset rarely do.
MYOTONIC DYSTROPHY. Symptoms of Myotonic dystrophy include facial weakness and a slack jaw, drooping eyelids (ptosis), and muscle wasting in the forearms and calves. A person with this dystrophy has difficulty relaxing his grasp, especially if the object is cold. Myotonic dystrophy affects heart muscle, causing arrhythmias and heart block, and the muscles of the digestive system, leading to motility disorders and constipation. Other body systems are affected as well: Myotonic dystrophy may cause cataracts, retinal degeneration, low IQ, frontal balding, skin disorders, testicular atrophy, sleep apnea, and insulin resistance. An increased need or desire for sleep is common, as is diminished motivation. Severe disability affects most people with this type of dystrophy within 20 years of onset, although most do not require a wheelchair even late in life.
OPMD. OPMD usually begins in a person's thirties or forties, with weakness in the muscles controlling the eyes and throat. Symptoms include drooping eyelids, difficulty swallowing (dysphagia), and weakness progresses to other muscles of the face, neck, and occasionally the upper limbs. Swallowing difficulty may cause aspiration, or the introduction of food or saliva into the airways. Pneumonia may follow.
DD. DD usually begins in the twenties or thirties, with weakness in the hands, forearms, and lower legs. Difficulty with fine movements such as typing or fastening buttons may be the first symptoms. Symptoms progress slowly, and the disease usually does not affect life span.
CMD. CMD is marked by severe muscle weakness from birth, with infants displaying "floppiness" and very little voluntary movement. Nonetheless, a child with CMD may learn to walk, either with or without some assistive device, and live into young adulthood or beyond. In contrast, children with Fukuyama CMD are rarely able to walk, and have severe mental retardation. Most children with this type of CMD die in childhood.

Diagnosis

Diagnosis of muscular dystrophy involves a careful medical history and a thorough physical exam to determine the distribution of symptoms and to rule out other causes. Family history may give important clues, since all the muscular dystrophies are genetic conditions (though no family history will be evident in the event of new mutations).
Lab tests may include:
  • Blood level of the muscle enzyme creatine kinase (CK). CK levels rise in the blood due to muscle damage, and may be seen in some conditions even before symptoms appear.
  • Muscle biopsy, in which a small piece of muscle tissue is removed for microscopic examination. Changes in the structure of muscle cells and presence of fibrous tissue or other aberrant structures are characteristic of different forms of muscular dystrophy. The muscle tissue can also be stained to detect the presence or absence of particular proteins, including dystrophin.
  • Electromyogram (EMG). This electrical test is used to examine the response of the muscles to stimulation. Decreased response is seen in muscular dystrophy. Other characteristic changes are seen in DM.
  • Genetic tests. Several of the muscular dystrophies can be positively identified by testing for the presence of the mutated gene involved. Accurate genetic tests are available for DMD, BMD, DM, several forms of LGMD, and EDMD.
  • Other specific tests as necessary. For EDMD and BMD, for example, an electrocardiogram may be needed to test heart function, and hearing tests are performed for children with FSH.
For most forms of muscular dystrophy, accurate diagnosis is not difficult when done by someone familiar with the range of diseases. There are exceptions, however. Even with a muscle biopsy, it may be difficult to distinguish between FSH and another muscle disease, polymyositis. Childhood-onset LGMD is often mistaken for the much more common DMD, especially when it occurs in boys. BMD with an early onset appears very similar to DMD, and a genetic test may be needed to accurately distinguish them. The muscular dystrophies may be confused with diseases involving the motor neurons, such as spinal muscular atrophy; diseases of the neuromuscular junction, such as myasthenia gravis; and other muscle diseases, as all involve generalized weakening of varying distribution.

Treatment

Drugs

There are no cures for any of the muscular dystrophies. Prednisone, a corticosteroid, has been shown to delay the progression of DMD somewhat, for reasons that are still unclear. Prednisone is also prescribed for BMD, though no controlled studies have tested its benefit. A related drug, deflazacort, appears to have similar benefits with fewer side effects. It is available and is prescribed in Canada and Mexico, but is unavailable in the United States. Albuterol, an adrenergic agonist, has shown some promise for FSH in small trials; larger trials are scheduled for 1998. No other drugs are currently known to have an effect on the course of any other muscular dystrophy.
Treatment of muscular dystrophy is mainly directed at preventing the complications of weakness, including decreased mobility and dexterity, contractures, scoliosis, heart defects, and respiratory insufficiency.

Physical therapy

Physical therapy, in particular regular stretching, is used to maintain the range of motion of affected muscles and to prevent or delay contractures. Braces are used as well, especially on the ankles and feet to prevent equinus. Full-leg braces may be used in DMD to prolong the period of independent walking. Strengthening other muscle groups to compensate for weakness may be possible if the affected muscles are few and isolated, as in the earlier stages of the milder muscular dystrophies. Regular, nonstrenuous exercise helps maintain general good health. Strenuous exercise is usually not recommended, since it may damage muscles further.

Surgery

When contractures become more pronounced, tenotomy surgery may be performed. In this operation, the tendon of the contractured muscle is cut, and the limb is braced in its normal resting position while the tendon regrows. In FSH, surgical fixation of the scapula can help compensate for shoulder weakness. For a person with OPMD, surgical lifting of the eyelids may help compensate for weakened muscular control. For a person with DM, sleep apnea may be treated surgically to maintain an open airway. Scoliosis surgery is often needed in DMD, but much less often in other muscular dystrophies. Surgery is recommended at a much lower degree of curvature for DMD than for scoliosis due to other conditions, since the decline in respiratory function in DMD makes surgery at a later time dangerous. In this surgery, the vertebrae are fused together to maintain the spine in the upright position. Steel rods are inserted at the time of operation to keep the spine rigid while the bones grow together.
When any type of surgery is performed in patients with muscular dystrophy, anesthesia must be carefully selected. People with MD are susceptible to a severe reaction, known as malignant hyperthermia, when given halothane anesthetic.

Occupational therapy

The occupational therapist suggests techniques and tools to compensate for the loss of strength and dexterity. Strategies may include modifications in the home, adaptive utensils and dressing aids, compensatory movements and positioning, wheelchair accessories, or communication aids.

Nutrition

Good nutrition helps to promote general health in all the muscular dystrophies. No special diet or supplement has been shown to be of use in any of the conditions. The weakness in the throat muscles seen especially in OPMD and later DMD may necessitate the use of a gastrostomy tube, inserted in the stomach to provide nutrition directly.

Cardiac care

The arrhythmias of EDMD and BMD may be treatable with antiarrhythmia drugs such as mexiletine or nifedipine. A pacemaker may be implanted if these do not provide adequate control. Heart transplants are increasingly common for men with BMD.

Respiratory care

People who develop weakness of the diaphragm or other ventilatory muscles may require a mechanical ventilator to continue breathing deeply enough. Air may be administered through a nasal mask or mouthpiece, or through a tracheostomy tube, which is inserted through a surgical incision through the neck and into the windpipe. Most people with muscular dystrophy do not need a tracheostomy, although some may prefer it to continual use of a mask or mouthpiece. Supplemental oxygen is not needed. Good hygiene of the lungs is critical for health and longterm survival of a person with weakened ventilatory muscles. Assisted cough techniques provide the strength needed to clear the airways of secretions; an assisted cough machine is also available and provides excellent results.

Experimental treatments

Two experimental procedures aiming to cure DMD have attracted a great deal of attention in the past decade. In myoblast transfer, millions of immature muscle cells are injected into an affected muscle. The goal of the treatment is to promote the growth of the injected cells, replacing the defective host cells with healthy new ones. Despite continued claims to the contrary by a very few researchers, this procedure is widely judged a failure. Modifications in the technique may change that in the future.
Gene therapy introduces good copies of the dystrophin gene into muscle cells. The goal is to allow the existing muscle cells to use the new gene to produce the dystrophin it cannot make with its flawed gene. Problems have included immune rejection of the virus used to introduce the gene, loss of gene function after several weeks, and an inability to get the gene to enough cells to make a functional difference in the affected muscle. Nonetheless, after a number of years of refining the techniques in mice, researchers are beginning human trials in 1998.

Prognosis

The expected lifespan for a male with DMD has increased significantly in the past two decades. Most young men will live into their early or mid-twenties. Respiratory infections become an increasing problem as their breathing becomes weaker, and these infections are usually the cause of death.
The course of the other muscular dystrophies is more variable; expected life spans and degrees of disability are hard to predict, but may be related to age of onset and initial symptoms. Prediction is made more difficult because, as new genes are discovered, it is becoming clear that several of the dystrophies are not uniform disorders, but rather symptom groups caused by different genes.
People with dystrophies with significant heart involvement (BMD, EDMD, Myotonic dystrophy) may nonetheless have almost normal life spans, provided that cardiac complications are monitored and treated aggressively. The respiratory involvement of BMD and LGMD similarly require careful and prompt treatment.

Prevention

There is no way to prevent any of the muscular dystrophies in a person who has the genes responsible for these disorders. Accurate genetic tests, including prenatal tests, are available for some of the muscular dystrophies. Results of these tests may be useful for purposes of family planning.

Resources

Organizations

Muscular Dystrophy Association. 3300 East Sunrise Drive, Tucson, AZ 85718. (800) 572-1717. http://www.mdausa.org.

Key terms

Autosomal dominant — Diseases that occur when a person inherits only one flawed copy of the gene.
Autosomal recessive — Diseases that occur when a person inherits two flawed copies of a gene—one from each parent.
Becker muscular dystrophy (BMD) — A type of muscular dystrophy that affects older boys and men, and usually follows a milder course than DMD.
Contractures — A permanent shortening (as of muscle, tendon, or scar tissue) producing deformity or distortion.
Distal muscular dystrophy (DD) — A form of muscular dystrophy that usually begins in middle age or later, causing weakness in the muscles of the feet and hands.
Duchenne muscular dystrophy (DMD) — The most severe form of muscular dystrophy, DMD usually affects young boys and causes progressive muscle weakness, usually beginning in the legs.
Dystrophin — A protein that helps muscle tissue repair itself. Both DMD and BMD are caused by flaws in the gene that instructs the body how to make this protein.
Facioscapulohumeral muscular dystrophy (FSH) — This form of muscular dystrophy, also known as Landouzy-Dejerine disease, begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles of the face, shoulders, and upper arms.
Limb-girdle muscular dystrophy (LGMD) — This form of muscular dystrophy begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles around the hips and shoulders.
Myotonic dystrophy — This type of muscular dystrophy, also known as Steinert's disease, affects both men and women, causing generalized weakness first seen in the face, feet, and hands. It is accompanied by the inability to relax the affected muscles (myotonia).
Oculopharyngeal muscular dystrophy (OPMD) — This type of muscular dystrophy affects adults of both sexes, causing weakness in the eye muscles and throat.

dystrophy

 [dis´trah-fe]
any disorder due to defective or faulty nutrition, especially muscular dystrophy. adj., adj dystroph´ic.
adiposogenital dystrophy adiposity of the feminine type, genital hypoplasia, changes in secondary sex characters, and metabolic disturbances; seen with lesions of the hypothalamus; see also adiposogenital dystrophy.
Becker's muscular dystrophy (Becker type muscular dystrophy) a form closely resembling Duchenne's muscular dystrophy, but having a later onset and milder course; transmitted as an X-linked recessive trait.
distal muscular dystrophy distal myopathy.
Duchenne's muscular dystrophy (Duchenne type muscular dystrophy) The childhood type of muscular dystrophy.
facioscapulohumeral muscular dystrophy muscular dystrophy affecting the face, shoulder, and upper arm muscles; called also Landouzy-Dejerine muscular dystrophy.
Landouzy-Dejerine dystrophy (Landouzy-Dejerine muscular dystrophy) facioscapulohumeral muscular dystrophy.
muscular dystrophy see muscular dystrophy.
myotonic dystrophy a rare, slowly progressive, hereditary disease, marked by myotonia followed by muscular atrophy (especially of the face and neck), cataracts, hypogonadism, frontal balding, and cardiac disorders. Called also dystrophia myotonica, myotonia atrophica, and myotonia dystrophica.
progressive muscular dystrophy muscular dystrophy.
pseudohypertrophic muscular dystrophy muscular dystrophy affecting the shoulder and pelvic girdles, beginning in childhood and marked by increasing weakness, pseudohypertrophy of the muscles, followed by atrophy, and a peculiar swaying gait with the legs kept wide apart. Called also pseudohypertrophic muscular paralysis.
reflex sympathetic dystrophy a syndrome of chronic pain that usually develops after a trauma or noxious stimulus, although the nerve injury cannot be immediately identified. The pain is not limited to the distribution of a single nerve and is often out of proportion to the precipitating event. It is most often described as a burning pain, and is accompanied by swelling, sweating, sensitivity to touch, and sometimes changes in tissue growth. Called also chronic or complex regional pain syndrome. Clinical practice guidelines have been published by the Reflex Sympathetic Dystrophy Syndrome Association of America and are available on their web site at http://www.rsds.org or by writing to Reflex Sympathetic Dystrophy Syndrome Association of America, P.O. Box 502, Milford CT 06460.

muscular

 [mus´ku-lar]
1. pertaining to a muscle.
2. having well-developed muscles.
muscular dystrophy a group of genetically determined, painless, degenerative myopathies that are progressively crippling because muscles are gradually weakened and eventually atrophy. At present there is no specific cure. Not all forms are totally disabling, and it can sometimes be arrested temporarily.

The word dystrophy means faulty or imperfect nutrition. In muscular dystrophy the muscles suffer a vital loss of protein, and muscle fibers are replaced gradually by fat and connective tissue until, in the late stages of the disease, the voluntary muscle system becomes virtually useless. In muscular dystrophy all visible damage occurs in the muscles themselves, and thus the disease is markedly different from multiple sclerosis, in which the muscles are rendered impotent by damage to the nerves that control them.

Muscular dystrophy is believed to be hereditary, although the way it is inherited is not the same for all types of the disease. The disease (or a propensity for it) seems to be carried mainly by women who, while not suffering from it themselves, may pass it on to their offspring, usually their sons. A woman who has conceived a child with muscular dystrophy is probably a carrier, as is a woman who has a relative with the condition.
Childhood Muscular Dystrophy. Muscular dystrophy cannot be detected at birth; in most cases symptoms begin to be noticeable about the second or third year. The child gradually finds it more difficult to play and walk, and as the weakening process continues, a wheelchair becomes necessary. In many cases death comes before the age of 20 from respiratory ailments or heart failure. This childhood type of disease (unfortunately the most common type) is known as the Duchenne type or progressive muscular dystrophy. It is also called pseudohypertrophic muscular dystrophy because at the beginning the muscles, especially those in the calves, appear healthy and bulging when actually they are already weakened and their size is due to an excess of fat.
Other Types. Another type sometimes begins in childhood but is much more likely to appear during the teens or twenties. When the first symptom is a failure of the musculature of the pelvic girdle, this type is referred to as limb-girdle muscular dystrophy. It usually proceeds more slowly than the childhood form. This same type may take the form of facioscapulohumeral muscular dystrophy (referring to the face, shoulder, and upper arm muscles), which is likely to manifest itself first in an almost imperceptible weakening of the facial muscles. It is also known as Landouzy-Dejerine muscular dystrophy. Muscle deterioration starts in childhood or early adulthood but it may proceed very gradually over a number of years, sometimes until late in life. Some patients may be only slightly disabled.

Other, rarer types of muscular dystrophy have been identified, including a distal type that begins in the peripheral muscles of the extremities and one that affects only muscles of the eye. Sometimes two or more forms are present in the same patient.
Management. There is almost never any pain in muscular dystrophy. The mind is not affected; patients have normal intelligence. As the small muscles often are the last to be damaged, patients may continue to use their fingers. Children with muscular dystrophy are able to enjoy many recreations, even when they must rely on crutches or wheelchairs. Physical therapy, including exercise of the lungs by deep breathing, is important. The aim of such exercise is not to restore muscle power (which cannot be done) but to ensure that the patient makes the best use of the good muscle tissue remaining and does not develop contractures. The more active patients are, the better they will be physically and mentally. Obesity should be avoided. Splints, braces, and, occasionally, corrective orthopedic surgery are sometimes helpful.

The Muscular Dystrophy Association of America has many local chapters and is concerned both with research and with every aspect of the care and comfort of patients with the disease. They can be contacted at Muscular Dystrophy Association of America, 3300 East Sunrise Drive, Tucson, AZ 85718, or through their web site at http://www.mdausa.org. The Muscular Dystrophy Association of Canada also has information available and has many local chapters. Their national office can be contacted by writing to Muscular Dystrophy Association of Canada, 2345 Yonge Street, Suite 900, Toronto ON M4P 2E5 or consulting their web site at http://www.mdac.ca.

mus·cu·lar dys·tro·phy

a general term for a number of hereditary, progressive degenerative disorders affecting skeletal muscles, and often other organ systems.

muscular dystrophy

n. Abbr. MD
Any of a group of progressive muscle disorders caused by a defect in one or more genes that control muscle function and characterized by gradual irreversible wasting of skeletal muscle.

muscular dystrophy (MD)

Etymology: L, musculus + Gk, dys, bad, trophe, nourishment
a group of genetically transmitted diseases characterized by progressive atrophy of symmetric groups of skeletal muscles without evidence of involvement or degeneration of neural tissue. In all forms of muscular dystrophy an insidious loss of strength with increasing disability and deformity occurs, although each type differs in the groups of muscles affected, the age of onset, the rate of progression, and the mode of genetic inheritance. The basic cause is unknown but appears to be an inborn error of metabolism. Serum creatine phosphokinase level is increased in affected individuals and acts as a diagnostic aid, especially in asymptomatic children in families at risk. Diagnostic confirmation is made by muscle biopsy, electromyography, and genetic pedigree. Treatment of the muscular dystrophies consists primarily of supportive measures, such as physical therapy and orthopedic procedures to minimize deformity. The main types of the disease are pseudohypertrophic (Duchenne's muscular dystrophy), limb-girdle muscular dystrophy, and facioscapulohumeral muscular dystrophy. Rarer forms include Becker's muscular dystrophy, distal muscular dystrophy, ocular myopathy, and myotonic muscular dystrophy. Also called myodystrophy. See also myotonic myopathy.

muscular dystrophy

Inherited myopathy Neurology Any of the primary degenerative myopathies, characterized by selective atrophy and weakness of voluntary muscles, pseudohypertrophy–see Champagne bottle legs, progressive deterioration, and early death; usually X-linked, often recessive. , also AD and AR, affecting 1:3500 ♂ children, the most common form of which, Duchenne's muscular dystrophy, is fatal by age 20.
Muscular dystrophy, short classification  
Name/Heredity Location Onset/death
Becker/ X-R Pelvifemoral 15-20/50-60
Duchenne/ X-R Pelvifemoral 20-50/ ±20
Erb/AR Scapula 20-30
Landouzy-Dejerine/AD  Facioscapulohumeral 15-30/benign
Leyden-Mobius/AR  Pelvic girdle  20-50/ ±20
AD Autosomal dominant; AR Autosomal recessive; X-R X-linked recessive

mus·cu·lar dys·tro·phy

(MD) (mŭs'kyū-lăr dis'trŏ-fē)
A general term for various hereditary, progressive degenerative disorders affecting skeletal muscles, and often other organ systems as well.
Synonym(s): myodystrophy, myodystrophia.

muscular dystrophy

One of a group of hereditary muscle disorders that feature gradual, progressive muscle degeneration leading to increasing weakness and disability. Duchenne dystrophy is a RECESSIVE sex-linked condition and is thus almost confined to males. It affects first the leg and buttock muscles and progresses usually to a fatal outcome in the mid-teens. The muscles appear bulkier than normal (pseudohypertrophy). The limb girdle type of dystrophy has a recessive inheritance and affects initially the shoulder and hip muscles. It usually causes severe disability within about 20 years. The facio-scapulo-humeral type has a dominant inheritance and weakens the muscles of the face, upper back and upper arm. It progresses very slowly and does not necessarily shorten life. There is no known treatment for muscular dystrophy. See also DYSTROPHIN.

muscular dystrophy (MD)

a disease characterized by the progressive wasting of muscles and eventual death. One type, called Duchenne MD, is controlled by a recessive sex-linked gene (see SEX LINKAGE) and, as a result, affects more boys than girls. The disease first shows itself between one and six years, progressing until the patient is confined to a wheelchair by the early teens with death resulting by the late teens in most affected individuals. Other forms of M.D. are controlled by autosomal genes (both dominant and recessive) and they are equally frequent in males and females.
muscular dystrophy inborn muscle tissue dysfunction

muscular dystrophy (musˑ·ky·ler disˈ·tr·fē),

n umbrella term for a group of genetically inherited diseases characterized by gradual atrophy of skeletal muscles without any neurologic damage.

mus·cu·lar dys·tro·phy

(mŭs'kyū-lăr dis'trŏ-fē)
General term for hereditary progressive degenerative disorders affecting skeletal muscles and other organ systems.

muscular dystrophy (mus´kūlur dis´trōfē),

n a group of genetically transmitted diseases characterized by progressive atrophy of symmetric groups of skeletal muscles without evidence of involvement or degeneration of neural tissue. In all forms of muscular dystrophy there is an insidious loss of strength with increasing disability and deformity. Serum creatine phosphokinase is increased in affected individuals and acts as a diagnostic aid. Diagnosis is confirmed by muscle biopsy, electromyography, and genetic pedigree.
muscular dystrophy, Duchenne
n.pr a genetic myopathic condition distinguished by the enlarged size of specific muscles (e.g., calves), noticeable indications of lordosis accompanied by a swelling of the abdominal region; diminished capacity to stand, walk, and maintain balance; a progressive deterioration of the muscles; and limited intellectual development.
muscular dystrophy, facioscapulohu-meral
(fā´shēōskap´ūlōhyoo´mərəl),
n a genetic myopathic condition involving the facial muscles and distinguished by prominent scapula, weak muscles of the shoulders, and marked difficulty in lifting the arms and completely shutting the eyes.

dystrophy

any disorder due to defective or faulty nutrition. See also corneal dystrophy, muscular dystrophy.

Duchenne dystrophy
see Duchenne muscular dystrophy.
muscular dystrophy
includes enzootic muscular dystrophy of cattle, sheep, pigs and foals, all of dietary origin, and some probably familial diseases in cattle, sheep and dogs. See also muscular dystrophy.

muscular

1. pertaining to a muscle.
2. having well developed muscles.

muscular asymmetry
due usually to neuronal or disuse atrophy on one side of the body.
muscular atrophy
wasting away of muscle or a muscle because of reduction in cross sectional area of muscle fibers; may be due to disease of the muscle or its nerve supply, or to disuse or nutritional inadequacy. See also hereditary spinal muscular atrophy (below).
muscular degeneration
varies in severity from degeneration of only the myofibrils or degeneration of the myofibrils plus sarcoplasm, leaving satellite cells and myonuclei and sarcolemmal laminae unaffected, or further levels of increasing severity.
muscular denervation
destruction or congenital absence of the motor nerve supply to the muscle; manifested by paralysis and atrophy and absence of spinal reflexes.
muscular denervation atrophy
progressive shrinkage of muscle fibers when the nerve supply to the muscle is severed.
Duchenne muscular dystrophy
an X-linked inherited disease in humans, which is believed to be due to a deficiency of a membrane-associated protein, dystrophin. An analogous disease has been identified in Irish terriers, Golden retrievers and mice.
muscular dystrophy
any degenerative muscular disorder due to faulty nutrition of the muscles. Causes muscle weakness, liberation of myoglobin into the circulation from skeletal muscle and subsequent wasting and possible contracture. In humans there are a group of genetically determined, painless, degenerative myopathies that are progressively crippling because muscles are gradually weakened and eventually atrophy. In food animals the principal disease in this group is enzootic muscular dystrophy caused by a nutritional deficiency of selenium and/or vitamin E. Sporadic cases of muscular dystrophy of unknown etiology occur rarely in dogs.
muscular fascicle
muscular fasciculation
muscular fatigue
during brief, intense exercise probably due in large part to the accumulation of lactate.
hereditary spinal muscular atrophy
progressive degeneration of the motor cells of the spinal cord. It is an inherited, slowly progressive flaccid tetraparesis from an early age, with muscular atrophy. Occurs as an autosomal recessive trait in Swedish lapland dogs, a dominant trait in Brittany spaniels. Also reported in German shepherd dogs, English pointers and Rottweilers. See also hereditary neuronal abiotrophy of Swedish Lapland dogs. In cattle, inherited as an autosomal recessive trait and reported in Brown Swiss, Holstein-Friesian and Red Danish calves with an onset at 3 to 8 weeks of age. There is hind limb ataxia progressing to recumbancy. Associated with lesions in the lower motor neurons of the cervical and lumbar spinal cord.
muscular hernia
hernia through an enclosing muscle sheath.
muscular hyperplasia
an increase in the size of a muscle mass due to an increase in the number of muscle cells. See also myofiber hyperplasia, ileal muscular hypertrophy.
muscular hypertrophy
an increase in the size of a muscle mass due to an increase in the length and thickness of each muscle cell without any increase in the number of cells.
muscular ischemia
short duration or temporary or partial cessation of blood supply causes loss of muscle power and possibly some muscle fiber necrosis; long duration or severe or complete cessation cause ischemic muscle necrosis and atrophy. See also compartment syndrome, downer cow syndrome.
muscular ischemic necrosis
see ischemic myonecrosis.
muscular mineralization
ectopic deposition of minerals in muscle. See mineralization.
myelopathic muscular atrophy
muscular atrophy due to a lesion of the spinal cord, as in spinal muscular atrophy.
nutritional muscular dystrophy
see muscular dystrophy (above).
muscular parasitic diseases
includes cysticercosis, hepatozoonosis, Neosprum caninum myositis, sarcocystosis, toxoplasmosis, trichenellosis.
muscular receptors
muscle spindles which respond to stretch.
muscular steatosis
excess fat deposits in muscle; a problem only at meat hygiene inspection.
muscular vascular occlusive syndrome
see ischemic myonecrosis.
muscular weakness
X-linked muscular dystrophy
see Duchenne muscular dystrophy (above).
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