What is Muscular Dystrophy?
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This condition is a group of inherited muscle diseases in which muscle fibers are unusually susceptible to damage. Muscles, primarily voluntary muscles, become progressively weaker. In the late stages of muscular dystrophy, fat and connective tissue often replace muscle fibers.
Some types of MD affect heart muscles, other involuntary muscles and other organs.
The most common types of the affliction appear to be due to a genetic deficiency of the muscle protein dystrophin.
Nine types of muscular dystrophies are generally recognized.
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.
Muscular dystrophy is a general term for a group of inherited diseases involving a defective gene. Each form of muscular dystrophy is caused by a genetic mutation that's particular to that type of the disease. The most common types of muscular dystrophy appear to be due to a genetic deficiency of the muscle protein dystrophin.
Inheriting Duchenne's or Becker's MD
Duchenne's and Becker's muscular dystrophies are passed from mother to son through one of the mother's genes in a pattern called X-linked recessive inheritance. Boys inherit an X chromosome from their mothers and a Y chromosome from their fathers. The X-Y combination makes them male. Girls inherit two X chromosomes, one from their mothers and one from their fathers. The X-X combination determines that they are female.
The defective gene that causes Duchenne's and Becker's muscular dystrophies is located on the X-chromosome. Women who have only one X-chromosome with the defective gene that causes these muscular dystrophies are carriers and sometimes develop heart muscle problems (cardiomyopathy) and mild muscle weakness.
The disease can skip a generation until another son inherits the defective gene on the X-chromosome. In some cases of Duchenne's and Becker's muscular dystrophies, the disease arises from a new mutation in a gene rather than from an inherited defective gene.
Patterns differ for other types of MD
Myotonic dystrophy is passed along in a pattern called autosomal dominant inheritance. If either parent carries the defective gene for myotonic dystrophy, there's a 50 percent chance the disorder will be passed along to a child.
Some of the less common types of muscular dystrophy are passed along in the same inheritance pattern that marks Duchenne's and Becker's muscular dystrophies. Other types of muscular dystrophy can be passed on from generation to generation and affect males and females equally. Still others require a defective gene from both parents.
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.
Signs and symptoms vary according to the type of muscular dystrophy. In general, muscular dystrophy symptoms may include:
Muscle weakness Apparent lack of coordination Progressive crippling, resulting in fixations (contractures) of the muscles around your joints and loss of mobility
Many specific signs and symptoms vary from among the different forms of MD. Each type is different in the age of onset, which parts of the body the symptoms primarily affect and how rapidly the disease progresses.
These types of muscular dystrophies are due to a genetic defect of the protein dystrophin.
Duchenne's muscular dystrophy is the most severe form of dystrophinopathy. It occurs mostly in young boys and is the most common form of MD that affects children. Signs and symptoms of Duchenne's MD may include:
Frequent falls Large calf muscles Difficulty getting up from a lying or sitting position Weakness in lower leg muscles, resulting in difficulty running and jumping Waddling gait Mild mental retardation, in some cases
Signs and symptoms of Duchenne's usually appear between the ages of 2 and 6. It first affects the muscles of the pelvis, upper arms and upper legs. By late childhood, most children with this form of muscular dystrophy are unable to walk.
Most die by their late teens or early 20s, often from pneumonia, respiratory muscle weakness or cardiac complications. Some people with Duchenne's MD may exhibit curvature of their spine (scoliosis).
Becker's muscular dystrophy is a milder form of dystrophinopathy. It generally affects older boys and young men, and progresses more slowly, usually over several decades. Signs and symptoms of Becker's MD are similar to those of Duchenne's.
The onset of the signs and symptoms is generally around age 11, but may not occur until the mid-20s or even later. Those affected by Becker's MD usually are able to walk through their teens, and often well into adulthood.
Also known as Steinert's disease, this form of muscular dystrophy produces stiffness of muscles and an inability to relax muscles at will (myotonia), as well as the muscle weakness of the other forms of muscular dystrophy.
Although this form of MD can affect children, it often doesn't affect people until adulthood. It can vary greatly in its severity. Muscles may feel stiff after using them. Progression of this form of MD is slow. Besides myotonia, signs and symptoms of adult-onset myotonic dystrophy may include:
Weakening of voluntary muscles that control your arms and legs, usually beginning with the limb muscles farthest from the torso — the muscles of the feet, hands, lower legs and forearms.
Weakening of head, neck and face muscles, which may result in the face having a hollow, drooped appearance.
Weakening of muscles involved in breathing and swallowing. Weaker breathing muscles may result in less oxygen intake and fatigue. Weaker swallowing muscles increase the risk of choking.
Fainting or dizziness, which may indicate that the disease is interfering with the conduction of electrical signals that keep the heart rate normal.
Weakening of muscles of hollow internal organs such as those in the digestive tract and the uterus. Depending on which part of the digestive tract is affected, you may experience problems with swallowing as well as constipation and diarrhea. Weakness of the uterine walls may cause problems during childbirth.
Difficulty sleeping well at night and daytime sleepiness, and inability to concentrate because of the effect of the disease on the brain.
Frontal balding in men.
Clouding of the lenses of the eyes (cataracts).
Rarely, infants have this form of muscular dystrophy, in which case it's called congenital myotonic dystrophy. The infant form is more severe, although infants with myotonic dystrophy don't experience myotonia. Signs in infants may include:
Severe muscle weakness Difficulty sucking and swallowing Difficulty breathing Cognitive impairment
Facioscapulohumeral muscular dystrophy
Also known as Landouzy-Dejerine dystrophy, this form involves progressive muscle weakness, usually in this order:
Face Shoulders Abdomen Feet Upper arms Pelvic area Lower arms
When someone with facioscapulohumeral MD raises his or her arms, the shoulder blades may stick out like wings. Progression of this form is slow, with some spurts of rapidly increasing weakness. Onset usually occurs during the teen to early adult years.
Other major types of muscular dystrophy
The other major types of muscular dystrophy include:
Limb-girdle muscular dystrophy Congenital muscular dystrophy Oculopharyngeal muscular dystrophy Distal muscular dystrophy Emery-Dreifuss muscular dystrophy
Limb-girdle muscular dystrophy
Muscles usually affected first by this form of muscular dystrophy include:
This form then progresses to the arms and legs, though progression is slow. Limb-girdle MD may begin from early childhood to adulthood.
Congenital muscular dystrophy
Signs of congenital MD may include:
General muscle weakness Joint deformities
This form is apparent at birth and progresses slowly. More severe forms of congenital MDs may involve severe mental and speech problems as well as seizures.
Oculopharyngeal muscular dystrophy
The first sign of this type of muscular dystrophy is usually drooping of the eyelids, followed by weakness of the muscles of the eye, face and throat, resulting in difficulty swallowing. Progression is slow. Signs and symptoms first appear in adulthood, usually in a person's 40s or 50s.
Distal muscular dystrophy
This group involves the muscles farthest away from the center of the body — those of the hands, forearms, feet and lower legs. The severity is generally less than for other forms of MD, and this form tends to progress slowly. Distal MD generally begins in adulthood between the ages of 40 and 60.
Emery-Dreifuss muscular dystrophy
This form of muscular dystrophy usually begins in the muscles of the:
Shoulders Upper arms Shins
Cardiac arrhythmias, stiffness of the spine and muscle contractures are other features of Emery-Dreifuss MD. Emery-Dreifuss MD usually begins in the childhood to early teen years and progresses slowly.
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.
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.
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.
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.
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 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.
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 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 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 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.
Duchenne's muscular dystrophy occurs almost exclusively in boys, although it can occur in girls. Your young child may have difficulty walking, running, rising from the floor or climbing the stairs, or may appear clumsy and fall often.
These may be early indications of muscular dystrophy. A child with MD may learn to walk later than other children do and may exhibit signs of muscle weakness between the ages of 2 and 6.
By school age, a child with MD may walk unsteadily and on the toes or balls of the feet. Duchenne's MD usually results in children losing the ability to walk by age 12.
See your doctor if you're concerned about your child's:
Motor abilities Clumsiness Muscle strength Muscle development
Once muscular dystrophy is diagnosed, medications and physical therapy can help slow its progression.
Because muscular dystrophies are inherited disorders, genetic counseling may be helpful if you're considering having children and to assess the risk of the disease in other family members.
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.
Tests and diagnosis
A careful review of your family's history of muscle disease can help your doctor reach a diagnosis. In addition to a medical history review and physical examination, your doctor may rely on the following in diagnosing muscular dystrophy:
Blood tests. Damaged muscles release enzymes such as creatine kinase (CK) into your blood. High blood levels of CK suggest a muscle disease such as muscular dystrophy.
Electromyography. A thin-needle electrode is inserted through your skin into the muscle to be tested. Electrical activity is measured as you relax and as you gently tighten the muscle. Changes in the pattern of electrical activity can confirm a muscle disease. The distribution of the disease can be determined by testing different muscles.
Ultrasonography. High-frequency sound waves are used to produce precise images of tissues and structures within your body. An ultrasound is a noninvasive way of detecting certain muscle abnormalities, even in the early stages of the disease.
Muscle biopsy. A small piece of muscle is taken for laboratory analysis. The analysis distinguishes muscular dystrophies from other muscle diseases. Special tests can identify dystrophin and other markers associated with specific forms of muscular dystrophy.
Genetic testing. Blood samples are examined for mutations in some of the genes that cause different types of muscular dystrophy. For Duchenne's and Becker's muscular dystrophies, standard tests examine just the portions of the dystrophin gene responsible for most cases of these types of MD. These tests identify deletions or duplications on the dystrophin gene in about two-thirds of people with Duchenne's and Becker's MDs.
The genetic defects responsible for Duchenne's and Becker's muscular dystrophies are harder to identify in other cases of those affected, but new tests that examine the entire dystrophin gene are making it possible to pinpoint tiny, less common mutations.
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, 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.
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.
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.
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.
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.
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.
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.
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.
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.
In early research, scientists were able to rid mice of muscle stiffness, weakness
By Amanda Gardner
THURSDAY, Nov. 15 (HealthDay News) -- When injected into mice, a novel compound eliminated the severe muscle stiffness and weakness that is a disabling symptom of one form of muscular dystrophy.
But the research, though promising, is still in its infancy, the investigators and other experts stressed.
"It's an important step forward that should be encouraging for people with the condition and their families and it shows that doctors and scientists are really now beginning to fix their attention on fixing this disease, rather than trying to understand what goes wrong," said study senior author Dr. Charles Thornton, a professor of neurology at the University of Rochester School of Medicine and Dentistry.
Thornton cautioned that he would not use the term "breakthrough" to describe the results, however.
"It's an important first step and these results are encouraging that effective therapies for myotonic [muscle-stiffening] dystrophy can be developed that can actually ameliorate some of the clinical symptoms," added Dr. Valerie Cwik, medical director and vice president of research at the Muscular Dystrophy Association (MDA). "But this is a study in mice, and we know from lots of other disorders and studies in mice that what works in mice doesn't always translate into effective therapy in humans."
According to the MDA, myotonic dystrophy is one of nine forms of muscular dystrophy, a group of genetic, degenerative and potentially disabling diseases which primarily affect voluntary muscles.
Myotonic dystrophy type 1 is the most common form of muscular dystrophy affecting adults. It is caused when a section of DNA is repeated on either chromosome 19 or chromosome 3.
"Myotonic dystrophy affects multiple systems in the body, so it causes central nervous system problems with altered cognition in some people, sleep disturbances, cataracts, droopy eyelids, not only myotonia," Cwik explained. Myotonia involves a "difficulty relaxing muscles but also muscle weakness, which is actually more disabling for many people," she said. It also involves "intestinal problems and, importantly, it can affect the heart, with potentially life-threatening arrhythmias," Cwik explained. "It's a multi-system disorder."
"Presently there is no cure. There are some treatments that help manage symptoms. They're not highly effective," Thornton added. "The disease has been known for 100 years but, until about six years ago, hardly anything was understood about what causes muscle problems. Now there are detailed theories about what's going wrong. This was an attempt to test one of those to see if symptoms could be fixed."
Five years ago, Thornton's team showed that a genetic flaw leads to the overproduction of a certain type of messenger RNA (mRNA) in cells, which affects muscle control and other cellular functions.
The current study, published online Nov. 15 in the Journal of Clinical Investigation, focuses on myotonia.
The researchers postulated that myotonia was caused by a problem with the pathway that electrical charges use to move in and out of muscle cells.
When researchers injected a synthetic molecule directly into the muscles of mice with myotonic dystrophy and then corrected the electrical control problem, the symptoms were eliminated.
"When a particular chemical imbalance in the muscle tissue was restored, it eliminated stiffness," Thornton said. "This would be a partial solution to the person's symptoms with myotonic dystrophy, but it's also proof of principle that once we identify the cause that it can be corrected."
Considerably more work is needed, however.
For one thing, scientists need to find a way to inject the compound into a person's bloodstream so a systemic effect would take place. Injecting into muscles spurs only a local effect. "That's one obstacle that must be overcome in getting wide distribution," Thornton said.
Safety issues also have to be considered before human trials begin, Cwik added.
"They are only looking at one symptom of myotonic dystrophy," she noted. "Would this therapy or kind of therapy, which can reverse or eliminate myotonia, have any effect on some of the other potentially more disabling symptoms? While it's encouraging, there are a lot of cautions and caveats."
There's more on myotonic dystrophy at the Muscular Dystrophy Association.
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Self Care for Muscular Dystrophy
For family members of people with muscular dystrophy, coping with the illness involves a major commitment of physical, emotional and financial effort. The disease presents challenges in the classroom, in the home and in all aspects of life.
In dealing with a disease such as muscular dystrophy, support groups can be a valuable part of a wider network of social support that includes health care professionals, family, friends and a place of religious worship.
Support groups bring together people, family and friends who are coping with the same kind of physical or mental health challenge. Support groups provide a setting in which people can share their common problems and provide ongoing support to one another.
Ask your doctor about self-help groups that may exist in your community. Your local health department, public library, telephone book and the Internet also may be good sources to locate a support group in your area.
What are Muscle disorders?
Movement disorders are a group of diseases and syndromes affecting the ability to produce and control movement. Though it seems simple and effortless, normal movement in fact requires an astonishingly complex system of control.
Disruption of any portion of this system can cause a person to produce movements that are too weak, too forceful, too uncoordinated, or too poorly controlled for the task at hand. Unwanted movements may occur at rest.
Intentional movement may become impossible. Such conditions are called movement disorders.
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