(Also Called 'Becker Muscular Dystrophy', 'Congenital Muscular Dystrophy', 'Distal Muscular Dystrophy', 'Duchenne Muscular Dystrophy', 'Emery-dreifuss Muscular Dystrophy', 'Facioscapular Muscular Dystrophy', 'Limb-girdle Muscular Dystrophy', 'MD (Muscular Dystrophy)', 'Myotonic Muscular Dystrophy')
Muscular dystrophy (MD) refers to a group of genetic diseases characterized by progressive damage and weakness of facial, limb, breathing, and heart muscles. It is due to the lack of a key protein that is needed to maintain the integrity and proper function of the muscle. As the muscle tissue is damaged, the muscle bulk is reduced. Sometimes the muscle tissue can be replaced with fat and excessive scar tissue to make muscle appears larger than normal.
MD is categorized as listed below based on the clinical features, including inheritance pattern, muscles affected, and muscle biopsy features:
- Myotonic dystrophy
More than 30 genes have been identified to cause different types of muscular dystrophies. Many muscular dystrophies are now diagnosed through gene tests.
MD can affect people of all ages. Although some forms first become apparent in infancy or childhood, others may not appear until middle age or later. Duchenne muscular dystrophy is the most common form affecting children, while myotonic MD is the most common form affecting adults.
There are three primary types of inheritance in which the faulty gene that causes MD can be passed along to offspring:
- X-linked recessive: Genes that are X-linked recessive are carried by the female on one of the X chromosomes that determine the sex of the child. As such, only boys will inherit conditions determined by these genes. Their mothers, known as carriers, will usually not show signs of the disease. A son of a carrier of MD has about a 50 percent chance of developing the disease, while a daughter of a carrier has a 50 percent chance of being a carrier. If a boy is unaffected, he cannot pass on MD; however, daughters from a man with an X-linked dystrophy will all be carriers. Duchenne/Becker and Emery-Dreifuss are X-linked recessive.
- Autosomal recessive: For this type of inheritance, both parents must carry and pass on the faulty gene. Neither parent shows any symptoms, but each of their offspring, regardless of gender, will have a 25 percent chance of developing the disease. Limb-girdle type 2 MD and distal myopathy are autosomal recessive.
- Autosomal dominant: In the case of autosomal dominant inheritance, an affected person will have MD even though only one faulty gene has been passed along. This faulty gene can come from either parent, and it can affect either sex. Each child of an affected parent will have a 50 percent chance of developing MD. For this type of inheritance, the severity of MD can vary greatly. It can be so mild that it is not recognized, but it can also be severe. Myotonic dystrophy, facioscapulohumeral dystrophy (FSHD), and oculopharyngeal muscular dystrophy (OPMD) are autosomal dominant.
After carefully evaluating a patient’s medical history, the doctor will perform a thorough physical exam to rule out other causes. If MD is suspected, there are a variety of laboratory tests that can be used to solidify a diagnosis. These tests may include:
- Blood tests: When blood tests are performed to test for MD, the doctors are looking for an enzyme called creatine kinase (CK). This enzyme rises in the blood due to muscle damage or deterioration and may reveal some forms of MD before any physical symptoms appear.
- Muscle biopsy: During a muscle biopsy, a small piece of muscle tissue is removed and then examined under a microscope. If MD is present, changes in the structure of muscle cells and other characteristics of the different forms of MD can be detected. The sample can also be stained to detect the presence or absence of particular proteins.
- Electromyogram (EMG): An EMG is a test that measures the muscle’s response to stimulation of its nerve supply (nerve conduction study) and the electrical activity in the muscle (needle electrode examination). This test will confirm that the muscle weakness is due to a muscle disease, not a nerve disease.
- Genetic tests: Many muscular dystrophies can be definitively diagnosed by testing for the mutated genes. The gene tests can spare muscle biopsies in these MD, including Duchenne, Becker, myotonic dystrophy, FSHD, OPMD, Distal, several forms of Limb-girdle, and Emery-Dreifuss dystrophies.
There is no cure for muscular dystrophy, although some drugs still in the trial stage have shown promise in slowing or delaying the progression of the disease. The only FDA-approved drug for Duchenne is a steroid, which may prolong ambulation by 2 years. For the time being, treatment is aimed at preventing complications due to the effects of weakness, decreased mobility, contractures, scoliosis, heart defects, and respiratory weakness.
Physical therapy: Physical therapy, especially regular stretching, is important in helping to maintain the range of motion for affected muscles and to prevent or delay contractures. Strengthening other muscles to compensate for weakness in affected muscles may be of benefit also, especially in earlier stages of milder MD. Regular exercise is important in maintaining good overall health, but strenuous exercise may damage muscles further. For patients whose leg muscles are affected, braces may help lengthen the period of time that they can walk independently.
Surgery: If a patient’s contractures have become more pronounced, surgery may be used to relieve the tension by cutting the tendon of the affected muscle, then bracing it in a normal resting position while it regrows.
Other surgeries are used to compensate for shoulder weakness in facioscapulohumeral MD, and to keep the breathing airway open for people with distal MD who sometimes experience sleep apnea. Surgery for scoliosis is often needed for patients with Duchenne MD.
Occupational therapy: Occupational therapy involves employing methods and tools to compensate for a patient’s loss of strength and mobility. This may include modifications at home, dressing aids, wheelchair accessories, and communication aids.
Nutrition: Nutrition has not been shown to treat any conditions of MD, but it is essential to maintaining good health.
Cardiac care: Arrhythmias are often a symptom with Emery-Dreifuss and Becker MD and may need to be treated with special drugs. Pacemakers may also be needed in some cases, and heart transplants are becoming more common for men with Becker MD.
Respiratory care: When the muscles of the diaphragm and other respiratory muscles become too weak to function on their own, a patient may require a ventilator to continue breathing deeply enough. Air may also be administered through a tube or mouthpiece. It is therefore very important to maintain healthy lungs to reduce the risk of respiratory complications.
Like many other disorders, understanding and education about muscular dystrophy is the most important tool with which to manage and prevent complications. The following organizations can provide more information about muscular dystrophy:
The Muscular Dystrophy Association
3300 E. Sunrise Drive
Tucson, AZ 85718
Muscular Dystrophy Family Foundation
3951 N. Meridian Street, Suite 100
Indianapolis, Indiana 46208
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This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 3/25/2008…#14128