Alternative names pseudohypertrophic muscular dystrophy; muscular dystrophy - Duchenne's
Definition An inherited disorder characterized by rapidly progressive muscle weakness of the legs and pelvis; later affecting the whole body. Causes, incidence, and risk factors Duchenne's muscular dystrophy is a rapidly progressive form of muscular dystrophy. A slowly progressive muscular dystrophy that is very similar to Duchenne's also exists (Becker's muscular dystrophy). Duchenne's muscular dystrophy is an inherited disorder.
Symptoms appear before age 6 and may appear as early as infancy. There is progressive muscle weakness of the legs and pelvis, which is associated with a loss of muscle mass (wasting). Muscle weakness also occurs in the arms, neck, and other areas, but not as severely as in the lower half of the body. Calf muscles initially enlarge; the enlarged muscle tissue is eventually replaced by fat and connective tissue (pseudohypertrophy). Muscle contractures occur in the legs and heels, causing inability to use the muscles because of shortening of muscle fibers and fibrosis of connective tissue.
By age 10, braces may be required for walking, and by age 12, most patients are confined to a wheelchair. Bones develop abnormally, causing skeletal deformities of the chest and other areas. Muscular weakness and skeletal deformities contribute to frequent breathing disorders. Cardiomyopathy occurs in almost all cases. Intellectual impairment is common but is not inevitable and does not worsen as the disorder progresses. The cause of this impairment is related to an abnormal gene for dystrophin protein (a specific type of protein in the body).
Duchenne's muscular dystrophy occurs in approximately 2 out of 10,000 people. Symptoms usually appear in males 1 to 6 years old. Females are carriers of the gene for this disorder but rarely develop symptoms. Because this is an inherited disorder, risks include a family history of Duchenne's muscular dystrophy. Prevention Genetic counseling is advised if there is a family history of the disorder. Duchenne's muscular dystrophy can be detected with about 95% accuracy by genetic studies performed during pregnancy. Symptoms
muscle weakness
rapidly progressive
frequent falls
difficulty with muscle skills (running, hopping, jumping)
progressive difficulty walking
ability to walk may be lost by age 12
fatigue
intellectual retardation (possible)
skeletal deformities
chest and back (scoliosis)
muscle deformities
contractures of heels, legs
pseudohypertrophy of calf muscles
Signs and Tests Muscle wasting (atrophy) begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy is commonly present but signs of congestive heart failure or arrhythmias (irregular heartbeats) are rare. Respiratory disorders are common during the later stages, including pneumonia and aspiration of food or fluid into the lungs.
A serum CPK is highly elevated.
An EMG (electromyography) shows that weakness is caused by destruction of muscle tissue rather than nerve damage.
A muscle biopsy confirms the diagnosis.
Treatment There is no known cure for Duchenne's muscular dystrophy. Treatment is aimed at control of symptoms to maximize the quality of life.
Activity is encouraged. Inactivity (such as bedrest) can worsen the muscle disease. Physical therapy may be helpful to maintain muscle strength and function. Orthopedic appliances such as braces and wheelchairs may improve mobility and the ability for self-care. Support Groups The stress of illness can often be helped by joining a support group where members share common experiences and problems. See muscular dystrophy - support group. Expectations (prognosis) Duchenne's muscular dystrophy results in rapidly progressive disability. Death usually occurs by age 15, typically from respiratory (lung) disorders.
