Alternative Names pseudohypertrophic muscular dystrophy
Definition Duchenne muscular dystrophy is an inherited disorder of the muscles. It causes the muscles to degenerate and lose their function.
What is going on in the body? Duchenne muscular dystrophy occurs in about 1 in 3500 males. There is a family history in 70% of affected people. The disorder is present at birth, but usually doesn't become apparent until 3 to 5 years of age. Affected children may fall frequently and have difficulty keeping up with playmates. Running, jumping, and hopping are abnormal. The calf muscles are unusually large.
By 5 to 6 years of age, the enlarged muscle is replaced by fat and connective tissue. Muscle weakness is obvious. Affected children use their hands to rise from a sitting position. This is because the muscles nearest the hips weaken before the lower leg muscles. Legs are more severely affected than arms. Tendons around the heels tighten, which causes affected children to walk on their toes.
Between 8 and 10 years of age, tendons tighten around the hips, knees, elbows, and wrists. Braces may be needed.
By 12 years of age, the child is usually using a wheelchair. Curvature of the spine begins. With time, the curvature and weakening chest muscles impair lung function.
By 16 to 18 years of age, breathing is so weak that lung infections or aspiration of food become problems. Such problems are the common causes of death.
The heart muscle becomes enlarged in almost all affected people. Heart problems are not common causes of death, though. Intellectual impairment is common and does not seem to get worse over time. The reason for the intellectual impairment is not known.
What are the signs and symptoms of the disease? The symptoms include:
large calf muscles
walking on the toes
using the hands to rise from a sitting position, called Gower's sign
progressive muscle deterioration, starting with the muscles nearest the hips
curvature of the spine
enlargement of the heart muscle
What are the causes and risks of the disease? The risk of developing Duchenne muscular dystrophy depends on a variety of genetic factors.
What can be done to prevent the disease? Since Duchenne muscular dystrophy is an inherited disorder, genetic counselling may helpful to couples with a family history of the disease.
How is the disease diagnosed? High levels of creatinine phosphokinase, or CPK, in the blood can confirm the diagnosis. These levels are 20 to 100 times the normal amounts. Electromyography, or EMG, shows the typical features of a muscle dystrophy. Muscle biopsy shows degenerating and regenerating muscle fibres, with connective tissue and fat replacing lost muscle tissue. DNA testing may also be done.
What are the long-term effects of the disease? Duchenne muscular dystrophy causes progressive deterioration of the muscles, and loss of function. The muscle deterioration leads to the use of braces and eventually a wheelchair. Impaired lung function leads to serious lung infections, aspiration, and death.
What are the risks to others? Duchenne muscular dystrophy is not contagious. It is an X-linked recessive disorder. This means that an unaffected woman who carries the gene can pass it to her sons.
What are the treatments for the disease? The major goal of early treatment is to keep the ability to walk as long as possible. Stretching exercises and using braces at night help avoid the tightening of tendons.
Surgery can be used to release tight tendons. Walking and body movement should be resumed immediately after surgery if possible. Inactivity makes the disease worse and can lead to rapid deterioration of lung function.
Prednisone has been shown to slow the progression of the disease for up to three years.
How is the disease monitored? Any new or worsening symptoms should be reported to the doctor.
Author: Reviewer: HealthAnswers Australia Medical Review Panel Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia Last Updated: 1/10/2001 Contributors Potential conflict of interest information for reviewers available on request
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