Types of Muscular Dystrophy

There are many types of muscular dystrophy; of these Duchenne is the most common and most severe.

Duchenne This type of MD occurs when muscle fibers develop with abnormal dystrophin. Duchenne affects about one out of every 3,300 boys, who usually begin to show symptoms between ages two and five, with rapid muscle weakness first affecting the pelvic muscles. Most children lose the ability to walk by age 12 and must use a wheelchair, eventually developing muscle weakness in shoulders, back, arms, and legs. Even tually the muscles involved in breathing weaken, which can be fatal. Typically, children with Duchenne MD live only to about age 20 years. Although most children have average intelligence, learning disabilities (especially those involving verbal learning and reading comprehension) are more common in boys with Duchenne than in other children.

Becker This type of MD is similar to Duchenne, but it progresses more slowly. Symptoms typically begin during adolescence, although they can first appear as early as age five or as late as age 25. Muscle weakness first occurs in the pelvic muscles, affecting the ability to walk. As the disease progresses, strength in the shoulders and back is also affected. Because Becker progresses so slowly, many children with Becker have a normal life span.

Myotonic This is the most common adult form of MD, although half of all cases are still diagnosed in patients younger than 20. Primary symptoms involve facial weakness, a very slow relaxation of muscles after contraction, and weak hand muscles. The disease may be mild or severe, but because the defective gene is dominant, even someone with mild symptoms can transmit a more serious case of it to offspring. A less common congenital form affects only a small number of infants born to mothers with myotonic dystrophy, but it has a worse prognosis.

Limb-girdle This type of MD begins between ages five and 30, first affecting either the pelvic muscles or the shoulder and back muscles; eventually both areas are affected. The severity of muscle weakness differs from person to person, as does the rate at which muscle weakness progresses. Some people develop only mild conditions, but many others develop severe disabilities by middle age.

Facioscapulohumeral This type of MD can begin at any age, although it typically first appears during adolescence. Because this form of muscular dystrophy tends to progress slowly, teens who are affected usually have a normal life span. Muscle weakness first develops in the face, making it hard for children to close their eyes, whistle, or puff out their cheeks. The shoulder and back muscles gradually weaken, until it is hard for patients to lift objects or raise their hands over their head. Over time, the legs and pelvic muscles also lose strength. Some people develop minor physical symptoms (such as not being able to close the eyes during sleep), while others have profound disabilities. Rarely, infants develop symptoms during the first year or two of life, resulting in expressionless faces and serious muscle weakness during early childhood.

Congenital This type of MD is actually a group of disorders with two unique characteristics: At birth, babies have weak muscles, often causing joint contractures and deformities, and muscle biopsies show nonspecific abnormalities. Joint contractures occur when muscles attached to a joint have unequal strength; the stronger muscle pulls and bends the joint into a locked and nonfunctional position. A combination of the facial, arm and leg, pelvic, respiratory, and shoulder muscles can be weak at birth, but this muscle weakness rarely gets worse.

Some types of congenital MD affect the brain, triggering seizures and gradual but constant deterioration.

Other There are several other types of rare muscular dystrophy, including distal, ocular, ocu-lopharyngeal, and Emery-Dreifuss.

Treatment

Muscular dystrophy is a treatable but not curable disease, although affected children today live longer and have a better quality of life due to new treatments that improve muscle and joint function, slow muscle deterioration, and keep kids comfortable, active, and independent for a longer period of time.

A team of medical specialists will work with the family of an affected child, including a neurologist, orthopedist, pulmonologist, physical and occupational therapist, nurse practitioner, and a social worker.

Different treatments are used to care for children at different stages of the disease. A combination of physical therapy, joint bracing, and prednisone treat children in the early stage, whereas assistive technology may be used in later stages.

Physical therapy and braces The primary treatment for early MD is passive muscle stretching to maintain muscle tone and joint movement to reduce contractures. Leg braces also can help prevent contractures and enable children to stand and walk using weakened muscles and joints more effectively. By providing extra support in just the right places, bracing lets children do more things independently for a longer period of time.

Prednisone This steroid medication has been shown to slow the rate of muscle deterioration in children with Duchenne muscular dystrophy, which allows children to walk longer and live more active lives. In some cases, children with Duchenne are still walking in late junior high school, when in the past they would have been in a wheelchair.

Experts do not agree about the best time to begin treating children with prednisone, but most doctors prescribe it when children are five or six or when they show a significant decline in strength. Unfortunately, prednisone commonly causes weight gain, which may strain already weak muscles. It also can cause a loss of bone density that could lead to fractures.

For unknown reasons, sometimes prednisone does not slow the rate of muscle deterioration. For this reason, doctors closely monitor a child's weight and blood pressure, trying to improve muscle strength without causing excessive weight gain.

Surgery If joints become contracted, orthopedic surgery can help improve function.

Spinal fusion Most children with Duchenne and Becker dystrophy develop a severe curvature of the spine because the back muscles are too weak to hold the spine straight. Some children may undergo spinal fusion to place a pair of metal rods down the length of the spine so that they can sit upright in a chair and be more comfortable. Usually, a child with muscular dystrophy is a candidate for spinal fusion when there is a 25-degree spinal curvature.

Respiratory care Many children with muscular dystrophy develop weakened heart and respiratory muscles and sometimes develop serious respiratory infections because they cannot cough out mucus easily. Good general health care and regular vaccinations are especially important for children with muscular dystrophy to prevent these infections.

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