Muscular Dystrophy

 

Reprinted with Permission KidsHealth

 

The term muscular dystrophy refers to a group of degenerative muscle diseases characterized by gradual weakening and deterioration of skeletal muscles and sometimes the heart and respiratory muscles. Children with the disease are born with an abnormal genetic trait that causes their muscles to develop improperly.

 

The most common types of muscular dystrophy result in dramatic physical weakness, so children lose the ability to do things like walk, sit upright, breathe easily, and move their arms and hands. The increasing weakness often leads to other serious complications and, for many, a shortened life span. Other forms can result in relatively minor physical disabilities or develop late in life, allowing affected people to have fairly normal life spans and activity levels. Intelligence does not deteriorate along with the muscles.

 

In most cases, the genetic abnormality for muscular dystrophy is inherited, so the condition tends to run in families. Some types of muscular dystrophy, including the most severe type, Duchenne, are X-linked, which means that the abnormality is carried on the X chromosome that the mother contributes. A girl receives two X chromosomes, one from each parent, whereas a boy receives a Y chromosome from the father and an X from the mother. As a result, it is almost always boys who develop symptoms; girls inherit a normal X chromosome that may cancel out the abnormal one. These girls are called carriers of the muscular dystrophy gene, but have no muscle weakness themselves. Girls who carry the abnormal gene have a 50% chance of passing the condition to their sons.

The different types of muscular dystrophy affect different sets of muscles and result in different degrees of muscle weakness.

 

What Are the First Symptoms of Muscular Dystrophy?


Dr. Harold Marks, a neurologist specializing in muscular dystrophy, says that many parents first learn of a potential problem from a teacher who notices that their child just "isn't as active as other children." Many children with muscular dystrophy have had a normal pattern of development during their first few years, so at first, parents may not be overly concerned.

 

But in time other typical symptoms begin to appear. Parents may notice that their child stumbles more frequently, waddles, has difficulty going up stairs, and toe walks (walks on the toes without the heels hitting the floor). Toddlers may develop a swayed back to compensate for weakening hip-area muscles. Children may struggle to get up from a sitting position or have a hard time pushing things, like a wagon or a tricycle. Many children also develop enlarged calf muscles, a condition called calf pseudohypertrophy, as muscle tissue is destroyed and replaced by non-muscle tissue.

 

Symptoms can first appear during early childhood or late in adult life, depending on the type of muscular dystrophy. For example, the symptoms of Becker muscular dystrophy may start during the school-age years, are less severe, and allow children to live well into adulthood. In contrast, Duchenne muscular dystrophy begins during early childhood and causes fairly rapid weakness.

 

How Is Muscular Dystrophy Diagnosed?


When a doctor first suspects a child has muscular dystrophy, he or she will perform some preliminary tests and take a detailed family history.

 

"In addition to a clinical history and a physical exam, we perform a test that measures blood levels of serum creatine kinase, a muscle enzyme that's released into the bloodstream when muscle fibers are deteriorating in the body; elevated levels indicate that something is causing muscle damage," Dr. Marks says. If a child is found to have a high level of this enzyme, the next test may be a DNA test or a muscle biopsy. The DNA test is used to check for gene abnormalities, whereas the muscle biopsy is used to examine a muscle tissue sample for patterns of muscle deterioration and abnormal levels of dystrophin, a building block of muscle. These tests reveal the type of muscular dystrophy the child has.

 

Types of Muscular Dystrophy


According to Dr. Marks, most types of muscular dystrophy are the result of "different abnormalities in the genes, or blueprints, that produce muscle membrane proteins." Typically, the genetic abnormality is inherited from one or both parents, but in some cases, it develops spontaneously. The genetic abnormality results in the development of muscle membranes with missing or malformed parts, causing muscle deterioration and weakness. The most common types of muscular dystrophy follow.

 

Duchenne muscular dystrophy occurs when muscle fibers develop with abnormal dystrophin. Duchenne is the most common and most severe form of the disease, affecting about one out of every 3,300 boys. Children usually begin to show symptoms between ages 2 and 5, with rapid muscle weakness first affecting the pelvic muscles. Most children lose the ability to walk by age 12 and must use a wheelchair. Over time, children develop progressive muscle weakness in their shoulders, back, arms, legs, and finally their respiratory muscles, resulting in a shortened life span, typically about 20 years. Although most children have average intelligence, learning disabilities - particularly those involving verbal learning and reading comprehension - are more common in boys with Duchenne muscular dystrophy than in other children.

 

Becker muscular dystrophy is similar to Duchenne, but it progresses more slowly. Symptoms typically begin during adolescence but can begin as early as age 5 or as late as age 25. Muscle weakness first occurs in the pelvic muscles, so most children eventually lose the ability to walk. As the disease progresses, they also lose strength in their shoulders and back. Because Becker progresses so slowly, many children with Becker have a normal life span.

 

Myotonic dystrophy is the most common adult form of muscular dystrophy, although 50% of cases are diagnosed in people younger than 20. The main symptoms include facial weakness, myotonia (a very slow relaxation of the muscles after contraction), and pronounced weakness in the hand muscles that results in the inability to release the hand from a grip. 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 his or her child. A less common congenital (present at birth) form affects only a small number of infants born to mothers with myotonic dystrophy but carries a worse prognosis.

 

Limb-girdle muscular dystrophy symptoms begin between ages 5 and 30, first affecting either the pelvic muscles or the shoulder and back muscles. As the disease progresses, both areas are affected eventually. The severity of muscle weakness resulting from limb-girdle muscular dystrophy varies from person to person, as does the rate at which muscle weakness progresses. Some people develop only mild conditions, but many develop severe disabilities by middle age.

 

Facioscapulohumeral muscular dystrophy can begin at any age but typically first appears during adolescence. Because this form of muscular dystrophy tends to progress slowly, people who are affected usually have a normal life span. Muscle weakness first develops in the face, making it difficult for children to close their eyes, whistle, or puff out their cheeks. The shoulder and back muscles gradually become weak, and those affected find it hard to lift objects or raise their hands over their head. Over time, the legs and pelvic muscles also lose strength. People can develop only minor physical symptoms (for example, sleeping with open eyes) or more profound disabilities.

In rare cases, infants can develop symptoms during their first and second year, resulting in expressionless faces and serious muscle weakness during early childhood.

 

Congenital muscular dystrophy is a group of disorders. Those affected share two unique characteristics: they have muscle weakness at birth, 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 muscular dystrophy affect the brain, causing tissue abnormalities and seizures. These children do less well and experience continued deterioration.

 

Other types of muscular dystrophy, which are rare, include distal, ocular, oculopharyngeal, and Emery-Dreifuss.

 

Caring for a Child With Muscular Dystrophy


"Muscular dystrophy is a treatable but not curable disease, but we're working on a cure," Dr. Marks says. "Kids are living longer and having a better quality of life because we have new treatments." These treatments 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 together with the family to give a child with muscular dystrophy the best possible care: a neurologist, orthopedist, pulmonologist, physical and occupational therapist, nurse practitioner, and a social worker.

 

Muscular dystrophy is often degenerative, so kids may pass through different stages as the disease progresses. Doctors use different treatments to care for kids in each stage. A combination of physical therapy, joint bracing, and a medication known as prednisone may be used to treat children in the early stage of the condition, whereas assistive technology may be the focus of later stages.

 

Physical Therapy and Bracing


Physical therapy helps maintain muscle tone and reduce the severity of joint contractures. A physical therapist uses exercises to help keep muscles strong and joints flexible.

 

A physical therapist also uses bracing techniques, fitting special supports to a child's joints and limbs. Bracing helps prevent contractures and enables kids to use weakened muscles and joints more effectively. By providing extra support in just the right places, bracing allows kids to do more things independently for a longer period of time - including walking.

 

Prednisone


Prednisone, a steroid that has been shown to slow the rate of muscle deterioration in children with Duchenne muscular dystrophy, may also be prescribed. When the rate of muscle deterioration is slowed, kids with muscular dystrophy can often walk longer and live more active lives. "I have kids taking prednisone whose rate of muscle deterioration has slowed dramatically," Dr. Marks notes. "In some cases, kids with Duchenne dystrophy are still walking in late junior high school, when you would expect them to be in a wheelchair."

 

There is some debate over the best time to begin treating children with prednisone, but most doctors prescribe it when children are 5 or 6 or when they show a significant decline in strength. A common side effect of prednisone, though, is that it causes weight gain, and extra weight may put even greater strain on already weak muscles. Prednisone can also cause a loss of bone density and potentially lead to fractures.

 

Sometimes prednisone doesn't slow the rate of muscle deterioration and researchers aren't sure why. For this reason, doctors closely monitors their patients' weight and blood pressure, trying to improve muscle strength without causing excessive weight gain.

 

Spinal Fusion


Most kids with Duchenne and Becker dystrophy develop severe scoliosis - an S- or C-shaped curvature of the spine that develops when the back muscles are too weak to hold the spine erect. Some may undergo spinal fusion, a surgery that involves placing a pair of metal rods down the length of the spine and fusing the vertebrae together. The procedure enables children to 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. The goals of spinal fusion are to prevent pain, ensure proper wheelchair seating, improve a child's body image, and enable a child to use the most comfortable, least-invasive respiratory aids (a severe curvature can cause difficulty breathing).

 

Today, children who undergo spinal fusion no longer need to be in a body cast to heal - they may be out of the hospital in about a week.

 

Respiratory Care


Many children with muscular dystrophy also develop weakened heart and respiratory muscles. Dr. David Hammond, a pediatric neurologist, notes that because children can't cough out phlegm due to weakened respiratory muscles, they sometimes develop respiratory infections that can quickly become serious. Good general health care and regular vaccinations are especially important for children with muscular dystrophy to prevent these infections.

 

Assistive Technology


"Independence and mobility are the most important things to help children with. And for kids with muscular dystrophy, there's always a way for them to have some independence, to get around and go to school and other activities," says Anjali Weber, a specialist in assistive technology. Many children with Duchenne muscular dystrophy may use a manual wheelchair when walking is no longer efficient. Some children may go directly to a motorized wheelchair to conserve energy expenditure. Technology experts can custom design controls for wheelchairs so kids can maneuver them with a joystick, infrared technology, or highly sensitive switches as the weakness increases. "No matter what," Weber says, "we'll find a way for a child to get around."

Homes can also be equipped with environmental controls that can be activated by switch, infrared, or voice to accommodate kids with limited physical mobility. "There are all sorts of controls for lights, doors, and appliances such as the TV and VCR. They let kids change channels, open doors, turn lights on and off, and play videos as they want to, making them much more independent," Weber explains.

 

One very exciting area of assistive technology is robotics, Weber says. "It's expensive and not mainstream right now, but there's a lot of research going on around the world to help kids with muscular dystrophy manipulate things in their environment."

 

She adds that many kids with Duchenne have the potential to go on to college by planning ahead to have the right assistive devices. "With the right computer, wheelchair, and other technology, and the will to do it, many kids can take college classes or go to work," Weber says. There are voice-activated word processors for writing and dictation, mini keyboards requiring less hand and arm movement to type, spelling and grammar checks, and even word processors that give the best word choices and speed up the process of writing. "We can even link a joystick or fingertip controls to a computer to use as a mouse that can select letters on the keyboard," she adds.

 

Parents can contact the local Muscular Dystrophy Association to find out if the association offers financial help to pay for assistive technology. "Many of the mobility technologies are paid for by insurance companies, but often computers and environmental controls aren't," Weber says. Many school districts also have discretionary money to spend on children with special needs if the technology enables them to reach their educational goals.

 

The Search for a Cure


Researchers are quickly discovering new information about muscular dystrophy, which helps doctors and other researchers better understand its causes, patterns of development, and possible treatments. Both Dr. Marks and Dr. Hammond agree that the most promising cure involves gene therapy. In the case of Duchenne and Becker dystrophy, researchers are working on ways to introduce normal dystrophin into a genetically engineered virus that can then bind to afflicted muscle cells. Once bound to muscle cells, researchers hope the virus can transfer its normal dystrophin gene to the weakened muscles, enabling them to reproduce normal dystrophin and become stronger.