Duchenne Muscular Dystrophy (DMD)

What is Duchenne muscular dystrophy?

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration and weakness. It is one of nine types of muscular dystrophy.

DMD is caused by an absence of dystrophin, a protein that helps keep muscle cells intact. Symptom onset is in early childhood, usually between ages 3 and 5. The disease primarily affects boys, but in rare cases it can affect girls.

Signs and Symptoms

Boys with DMD often have enlarged calf muscles.

Children with Duchenne muscular dystrophy (DMD) are often late walkers.

In toddlers, parents may notice enlarged calf muscles (see image at right). This enlargement is known as pseudohypertrophy, or "false enlargement," because the muscle tissue is abnormal and may contain scar tissue.

A preschooler with DMD may seem clumsy and fall often. Parents also may note that children have trouble climbing stairs, getting up from the floor or running.

By school age, children may walk on their toes or the balls of their feet with a slightly waddling gait, and fall frequently. To try to keep their balance, they may stick out their bellies and pull back their shoulders. Children also have difficulty raising their arms.

Many children with DMD begin using a wheelchair sometime between ages 7 and 12. Transition to a wheelchair usually is a gradual process; at first, the chair may be required only to conserve the child's energy when covering long distances. (Children often experience renewed independence once they fully transition to a power wheelchair.)

In the teen years, activities involving the arms, legs or trunk may require assistance or mechanical support.Pain and sensation

Pain and sensation

The muscle deterioration in Duchenne MD isn’t usually painful in itself. Some people report muscle cramps at times; these usually can be treated with over-the-counter pain relievers.

Because muscular dystrophy doesn’t affect nerves directly, touch and other senses are normal, as is control over the smooth, or involuntary, muscles of the bladder and bowel, and sexual functions.

The heart

Lack of dystrophin can weaken the muscle layer in the heart (myocardium), resulting in a condition calledcardiomyopathy. Over time, sometimes as early as the teen years, the damage done by DMD to the heart can become life-threatening. The heart should be monitored closely, usually by a pediatric cardiologist. See Medical Management for more on cardiomyopathy in DMD.

Respiratory function

Beginning at about 10 years of age, the diaphragm and other muscles that operate the lungs may weaken, making the lungs less effective at moving air in and out. Although the child may not complain of shortness of breath, problems that indicate poor respiratory function include headaches, mental dullness, difficulty concentrating or staying awake, and nightmares.

Weakened respiratory muscles make it difficult to cough, leading to increased risk of serious respiratory infection. A simple cold can quickly progress to pneumonia. It's important to get flu shots, and when infections occur, to get prompt treatment. See Medical Management for more on respiratory care in DMD.

Learning

About a third of boys with DMD have some degree of learning disability, although few have serious mental retardation. Doctors believe that dystrophin abnormalities in the brain may have subtle effects on cognition and behavior. Learning problems in DMD occur in three general areas: attention focusing, verbal learning and memory, and emotional interaction.

Children suspected of having a learning disability can be evaluated by a developmental or pediatric neuropsychologist through the school system’s special education department or with a referral from the MDA clinic.

If a learning disability is diagnosed, educational and psychological interventions can begin right away. The specialist may prescribe exercises and techniques that can help improve these areas, and the school also can provide special help with learning. See Medical Management for more about learning disabilities in DMD.

Medical Management

Thanks to advances in many areas of medicine, such as cardiology and pulmonology, people with Duchenne muscular dystrophy in the 21st century are living longer than in previous decades, often well into adulthood. As of 2011, most therapies for DMD are supportive in nature, but research to develop truly disease-modifying therapies is under way.

The use of available treatments can help maintain comfort and function and prolong life. Talk with an MDA clinic physician for more information.

Anesthesia

People with DMD may have unexpected adverse reactions to certain types of anesthesia. It's important that the surgical team know about the patient's DMD so that complications can be avoided or quickly treated.

Braces, standing frames and wheelchairs

Braces, also called orthoses, support the ankle and foot, or may extend up over the knee. Ankle-foot orthoses (AFOs) are sometimes prescribed for night wear to keep the foot from pointing downward and keep the Achilles tendon stretched while the child is sleeping.

Standing for a few hours each day, even with minimal weight bearing, promotes better circulation, healthier bones and a straight spine. A standing walker or standing frame can assist people with DMD to stand. Some wheelchairs will raise the user into a standing position.

Sooner or later, a wheelchair is needed in DMD, typically by about age 12. Unless there's an injury, such as a broken leg, wheelchair use usually is gradual. Many at first use wheelchairs for long distances, such as at school or the mall, and continue to walk at home.

Although the child and parents may dread the wheelchair as a symbol of disability, most find that when they start to use one, they are actually more mobile, energetic and independent than when trying to walk.

Other mobility and positioning aids can help parents and caregivers. Among the simplest aid is a transfer board for helping the person move in and out of the wheelchair. Mechanical lifts, shower chairs and electronic beds also can be useful.

MDA's national equipment program may be able to help families obtain some needed equipment.

Also see:

• Putting Your Best Foot Forward

• Stand Up and Go with Mobile Standers and Standing Wheelchairs

Cardiac care

The American Academy of Pediatrics recommends that people with DMD have a complete cardiac evaluation by a specialist beginning in early childhood and again at least every other year until age 10. After that, the evaluations should be done every year or at the onset of symptoms of heart weakness, such as fluid retention or shortness of breath.

Female carriers of DMD are at higher-than-average risk of developing cardiomyopathy. The academy suggests that carriers should undergo a complete cardiac evaluation in late adolescence or early adulthood, or sooner if symptoms occur, and that they should be evaluated every five years starting at age 25 to 30.

There’s some preliminary evidence that treatment with angiotensin converting enzyme (ACE) inhibitors and beta blockers can slow the course of cardiac muscle deterioration in DMD if the medications are started as soon as abnormalities on an echocardiogram (ultrasound imaging of the heart) appear but before symptoms occur.

Also see:

• Doctors Talk Heart to Heart (pediatric cardiologists and other experts at an MDA-sponsored meeting exchanged information and planned studies regarding the heart in DMD and BMD)

• Revising Cardiac Care in Muscular Dystrophies

Contractures

The impact of DMD can be minimized significantly by keeping the body as flexible, upright and mobile as possible. There are several ways to do this.

As muscle deteriorates, a person with muscular dystrophy often develops fixations of the joints, known ascontractures. If not treated, these will become severe, causing discomfort and restricting mobility and flexibility. Contractures can affect the knees, hips, feet, elbows, wrists and fingers.

However, there are many ways to minimize and postpone contractures. Range-of-motion exercises, performed on a regular schedule, help delay contractures by keeping tendons from shortening prematurely. It’s important that a physical therapist show you how to do range-of-motion exercises correctly.

Braces on the lower legs also can help keep the limbs stretched and flexible, delaying the onset of contractures.

When contractures have advanced, surgery may be performed to relieve them. A tendon release procedure, also called heel cord surgery, is often done to treat ankle and other contractures while the child is still walking. Usually the boy will need to wear lower leg braces after this.

Diet

No special dietary restrictions or additions are known to help in DMD. Most doctors recommend a diet similar to that for any growing boy but with a few modifications.

A combination of immobility and weak abdominal muscles can lead to severe constipation, so the diet should be high in fluid and fiber, with fresh fruits and vegetables dominant.

For boys who use power wheelchairs, take prednisone or who aren’t very active, excessive weight gain can become a problem. For these boys, caloric intake should probably be somewhat restricted to keep weight down. Obesity puts greater stress on already weakened skeletal muscles and the heart. Doctors have found that a low-calorie diet doesn’t have any harmful effect on the muscles.

Those on prednisone and those with heart problems may need a sodium-restricted diet.

Also see:

• Nutritional Considerations While on Corticosteroids (includes meal planning guides and suggested food options)

Exercise

Exercise can help build skeletal muscle, keep the cardiovascular system healthy, and contribute to feeling better. But in muscular dystrophy, too much exercise could damage muscle. Consult with your doctor about how much exercise is best. A person with DMD can exercise moderately but shouldn’t go to the point of exhaustion.

Many experts recommend swimming and water exercises (aquatic therapy) as a good way to keep muscles as toned as possible without causing undue stress on them. The buoyancy of the water helps protect against certain kinds of muscle strain and injury.

Before undertaking any exercise program, make sure to have a cardiac evaluation.

Learning disabilities

Children with DMD who are suspected of having a learning disability can be evaluated by a developmental or pediatric neuropsychologist through the school system’s special education department or at a medical center with a referral from the MDA clinic.

If a learning disability is diagnosed, educational and psychological interventions can begin right away. The specialist may prescribe exercises and techniques, and the school also can provide special help with learning.

Also see:

• When Neuromuscular Disease Affects the Brain

• The Brain in Duchenne Muscular Dystrophy: Are learning disabilities part of the picture?

• A Teacher's Guide to Neuromuscular Disease

Medications

Medications that lessen the workload on the heart are sometimes prescribed for DMD (See cardiac care, above).

Medications belonging to a group known as corticosteroids have been found effective in slowing the course of DMD. The corticosteroids prednisone (available in the United States) and deflazacort (not usually available in the United States) are beneficial in the treatment of DMD.

Several high-quality studies of these medications in DMD showed a significant increase in strength, timed muscle function (such as the time it took to climb stairs) and pulmonary function.

Physical and occupational therapy

A physical therapy program is usually part of the treatment for DMD. Your MDA clinic physician will refer you to a physical therapist for a thorough evaluation and recommendations. The primary goals of physical therapy are to allow greater motion in the joints and to prevent contractures and scoliosis.

While physical therapy emphasizes mobility and, where possible, strengthening of large muscle groups, occupational therapy focuses on specific activities and functions. Occupational therapy can help with tasks for work, recreation or daily living, such as dressing or using a computer.

Respiratory care

As the muscles that assist in breathing get weaker, the bronchial system must be kept free of secretions, either by using a cough assist device or by manual assisted coughing with the help of a caregiver. A respiratory therapist or pulmonologist can be consulted for the needed information. At some point, assisted ventilation may be needed to help provide sufficient air flow into and out of the lungs.

The first step in using assisted ventilation is usually a noninvasive device, meaning one that doesn’t require any surgical procedures. The person receives air under pressure through a mask, nosepiece or mouthpiece. Noninvasive ventilation usually is required only part time, often only during sleep.

If round-the-clock ventilatory support becomes necessary, it’s possible to use noninvasive ventilation full time, under the care of a doctor knowledgeable in this practice. Some young men choose to switch to an invasive system, which means that a surgical opening called a tracheostomy is performed, allowing air to be delivered directly into the trachea (windpipe).

For more, see:

• Getting a Tracheostomy: My Story (a physician with mitochondrial myopathy describes undergoing and taking care of her tracheostomy)

• The Great Trach Escape: Is it for You? (portable but powerful equipment, skilled guidance make noninvasive ventilation an option for many)

Spinal curvatures

In young men with DMD, the spine can be gradually pulled into a curved shape. The spine may curve from side to side (scoliosis) or forward in a “hunchback” shape (kyphosis).

Scoliosis usually appears after a boy has started using a wheelchair full time. The “swayback” curvature that's sometimes seen in those who are still walking is called lordosis.

Severe scoliosis can interfere with sitting, sleeping and even breathing, so measures should be taken to try to prevent it.

Exercises to keep the back as straight as possible and advice about sitting and sleeping positions can be obtained from a physical therapist.

Spine-straightening surgery involves inserting metal rods with hooks into the spine.

Surgery for youngsters with DMD is usually performed in adolescence.

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