What Is Muscular Dystrophy?
Muscular dystrophy (MD) is a group of inherited diseases in which the muscles that control movement (called voluntary muscles) progressively weaken. In some forms of this disease, the heart and other organs are also affected.
There are nine major forms of muscular dystrophy:
Muscular dystrophy can appear in infancy up to middle age or later, and its form and severity are determined in part by the age at which it occurs. Some types of muscular dystrophy affect only males; some people with MD enjoy a normal life span with mild symptoms that progress very slowly; others experience swift and severe muscle weakness and wasting, dying in their late teens to early 20s.
The various types of MD affect more than 50,000 Americans. Through advances in medical care, children with muscular dystrophy are living longer than ever before.
Muscular Dystrophy Symptoms by Type
- Myotonic (also called MMD or Steinert's disease). The most common form of muscular dystrophy in adults, myotonic muscular dystrophy affects both men and women, and it usually appears any time from early childhood to adulthood. In rare cases, it appears in newborns (congenital MMD). The name refers to a symptom, myotonia -- prolonged spasm or stiffening of muscles after use. This symptom is usually worse in cold temperatures. The disease causes muscle weakness and also affects the central nervous system, heart, gastrointestinal tract, eyes, and hormone-producing glands. In most cases, daily living isn't restricted for many years. Those with myotonic MD have a decreased life expectancy.
- Duchenne. The most common form of muscular dystrophy in children, Duchenne muscular dystrophy affects only males. It appears between the ages of 2 and 6. The muscles decrease in size and grow weaker over time yet may appear larger. Disease progression varies, but many people with Duchenne (1 in 3,500 boys) need a wheelchair by the age of 12. In most cases, the arms, legs, and spine become progressively deformed, and there may be some cognitive impairment. Severe breathing and heart problems mark the later stages of the disease. Those with Duchenne MD usually die in their late teens or early 20s.
- Becker. This form is similar to Duchenne muscular dystrophy, but the disease is much milder: symptoms appear later and progress more slowly. It usually appears between the ages of 2 and 16 but can appear as late as age 25. Like Duchenne muscular dystrophy, Becker muscular dystrophy affects only males (1 in 30,000) and causes heart problems. Disease severity varies. Those with Becker can usually walk into their 30s and live further into adulthood.
- Limb-girdle. This appears in the teens to early adulthood and affects males and females. In its most common form, Limb-girdle muscular dystrophy causes progressive weakness that begins in the hips and moves to the shoulders, arms, and legs. Within 20 years, walking becomes difficult or impossible. Sufferers typically live to middle age to late adulthood.
- Facioscapulohumeral. Facioscapulohumeral refers to the muscles that move the face, shoulder blade, and upper arm bone. This form of muscular dystrophy appears in the teens to early adulthood and affects males and females. It progresses slowly, with short periods of rapid muscle deterioration and weakness. Severity ranges from very mild to completely disabling. Walking, chewing, swallowing, and speaking problems can occur. About 50% of of those with facioscapulohumeral MD can walk throughout their lives, and most live a normal life span.
- Congenital. Congenital means present at birth. Congenital muscular dystrophies progress slowly and affect males and females. The two forms that have been identified -- Fukuyama and congenital muscular dystrophy with myosin deficiency -- cause muscle weakness at birth or in the first few months of life, along with severe and early contractures (shortening or shrinking of muscles that causes joint problems). Fukuyama congenital muscular dystrophy causes abnormalities in the brain and often seizures.
- Oculopharyngeal. Oculopharyngeal means eye and throat. This form of muscular dystrophy appears in men and women in their 40s, 50s, and 60s. It progresses slowly, causing weakness in the eye and face muscles, which may lead to difficulty swallowing. Weakness in pelvic and shoulder muscles may occur later. Choking and recurrent pneumonia may occur.
- Distal. This group of rare diseases affects adult men and women. It causes weakness and wasting of the distal muscles (those farthest from the center) of the forearms, hands, lower legs, and feet. It is generally less severe, progresses more slowly, and affects fewer muscles than other forms of muscular dystrophy.
- Emery-Dreifuss. This rare form of muscular dystrophy appears from childhood to the early teens and affects mainly males. In very rare cases, females can be affected. For that to happen, both of a girls X chromosomes (the one she gets from her mother and the one from her father) would have to have the defective gene. It causes muscle weakness and wasting in the shoulders, upper arms, and lower legs. Life-threatening heart problems are common and can also affect carriers -- those who have the genetic information for the disease but do not develop the full-blown version (including mothers and sisters of those with Emery-Dreifuss MD). Muscle shortening (contractures) occurs early in the disease. Weakness can spread to chest and pelvic muscles. The disease progresses slowly and causes less severe muscle weakness than some other forms of muscular dystrophy.
Muscular Dystrophy Causes and Risk Factors
Muscular dystrophy is caused by defects in certain genes, with type determined by the abnormal gene. In 1986, researchers discovered the gene that, when defective or flawed, causes Duchenne muscular dystrophy. In 1987, the muscle protein associated with this gene was named dystrophin. Duchenne muscular dystrophy occurs when that gene fails to make dystrophin. Becker muscular dystrophy occurs when a different mutation in the same gene results in some dystrophin, but it's either not enough or it's poor in quality. Scientists have discovered and continue to search for the genetic defects that cause other forms of muscular dystrophy.
Most of the muscular dystrophies are a form of inherited disease called X-linked disorders or genetic diseases that mothers can transmit to their sons even though the mothers themselves are unaffected by the disease.
Men carry one X chromosome and one Y chromosome. Females carry two X chromosomes. Thus, in order for a girl to become affected by muscular dystrophy, both of her X chromosomes would have to carry the defective gene -- an extremely rare occurrence, since her mother would have to be a carrier (one defective X chromosome) and her father would have to have muscular dystrophy (since men carry just one X chromosome, the other is a Y chromosome).
A female who carries the defective X chromosome can pass the disease to her son (whose other chromosome is a Y, from the father).
A few muscular dystrophies aren't inherited at all and occur because of a new gene abnormality or mutation.
Muscular Dystrophy Diagnosis
To start, your doctor will examine your child and ask questions about medical and family health history. Muscular dystrophy is diagnosed using several different tests. These may include:
Muscle biopsy. A small piece of muscle tissue is removed and examined to confirm the diagnosis or rule out another muscle disease.
Neurological tests. Various tests are done to check nervous system function, reflexes, and coordination. One example is a nerve conduction study, also called a nerve function test, or electromyography (EMG).
Enzyme tests. These are blood tests that check for proteins, or enzymes, linked to muscle weakness. People with muscular dystrophy have high levels of the enzyme creatine kinase. It’s made when muscles are damaged. They also have higher levels of serum aldolase, which is made when your body breaks down sugar into energy.
Heart monitoring. An electrocardiogram may be done to check for an abnormal heartbeat. Some types of muscular dystrophy cause irregular heartbeats.
Muscular Dystrophy Treatment
There is no cure for muscular dystrophy, but treatments can help manage symptoms and improve quality of life.
Prescription drugs are available to control muscular dystrophy symptoms or slow their progression. Medications for muscular dystrophy include:
- Steroids. Corticosteroids, such as prednisone and deflazacort (Emflaza), are the standard of care for muscular dystrophy. They help improve muscle strength and breathing and decrease weakness. Side effects include high blood pressure and weight gain. People who use steroids for a long time are at risk for brittle bones.
- Medicines targeting gene mutations. Eteplirsen (Exondys 51) and golodirsen (Vyondys 53) increase the level of the gene dystrophin. They’re approved to specifically treat Duchenne muscular dystrophy.
- Anticonvulsants. Often used to treat epilepsy, these antiseizure drugs may also help reduce muscle spasms.
- Immunosuppressants. These powerful medicines are often used to treat lupus and other autoimmune diseases. When given to people with muscular dystrophy, they may help prevent some muscle cell damage.
- Antibiotics. The doctor may prescribe an antibiotic to treat a lung infection, which is common in people with muscular dystrophy.
Physical therapy helps keep joints and muscles flexible. It’s an important part of a muscular dystrophy treatment plan.
The goal of physical therapy is to improve strength in the large muscle groups and prevent scoliosis and contractures.
Physical therapy for muscular dystrophy may involve:
Muscle weakness can affect the lungs, making breathing difficult. A respiratory therapist can teach you and your child how to properly use a mask, nose device, or mouthpiece.
Mobility and positioning aids
Braces, walkers, or wheelchairs help provide mobility and independence to people with muscular dystrophy. Standing with a walker, even for just a little bit each day, boosts blood flow and helps build better bones.
Muscle weakness in the face and throat can make speaking difficult. Learning how to properly pace breathing and talking can be helpful. A speech therapist can also show you how to use speech communication devices.
Surgery may be recommended to manage or correct complications of muscular dystrophy. For example, cataract surgery may be done to replace a cloudy eye lens. Or a person with muscular dystrophy may need spinal fusion surgery to treat scoliosis, or heart surgery to implant a pacemaker.
Muscular Dystrophy Complications
The complications of muscular dystrophy depend on the type. Some types are mild, while others are serious and get worse very fast. Worsening muscle weakness can affect the ability to walk, breathe, swallow, and speak.
Complications of muscular dystrophy can include:
Breathing problems. Progressive weakness in the breathing muscles (diaphragm) makes it hard to take a breath. That raises the risk for lung infections such as pneumonia.
Curving of the spine (scoliosis). Weakness in the muscles supporting the backbone causes the spine to become curved. Most people with Duchenne muscular dystrophy need scoliosis surgery.
Heart problems. Some types of muscular dystrophy cause abnormal and dangerous changes in the heartbeat. You need a pacemaker to regulate it. Muscular dystrophy can also cause the heart muscle to become weak (cardiomyopathy). That leads to heart failure.
Swallowing difficulty. Weakness affects the muscles in the esophagus, and causes problems with chewing and swallowing. This can lead to choking. Some people with muscular dystrophy will need a feeding tube.
Shortening of the tendons or muscles around the joints (contractures). Bracing and tendon release surgery can help prevent some contractures.
Need for a wheelchair. Weakness in the large muscles of the legs makes it difficult to walk, stand, kneel, or climb. Some people with muscular dystrophy eventually need to use a wheelchair.