Muscular dystrophy is a group of genetic diseases that cause progressive weakness of the body's muscles. Some types of muscular dystrophy will present symptoms in early childhood, while other types will appear in adulthood. Different muscle groups also may be affected depending on the type of muscular dystrophy.
Duchenne muscular dystrophy is the most common form of childhood muscular dystrophy. It generally appears in 3-to 6-year-old boys and worsens rapidly.
Becker muscular dystrophy has symptoms similar to Duchenne muscular dystrophy. However, symptoms most commonly begin in the teens to mid-20s and progress slowly.
Different types of muscular dystrophy begin to show symptoms at different ages and, depending on the type of muscular dystrophy, different muscle groups throughout the body will be affected.
Symptoms may include:
- Progressive muscle weakness and wasting (atrophy)
- Waddling way of walking
- Difficulty climbing stairs
- Difficulty rising from lying or sitting
- Repeated falling
- Curvature of the spine
- Wasting of thigh muscles
- Abnormal enlargement of the calves
- Trouble breathing or swallowing
- Limbs drawing inward and becoming fixed in position
- Enlargement of the heart
In addition to Duchenne and Becker muscular dystrophies, there are other less common types:
- Facioscapulohumeral muscular dystrophy (FSHD or Landouzy-Dejerine syndrome), which affects mainly facial, shoulder and arm muscles
- Limb-girdle muscular dystrophy, first affecting hips and shoulders
- Myotonic muscular dystrophy (MMD or Steinert's disease), which causes the inability to relax muscles and generally affects facial muscles first
- Oculopharyngeal muscular dystrophy, typically occurring in middle age with weakness of eye, face and throat muscles causing drooping eyelids and issues with swallowing
Causes and Risk Factors
Defective genes are the cause of muscular dystrophy. The specific gene disorder has been discovered for the most common muscular dystrophies. For example, a defective gene for dystrophin, a protein that helps keep muscle cells intact, is what causes Duchenne's muscular dystrophy.
For the less common forms of muscular dystrophy, researchers are still trying to find the specific gene defect that causes the disease. While most forms of muscular dystrophy are inherited, a few types originate in a spontaneous gene mutation without any family history of the disease.
To diagnose any form of muscular dystrophy, a physician will take a thorough medical history and perform a physical examination. Some diagnostic tests also may be ordered.
A blood test will show if the enzyme creatine kinase is leaking from the muscle cells, causing abnormally high levels in the blood. While high blood levels of creatine kinase don’t necessarily confirm that a patient has muscular dystrophy, it is an indication of muscle disease.
Electromyography and nerve conduction studies measure electrical activity of muscle and nerve function to detect the presence, location and extent of diseases that can damage muscle tissue.
A muscle biopsy - in which a small piece of the muscle is removed for examination under a microscope - is usually taken in order to confirm the condition. Under the microscope, the muscle of a positive biopsy generally shows dead tissue and abnormally large muscle fibers. In the late stages of muscular dystrophy, fat and other tissues replace the dead muscle tissue.
Genetic testing can be performed to determine the gene mutations that caused muscular dystrophy.
Currently, there is no known cure for any of the muscular dystrophies. Physical therapy and exercise help prevent muscles from contracting permanently around joints and avoid curvature of the spine. Sometimes surgery is needed to release tight, painful muscles. Breathing exercises can help delay weakening of the respiratory muscles.
Some symptoms can be treated, and progression may be slowed with medications. Prednisone, a powerful corticosteroid drug, is currently used to temporarily relieve muscle weakness and slow muscle damage, as well as help with respiratory function. For some types of muscular dystrophy, heart problems may arise that can be treated with medication or a pacemaker.
Researchers are looking into gene therapy that would enable muscles to produce dystrophin (for Duchenne and Becker muscular dystrophies), as well as other therapies to find a cure for all the muscular dystrophies.