This group of diseases usually causes weakness in the muscles closest to the torso (mid-section of the body). There are several kinds, with the most common being Duchenne's muscular dystrophy.
Duchenne's muscular dystrophy is an inherited disease of skeletal (voluntary) muscles and the most common form of childhood muscular dystrophy. It generally appears from age three to six years and worsens rapidly.
At first, muscle weakness and wasting within the pelvic (hipbone) area occurs followed by similar problems in the shoulder muscles. Eventually, muscle weakness and wasting affect the trunk and forearms then spread to other major muscles of the body.
Other less common forms of muscular dystrophy are facioscapulohumeral muscular dystrophy (FSHD or Landouzy-Dejerine syndrome, affecting mainly facial, shoulder and arm muscles), limb-girdle muscular dystrophy and myotonic dystrophy.
Depending on the type, symptoms of muscular dystrophy may include a waddling way of walking; difficulty climbing stairs or rising from sitting; and repeated falling. As the disease worsens, other abnormalities may develop, such as curvature of the spine, wasting of thigh muscles, abnormal enlargement of the calves and enlargement of the heart.
Causes and Risk Factors
Defective genes are the cause of muscular dystrophy. The specific gene disorder is known for most common muscular dystrophies. There are many less common forms where the specific defect needs to be discovered. A family history of the condition is often, but not always present.
Doctors suspect muscular dystrophy when a young boy becomes weak and grows weaker. An enzyme (creatinine kinase) leaks out of muscle cells, causing enzyme levels in the blood to be abnormally high. However, high blood levels of creatinine kinase don't necessarily mean that a person has muscular dystrophy. Other muscle diseases may also cause high levels of this enzyme.
A doctor usually takes a muscle biopsy - in which a small piece of the muscle is removed for examination under a microscope - to be sure of the diagnosis. Under the microscope, the muscle 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.
Duchenne's muscular dystrophy is diagnosed when special tests show extremely low levels of the protein dystrophin in the muscle. Other tests given may include electrical studies of muscle function (electromyography) and nerve conduction studies.
There is currently no known cure for any of the muscular dystrophies. However, physical therapy and exercise help prevent muscles from contracting permanently around joints. Sometimes surgery is needed to release tight, painful muscles.
Prednisone, a powerful steroid drug, is being often used as a way to temporarily relieve the muscle weakness in Duchenne's muscular dystrophy. Also under investigation is gene therapy that would enable muscles to produce dystrophin and other gene defects.