Duchenne Muscular Dystrophy (DMD)
In diagnosing any form of muscular dystrophy, a doctor usually begins by taking a patient and family history, and performing a physical examination. Much can be learned from these, including the pattern of weakness. The history and physical go a long way toward making the diagnosis, even before any complicated diagnostic tests are done.
Early in the diagnostic process, doctors often order a blood test called a CK level. CK stands for creatine kinase, an enzyme that leaks out of damaged muscle. When elevated CK levels are found in a blood sample, it usually means muscle is being destroyed by some abnormal process, such as a muscular dystrophy or inflammation. A very high CK level suggests that the muscles themselves (and not the nerves that control them) are the likely cause of the weakness, although it doesn’t tell exactly what the muscle disorder might be.
Genetic testing involves analyzing the DNA of any cells (usually blood cells are used) to see whether there is a mutation in the dystrophin gene, and if so, exactly where it occurs. Such DNA testing for dystrophin mutations is widely available in the United States. Ask your MDA clinic physician or genetic counselor for more information. And, for more on getting a definitive genetic diagnosis, see The Genie's Out of the Bottle: Genetic testing in the 21st century.
Female relatives of men and boys with DMD can undergo DNA testing to see if they are carriers of the disease. Women who are DMD carriers can pass on the disease to their sons and their carrier status to their daughters. In a minority of cases, girls and women who are DMD carriers may themselves show symptoms of DMD, such as muscle weakness and heart problems. These symptoms may not show up until adulthood. (See Causes/Inheritance.)
Several experimental drugs currently in development to treat DMD require knowledge of the person's precise genetic mutation, so genetic testing has become important not only for diagnosis but possibly for future treatments.
To obtain more information, the doctor may order a muscle biopsy, the surgical removal of a small sample of muscle from the patient. By examining this sample, doctors can tell a great deal about what’s actually happening inside the muscles.
Modern techniques can use the biopsy to distinguish muscular dystrophies from inflammatory and other disorders, and also to distinguish among different forms of muscular dystrophy. For instance, the amount of functional dystrophin protein found in a muscle biopsy sample sheds light on whether the disease course is likely to be DMD (with no dystrophin present) or the milder Becker muscular dystrophy (with some partially functional dystrophin present).