Muscular dystrophy (MD), covering a group of genetic disorders that cause progressive weakness and loss of muscle mass, can be diagnosed through procedures that may include a physical exam, blood and other laboratory tests, genetic tests, electromyography, imaging scans, and muscle biopsy.
Blood samples are often taken early in cases of suspected muscular dystrophy, because they are a relatively easy way to begin working toward a diagnosis. Blood serum samples are used to check for the levels two enzymes known as creatine kinase and as aldolase, which can signal a muscular disorder exists and further testing is warranted, and blood cell samples are used for genetic testing.
Creatine kinase (CK) is an enzyme that exists in skeletal and heart muscle, in the brain and in other tissues. CK blood levels can rise due to many causes — a heart attack, traumatic muscle damage, infections, celiac disease, even intense exercise — because the enzyme leaks from muscle that’s been damaged, as in MD. High levels of CK in the blood signal muscle destruction that could be due to muscular dystrophy or to inflammation; they show that skeletal muscles are the reason for muscular weakness, but do not pinpoint the underlying disorder or cause.
In early stages of MD, CK levels are much higher than in later stages, because muscle degeneration is more rapid in earlier stages and, possibly, because of declines in muscle mass in a patient.
CK levels are particularly elevated in certain types of MD, such as Duchenne MD, and less elevated in others like Becker MD. In Duchenne, CK blood levels can be 10 to 200 times above normal, which is considered 60 to 400 units/liter.
CK levels can help to confirm a suspected muscular problem before disease symptom are evident.
Aldolase is an enzyme that helps break down sugars to produce energy.
Higher than normal aldolase levels can indicate muscle disease, and these levels are usually checked in cases of suspected MD.
As with CK, the highest levels of aldolase are found in Duchenne MD, and the increase in aldolase becomes less significant as the disease progresses.
A blood sample is frequently used for genetic testing to detect the specific mutations — or changes to a gene — that cause a specific type of muscular dystrophy. Knowing the type of MD in a patient is crucial to determining proper care.
Types of genetic testing can vary. But all genetic tests can confirm an MD diagnosis and help to identify the particular type of MD in a patient.
Genetic testing are also used to inform carriers — people who have the disease-causing mutation but no disease symptoms, but can pass the disease to children — and be of use in disease research.
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