Muscular dystrophies are a group of genetic disorders that result in progressive muscle weakness. Clinicians can use several tests to help diagnose muscular dystrophy.
A correct diagnosis gives patients an understanding of how their disease is likely to progress and helps to inform the treatments and supportive strategies used to manage the symptoms. Diagnosing the more common forms of muscular dystrophy tends to be easier because their recognizable sets of symptoms are likely to prompt doctors to look for genetic defects associated with those forms.
Although a number of diagnostic tools can point toward muscular dystrophy, genetic testing is usually the most accurate way to diagnose the disease.
Genetic testing involves analyzing a person’s DNA to look for mutations known to cause muscular dystrophy. It can be done to help diagnose someone who is experiencing symptoms or to identify people at risk of developing the disease or passing it to their biological children.
Often one of the first tests done when muscular dystrophy is suspected is to look for markers of muscle damage, such as creatinine kinase and aldolase, in the blood. Elevated levels of these proteins suggest muscle damage, and muscular dystrophy patients typically have levels well above what is normal, especially in earlier stages of disease.
Electromyography (EMG) is a diagnostic procedure that measures the electrical activity in muscles. For a muscle to contract, an electrical signal passes from a nerve cell and through the muscle cell. These signals are measured as a change in potential, or in voltage.
EMG typically involves inserting a small needle, called an electrode, into the muscle tissue. The electrode records the electrical activity in muscles when they’re at rest and when they contract during movement.
The electrical activity is displayed in real time in the form of waves on a device called an oscilloscope and may also be heard through a speaker. Normally, a more forceful muscle contraction results in more electrical activity in the muscles and, consequently, a larger wave on the oscilloscope.
EMG is often done at the same time as a similar test called a nerve conduction study. This procedure is done with electrodes placed on the skin, and as its name suggests, it measures electrical activity in nerve cells. Doing both procedures can be useful for determining whether muscle weakness is caused by problems with nerves or with muscles.
Magnetic resonance imaging
Magnetic resonance imaging, or MRI, is a technique that uses a magnetic field and radio waves to produce detailed images of the inside of the body.
People with muscular dystrophy typically have a higher-than-normal concentration of fat in their muscles. MRIs help clinicians understand which muscle is affected most by MD and can inform the choice of a suitable muscle for a biopsy, if needed.
In addition to initial diagnoses, muscle MRIs are used to follow the course of a patient’s disease as it progresses. MRI scans over time help clinicians track the amount of fat infiltrating muscle tissue, which tends to correlate with changing muscle strength and function.
A muscle biopsy is when clinicians remove a small piece of muscle tissue, which is then sent to a laboratory for analysis. These analyses can help to identify biochemical and physical changes in muscle cells that are indicative of muscular dystrophy, and they can aid in ruling out other conditions.
Depending on the specific muscle and the amount of tissue needed, biopsies may be collected either with a needle inserted through the skin or by making a cut through the skin.
Six-minute walk test
The six-minute walk test (sometimes abbreviated 6MWT) is simply a measure of how far a person is able to walk in six minutes on a flat, hard surface. This test is commonly used to assess physical function and exercise capacity in individuals who are able to walk and may be useful for monitoring changes in function over time.
Last updated: Nov. 29, 2021
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