Depending on the results of other lab tests, your doctor may order a muscle biopsy. The biopsy is one of the best ways to diagnose myositis and other muscle disorders.
MRI scans of muscles may be helpful in selection of a site for muscle biopsy in patients with suspected inflammatory myopathy when a first muscle biopsy turns out to be negative.
For this test, a doctor will remove a piece of your muscle tissue and study it under a microscope for abnormalities.
How is a muscle biopsy done?
A muscle biopsy can usually be done under local anesthesia (numbness to a specific area). A needle biopsy may be used for children and for adults with chronic conditions. The doctor puts a needle into your muscle and removes a small piece of tissue. Watch a video of a needle biopsy.
Other times an open biopsy is needed, where a wider area is sampled. This is the same test but requires cutting the skin to get to the muscle tissue.
Your doctor will choose the muscle depending on where you are feeling the pain and weakness. Most likely, he or she will avoid muscles already tested by a recent EMG or muscle biopsy. MRI's are now widely used to locate affected muscles to biopsy.
Will it hurt?
There is usually little or no pain with this test but instead an uncomfortable tugging feeling. However, some people report more pain depending on the size of the muscle sample taken. If you have an open biopsy, you may feel more pain than with a needle biopsy because of the amount of muscle tissue removed.
If you are explaining this test to a child, you may say that the needle can hurt a little and they may feel sore the next day. There may be bleeding at the site. A mild pain may last for about a week, and you may see a bruise. Ask the doctor about controlling this pain for yourself or your child.
What are the risks of having this test?
There are few risks with this test. Any time your skin is broken, there is a small risk of infection at that spot. There also may be some bleeding or bruising.
What do the results of this test mean?
If the doctor sees something unusual about the muscle that was tested, he or she will run as many tests on that muscle as necessary to decide what type of muscle condition you may have. The results can show conditions such as inflammation, or swelling, of the muscle; damage to the muscle; and loss of muscle mass, or atrophy.
Be sure to talk to your doctor about any questions or concerns you may have before and after the muscle biopsy.
To better understand the skin symptoms related to dermatomyositis, doctors may take a skin biopsy. The doctors remove a small piece of skin by first numbing the area with an injection of local anesthetic and then "scraping" the skin with a special device. They study the skin under a microscope for specific features to help them diagnose and treat the skin manifestations of the disease.
The biopsied area should heal within a week or two.
Watch a video of a skin biopsy.
Updated March 2012