A muscle biopsy takes a small sample of muscle to look at under the microscope. It is often the clearest way to confirm which type of myositis you have.
You stay awake. Plan for about 30 to 45 minutes, plus a short rest afterward.
A muscle biopsy is a minor procedure to remove a small piece of muscle, usually from the thigh, upper arm, or shoulder. The sample is sent to the laboratory and examined under a microscope by specialists. Your team chooses a muscle that is affected by the disease but still working, often guided by your examination, your EMG, or an MRI scan.
There are two ways it may be done. A needle biopsy takes a small sample through a tiny nick in the skin. An open biopsy uses a small cut to take a slightly larger sample, which is then closed with a few stitches or skin strips.
Looking at the muscle directly lets the team see inflammation, muscle-fibre damage, and specific patterns that point to a particular type of myositis, such as inclusion body myositis. It can confirm the diagnosis when blood tests and other tests are not enough, and it helps rule out other muscle diseases, so your treatment is based on the right answer.
Muscle samples take time to process, and some tests are sent to specialised laboratories, so results can take from several days to a few weeks. Your team will explain what the biopsy shows and what it means for your treatment.
This guide is for learning, not medical advice. Your team will explain your own test, and every person’s situation is a little different. Always follow the instructions you are given.