A muscle biopsy is a procedure that removes a small sample of tissue for testing in a laboratory. The test can help your doctor see if you have an infection or disease in your muscles.

A muscle biopsy is a relatively simple procedure. It’s usually done on an outpatient basis, which means you’ll be free to leave on same day as the procedure. You may receive local anesthesia to numb the area from which the doctor is removing tissue, but you’ll remain awake for the test.

A muscle biopsy is performed if you are experiencing problems with your muscle and your doctor suspects an infection or disease could be the cause. The biopsy can help your doctor rule out a certain condition as a cause of your symptoms. It can also help them make a diagnosis and initiate a treatment plan.

Your doctor may order a muscle biopsy for various reasons. They may suspect you have:

  • defects in the way your muscles metabolize, or use energy
  • diseases that affect blood vessels or connective tissue, such as polyarteritis nodosa (which causes the arteries to become swollen)
  • infections related to the muscles, such as trichinosis (an infection caused by a type of roundworm)
  • muscular disorders, including types of muscular dystrophy (genetic disorders that lead to muscle weakness and other symptoms)

Your doctor might use this test to tell if your symptoms are being caused by one of the muscle-related conditions above, or by a problem with your nerves.

Any medical procedure that breaks the skin carries some risk of infection or bleeding. Bruising is also possible. However, since the incision made during a muscle biopsy is small — especially in needle biopsies — the risk is much lower.

Your doctor will not take a biopsy of your muscle if it was recently damaged in another procedure — for instance, by a needle during an electromyography (EMG) test — or if it’s already known to have nerve damage.

There’s a small chance of damage to the muscle where the needle enters, but this is rare. Always talk with your doctor about any risks before a procedure and share your concerns.

You don’t need to do much to prepare for this procedure. Depending on the type of biopsy you will have, your doctor may give you some instructions to carry out before the test. These instructions typically apply to open biopsies.

Prior to a procedure, it’s always a good idea to tell your doctor about any prescription drugs, over-the-counter medications, herbal supplements, and especially blood thinners (including aspirin) you are taking. Discuss with them whether you should stop taking the medication before and during the test, or if you should change the dosage.

There are two different ways to perform a muscle biopsy.

The most common method is called a needle biopsy. For this procedure, your doctor will insert a thin needle through your skin to remove your muscle tissue. Depending on your condition, the doctor will use a certain type of needle. These include:

  • Core needle biopsy. A medium-sized needle extracts a column of tissue, similar to the way core samples are taken from the earth.
  • Fine needle biopsy. A thin needle is attached to a syringe, allowing fluids and cells to be drawn out.
  • Image-guided biopsy. This kind of needle biopsy is guided with imaging procedures — like X-rays or computed tomography (CT) scans — so your doctor can avoid specific areas like your lungs, liver, or other organs.
  • Vacuum-assisted biopsy. This biopsy uses suction from a vacuum to collect more cells.

You will receive local anesthesia for a needle biopsy and should not feel any pain or discomfort. In some cases, you may feel some pressure in the area where the biopsy is being taken. Following the test, the area may be sore for about a week.

If the muscle sample is hard to reach — as may be the case with deep muscles, for instance — your doctor may choose to perform an open biopsy. In this case, your doctor will make a small cut in your skin and remove the muscle tissue from there.

If you’re having an open biopsy, you may receive a general anesthesia. This means you will be sound asleep throughout the procedure.

After the tissue sample is taken, it’s sent to a laboratory for testing. It could take up to a few weeks for the results to be ready.

Once the results are back, your doctor may call you or have you come to their office for a follow-up appointment to discuss the findings.

If your results come back abnormal, it could mean you have an infection or disease in your muscles that may be causing them to weaken or die. Your doctor may need to order more tests to confirm a diagnosis or see how far the condition has progressed. They will discuss your treatment options with you and help you plan your next steps.