What You Should Know About Muscle Biopsies

Weakness can be caused by disorders of the brain, spinal cord, peripheral nerves, neuromuscular junction, or the muscle itself.  There are many different kinds of muscle diseases.

In order to correctly diagnose the problem and thereby offer appropriate treatment, sometimes a piece of muscle has to be obtained in order to look at affected muscle under a microscope. Sometimes, in fact, more than one sample may be needed, as some muscle diseases don’t involve the entire body, but instead have a patchy distribution. 

How a Muscle Biopsy Is Done

There are two main forms of muscle biopsy. The first involves a biopsy needle being inserted through the skin into a muscle, which takes a small sample. Alternatively, an incision can be made in the skin to view and cut muscle directly. The latter approach is called an “open biopsy.” While open biopsies are a bit more involved, they may allow for more sample selection in the case of patchy muscle disorders.  Regardless of the technique, only a small amount of tissue needs to be removed. 

The site of the muscle biopsy depends on the location of symptoms like weakness or pain. Common locations include the thigh, biceps or shoulder muscle. 

Who Needs a Muscle Biopsy?

People with weakness and low muscle tone may be considered for muscle biopsy, but it’s not usually the first step. Other evaluations such as nerve conduction studies or electromyography may be done first to determine if the cause is truly in the muscle itself.

Uses

Muscle diseases include several types of muscular dystrophies, meaning a genetic disorder that causes muscle breakdown. Some common types include Duchenne and Becker’s muscular dystrophy.

Myositis means inflammation of the muscle, which may also be identified under the microscope. Examples include polymyositis and dermatomyositis.

Muscle biopsy can also identify certain infections, like trichinosis or toxoplasmosis.

This list offers some examples but is not complete. Healthcare providers may also order a muscle biopsy for other reasons.

Risks

Muscle biopsy is generally considered a safe and minor surgical procedure. However, there are some risks. The most common complications include bruising or pain at the site of the biopsy. Prolonged bleeding or even infection is also possible, requiring practitioners to take precautions to avoid such complications. You should inform your healthcare provider if you are on any blood-thinning medications or have a history of a bleeding disorder.

During the Procedure

While there’s some variation in how different healthcare providers perform muscle biopsies, in general you can expect the following:

• You will be asked to remove your clothing around the site of the biopsy.
• You will be asked to lie still during the procedure.
• The skin will be cleaned.
• A local injection of pain medication will be given to numb the area. You may feel an initial sting and burning sensation with the numbing medication.
• Either a biopsy needle will be inserted, or the healthcare provider will use a scalpel to make a small cut through the skin, and small pieces of muscle will be removed using surgical scissors.
• The opening will be closed with stitches if necessary. 
• A sterile bandage will be applied.

After the Procedure

You should keep the biopsy area clean and dry. Some tenderness is common for a few days after the biopsy. Take medication as suggested by your practitioner for pain. Be sure to contact your healthcare provider if you develop signs of infection like fever, redness, or drainage from the biopsy site. Also, let them know if you have worsening pain or bleeding.

What Happens to the Muscle Sample

The muscle will be looked at with different techniques under the microscope. Different chemicals are used to identify signs of different diseases. For example, hematoxylin and eosin are useful for identifying inflammatory diseases, Gomori trichrome stain is good for identifying inclusion body myositis, cytochrome oxidase can identify mitochondrial diseases, and periodic acid Schiff stains can identify glycogen and carbohydrate storage disorders. What tests are used will depend on your healthcare provider’s suspicions on the underlying cause of the disease.

A muscle biopsy is not always the last step in diagnosis. For example, different types of diseases may appear similar under the microscope. For example, in some cases, genetic testing may be needed. Even when muscle biopsy is not the final step, however, it can guide the ordering of additional tests that will confirm a more specific diagnosis.