A muscle biopsy is the removal of a small piece of muscle tissue for examination.

How the Test is Performed

This procedure is usually done while you are awake. Your health care provider will apply a numbing medicine (local anesthesia) to the biopsy area.

There are two types of muscle biopsy:

• A needle biopsy involves inserting a needle into the muscle. When the needle is removed, a small piece of tissue remains in the needle. More than one needle stick may be needed to get a large enough sample.
• An open biopsy involves making a small cut in the skin and into the muscle. The muscle tissue is then removed.

After either type of biopsy, the tissue is sent to a lab for examination.

How to Prepare for the Test

No special preparation is usually needed. If you will have anesthesia, follow instructions on not eating or drinking anything before the test.

How the Test will Feel

During the biopsy, there is usually little or no discomfort. You may feel some pressure or tugging.

The anesthetic may burn or sting when injected (before the area becomes numb). After the anesthetic wears off, the area may be sore for about a week.

Why the Test is Performed

A muscle biopsy is done to find out why you have muscle weakness or your muscle enzyme lab tests are elevated and your provider suspects you have a muscle disease.

A muscle biopsy may be done to help identify or detect:

• Inflammatory diseases of muscle (such as polymyositis or dermatomyositis)

  Polymyositis or dermatomyositis

  Polymyositis and dermatomyositis are rare inflammatory diseases. (The condition is called dermatomyositis when it involves the skin. ) These disease...

  

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• Diseases of the connective tissue and blood vessels (such as polyarteritis nodosa)
• Infections that affect the muscles (such as trichinosis or toxoplasmosis)
• Inherited muscle disorders such as muscular dystrophy or congenital myopathy
• Metabolic defects of the muscle
• Effects of medicines, toxins, or electrolyte disorders

A muscle biopsy may also be done to tell the difference between nerve and muscle disorders.

A muscle that has recently been injured, such as by an electromyography (EMG) needle, or is affected by a pre-existing condition, such as nerve compression, should not be selected for a biopsy.

Electromyography

Electromyography (EMG) is a test that checks the health of the muscles and the nerves that control the muscles.

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An MRI may be done in advance to show the best site for the biopsy.

Normal Results

A normal result means the muscle is normal.

What Abnormal Results Mean

A muscle biopsy can help diagnose the following conditions:

• Loss of muscle mass (atrophy)

  Atrophy)

  Muscle atrophy is the wasting (thinning) or loss of muscle tissue.

  

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• Muscle disease that involves inflammation and a skin rash (dermatomyositis)
• Various muscular dystrophies (Duchenne muscular dystrophy and other conditions)
• Destruction of the muscle (myopathic changes)
• Tissue death of the muscle (necrosis)
• Disorders that involve inflammation of the blood vessels and affect muscles (necrotizing vasculitis)
• Traumatic muscle damage
• Paralyzed muscles
• Inflammatory muscle disease causing muscle weakness, swelling tenderness, and tissue damage (dermatomyositis or polymyositis)
• Nerve problems that affect the muscles

There are additional conditions under which the test may be performed.

Risks

The risks of this test are small, but may include:

• Bleeding
• Bruising
• Damage to the muscle tissue or other tissues in the area (very rare)
• Infection (a slight risk any time the skin is broken)

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