How the Test is Performed

A muscle biopsy can usually be obtained under local anesthesia. A needle biopsy may be adequate in children and adults with chronic conditions. A needle inserted into the muscle. A small "plug" of tissue remains in the needle when it is removed from the muscle; this tissue is sent to the pathologist for examination. More than one needle insertion may be needed to obtain a large enough specimen.

Open biopsy may be needed, particularly when focal (localized) and/or patchy conditions are suspected. This involves a small incision through the skin and into the muscle, so that a sample of muscle tissue can be removed from the affected area.

The muscle chosen for biopsy sampling must be appropriate for the symptoms or suspected condition. The health care provider cannot use a muscle that has recently been traumatized by an EMG needle or that is affected by pre-existing disease such as nerve compression.

How to Prepare for the Test

No fasting or other special preparation is usually necessary. The muscle chosen for biopsy must be exposed (this may require loose clothing or a hospital gown). You must sign an informed consent form.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

• infant test or procedure preparation (birth to 1 year)
• toddler test or procedure preparation (1 to 3 years)
• preschooler test or procedure preparation (3 to 6 years)
• schoolage test or procedure preparation (6 to 12 years)
• adolescent test or procedure preparation (12 to 18 years)

How the Test will Feel

During the biopsy, there is usually minimal or no discomfort. Some pressure or "tugging" sensations may be noted. 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 1 week.

Why the Test is Performed

A muscle biopsy may be performed to:

• distinguish between neurogenic (nerve) and myopathic (primarily muscle) disorders
• identify specific muscular disorders such as muscular dystrophy or congenital myopathy
• identify metabolic defects of the muscle
• diagnose diseases of the connective tissue and blood vessels (such as polyarteritis nodosa)
• diagnose infections that affect the muscles (such as trichinosis or toxoplasmosis)

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