A muscle biopsy is a procedure involving the removal and examination of a piece of muscle tissue.

A muscle biopsy can usually be obtained while you are awake and the area being biopsied is numbed by local anesthesia. A needle biopsy may be adequate in children and adults with chronic conditions. In this procedure, a needle in 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 a pathologist for examination. More than one needle insertion may be needed to obtain a large enough specimen for testing and examination.

Open biopsy 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.

A muscle that has recently been traumatized, such as by an EMG needle, or that is affected by pre-existing condition, such as nerve compression, is not a good choice for a biopsy.

The muscle chosen for biopsy must be appropriate for the symptoms or suspected condition.

No fasting or other special preparation is usually necessary. You may be asked to wear loose clothing or a hospital gown so that the muscle chosen for biopsy is easily accessible.

You must sign an informed consent form.

For infants and children:

The preparation you can provide for this test depends on your child's age and experience. For specific information regarding how you can prepare your child, see the following topics:

• Infant test/procedure preparation (birth to 1 year)
• Toddler test/procedure preparation (1 to 3 years)
• Preschooler test/procedure preparation (3 to 6 years)
• Schoolage test/procedure preparation (6 to 12 years)
• Adolescent test/procedure preparation (12 to 18 years)

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

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.

A muscle biopsy may be performed for many reasons, including the following:

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

Normal muscle and related tissue anatomy. A microscopic examination with and without staining that shows no abnormalities is normal.

A muscle biopsy can reveal conditions such as the following:

• Atrophy (loss of muscle mass)
• Necrosis (tissue death) of muscle fibers
• Inflammation of the muscle
• Necrotizing vasculitis
• Myopathic changes (destruction of the muscle)
• Muscular dystrophy, indicated by antibody staining of the muscle biopsy specimen that can show deficient dystrophin
• Traumatic muscle damage
• Duchenne's muscular dystrophy
• Polymyositis
• Dermatomyositis

Additional conditions under which the test may be performed include the following:

• Becker's muscular dystrophy
• Charcot-Marie-Tooth disease (hereditary)
• Common peroneal nerve dysfunction
• Eosinophilic fasciitis
• Facioscapulohumeral muscular dystrophy (Landouzy-Dejerine)
• Familial periodic paralysis
• Friedreich's ataxia
• Polymyalgia rheumatica
• Senile cardiac amyloid
• Thyrotoxic periodic paralysis

The risks are minimal and may include the following:

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