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

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. When the needle is removed, a small piece of tissue remains in the needle. The tissue is sent to a laboratory for examination.

More than one needle insertion may be needed to get a large enough sample.

Open biopsy involves a small cut through the skin and into the muscle, so that a piece of muscle tissue can be removed from the affected area.

A muscle that has recently been injured, 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.

No fasting or other special preparation is usually necessary.

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 done to identify or detect:

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

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

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

A muscle biopsy can help diagnose the following conditions:

• Atrophy (loss of muscle mass)
• Necrosis (tissue death) of muscle
• Inflammation of the muscle
• Necrotizing vasculitis
• Myopathic changes (destruction of the muscle)
• Muscular dystrophy
• Traumatic muscle damage
• Duchenne's muscular dystrophy
• Polymyositis
• Dermatomyositis

Additional conditions under which the test may be performed include:

• 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 small, but may include:

• 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)