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

This procedure is usually done while you are awake. The 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. The tissue is sent to a laboratory for examination. 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.

No special preparation is usually needed.

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:

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

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

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

A normal result means there is normal muscle and related tissue anatomy. There are no abnormalities seen when the tissue sample is stained and examined under a microscope.

A muscle biopsy can help diagnose the following conditions:

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

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:

• 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)