Electromyogram

Electromyogram (often abbreviated as EMG) is a diagnostic procedure that evaluates the health condition of muscles and the nerve cells that control them (motor neurons). Motor neurons transmit electrical signals that cause muscles to contract. An EMG translates these signals into graphs, sounds or numerical values that a specialist interprets.

An EMG uses tiny devices called electrodes to transmit or detect electrical signals. During a needle EMG, a needle electrode inserted directly into a muscle records the electrical activity in that muscle. A nerve conduction study, another part of an EMG, uses electrode stickers applied to the skin (surface electrodes) to measure the speed and strength of signals traveling between two or more points.

Indications

EMG results can reveal nerve dysfunction, muscle dysfunction or problems with nerve-to-muscle signal transmission. EMG is often used to diagnose or rule out many conditions such as:

• Amyotrophic lateral sclerosis (ALS)
• Carpal tunnel syndrome
• Herniated disk disease
• Myasthenia gravis
• Peripheral neuropathy
• Polymyositis
• Muscular dystrophy

Procedure

The procedure for an EMG test can vary, but it generally involves the following steps:

• The patient is asked to lie down on an examination table.
• The skin is cleaned where the electrodes will be placed.
• A small needle (electrode) is inserted into the muscle to be tested.
• The patient is asked to contract the muscle (for example, by bending the arm).
• The electrical activity detected by the electrode is processed by a machine which produces an output (a graph, a sound, a numerical value) that is interpreted by a specialist.

Risks

While EMG is a relatively safe procedure, it may cause temporary discomfort and bruising. Serious side effects are rare.

See Also

• Nervous system
• Neurology
• Neurological disorders

References

• Mayo Clinic - EMG

Electromyogram Resources
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