EMG (electromyogram)/NCS (nerve conduction study)

Description:

• EMG (electromyogram) is used to measure the electrical activity produced by muscle fibers.  The test is usually performed along with a NCS (nerve conduction study) which looks at the quality and speed of nerve signals as they travel to the muscles.

Indications:

• To evaluate unexplained muscle weakness, fatigue (tiredness), paralysis, or twitching.
• To localize nerve compression or injury in the spine.
• To diagnose peripheral nerve compression or injury, such as in carpal tunnel syndrome.
• To evaluate numbness or tingling in the extremities.
• To differentiate primary muscle conditions from muscle weakness caused by neurologic disorders.
• To help diagnose abnormalities in connections between the nerves and muscles.

What to expect:

            Prior to the test

• Avoid using any skin creams or lotions the day of the test.
• If you have a bleeding disorder or are taking medications that thin your blood (such as warfarin, aspirin, or clopidogrel), notify your doctor.
• Notify your doctor if you have a pacemaker.

Description of the test

• An EMG/NCS is completed in a hospital, clinic, or doctor’s office.
• The nerve conduction study portion of the test is completed first:
• Small metal patches (electrodes) will be taped to your skin over nerves at various locations.
• Then, a mild shock will be given off to stimulate the nerve. 
• The time it takes for the electrical impulse to travel from the stimulated nerve to the surrounding electrodes is recorded, along with the quality of the nerve’s overall electrical activity.
• This testing is typically done on several nerves and at different sites along a particular nerve.
• The electromyogram portion of the test is completed following the nerve conduction study.
• The EMG doctor will insert an electrode with a very thin needle into the muscle being tested to record its action potential (ability to respond when the nerves are stimulated).
• Several electrodes may be placed at various locations depending on your symptoms and size of the muscle.
• There will be no shocks given off during this study.
• During the test, you will hear a crackling speaker sound.  This is the electrical activity given off by your muscles.
• Periodically, you may be asked to contract or relax the muscle being tested.

After the test

• If you are having the test completed in a clinic or doctor’s office, you will be sent home afterwards without any activity restrictions.
• For a day or two after the test, your muscles may feel tender or you may notice small bruises or swelling around the electrode sites.

How long will it take?

• An electromyogram takes approximately 30 to 60 minutes.
• A nerve conduction study may take anywhere from 15 minutes to 1 hour depending on the number of nerves tested.
• The entire EMG/NCS testing generally takes about 1 to 1 ½ hours.

Will it hurt?

• The shocks given off during the nerve conduction study will produce a brief tingling or shock and a twitching of the muscle.
• The insertion of the needle electrodes during the EMG portion may be uncomfortable, but the pain is usually limited and resolves once the needle is removed.
• After the test, your muscles may feel bruised for 1 to 2 days.

Results:

• Immediately after the test, your doctor may be able to give you some information about the findings, but a full report usually takes 2 to 3 days.

Information from the National Institutes of Health, April 2010

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