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Electromyogram (EMG) and Nerve Conduction Studies

Risks

An EMG is very safe. You may get some small bruises or swelling at some of the needle sites. The needles are sterile, so there is very little chance of getting an infection.

There is no chance of problems with nerve conduction studies. Nothing is put into your skin, so there is no chance of infection. The voltage of electrical pulses is not high enough to cause an injury.

Results

Your doctor may be able to tell you about some of the results of your nerve studies right after the tests. A full report may take 2 to 3 days.

Electromyogram (EMG) and nerve conduction studies

Normal:

The EMG recording shows no electrical activity when the muscle is at rest. There is a smooth, wavy line on the recording with each muscle contraction.

The nerve conduction studies show that the nerves send electrical impulses to the muscles or along the sensory nerves at normal speeds, or conduction velocities. Sensory nerves allow the brain to feel pain, touch, temperature, and vibration. Different nerves have different normal conduction velocities. Nerve conduction velocities generally get slower as a person gets older.

Abnormal:

Electrical activity in a muscle at rest shows that there may be a problem with the nerve supply to the muscle. Abnormal wave lines when a muscle contracts may mean a muscle or nerve problem, such as a herniated disc, amyotrophic lateral sclerosis (ALS), or inflammation.

In nerve conduction studies, the speed of nerve impulses is slower than what is normal for that nerve. Slower speeds may be caused by injury to a nerve or group of nerves. Nerve conduction velocities generally get slower as a person gets older.

The results from EMG and nerve conduction studies are used along with your medical history, symptoms, physical and neurological exams, and the results of other tests to help your doctor find out what the problem is or see how a disease is changing.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Taking medicines, such as muscle relaxants and anticholinergics.
  • Having bleeding, swelling, or too much fat under the skin at the site of the nerves or muscles being tested.
  • Not being able to do what is asked during the test.

What To Think About

  • The levels of some enzymes in the blood, such as aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and creatine phosphokinase (CPK), may rise when muscle tissue is damaged. An electromyogram can cause higher levels of these enzymes for up to 10 days after the EMG, so blood tests for these enzymes should not be done for 5 to 10 days after an EMG.
  • Special types of electromyograms (EMG) may also be done. For example:
    • Single-fiber EMG is a special type of EMG test. For this test, very small needles are inserted into a muscle to see how a single muscle fiber contracts. It is a useful test for myasthenia gravis, a disease that affects the nerve-muscle (neuromuscular) junctions.
    • Repetitive nerve stimulation is a useful test for myasthenia gravis and Lambert-Eaton syndrome. In this test, small, repeated shocks are given to measure how the muscle reacts to repeated nerve stimulation.
    • External sphincter electromyogram measures the electrical activity of the external urinary sphincter to help find urination problems. The urinary sphincter is a ring-shaped band of muscles around the urethra that helps control urination. The electrical activity can be measured by skin electrodes, by needle electrodes inserted through the skin, or by electrodes in an anal plug.

WebMD Medical Reference from Healthwise

Last Updated: November 30, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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