ENG measures the conduction of electrical signals along nerve pathways in the body. To perform ENG, small, patch-like sensors (electrodes) are applied to the skin at specific locations to measure the electrical activity of particular peripheral nervesthat is, nerves outside of the brain and spinal cord. By stimulating a nerve at one site and then recording the time it takes for the nerve impulse to travel to a second point, ENG is able to measure the velocity of nerve conduction. The detection of slowed conduction velocity with ENG indicates possible nerve disease or trauma.
ENG is typically performed in conjunction with electromyography, or EMGwhich measures the electrical activity of musclesin order to fully evaluate people who are experiencing weakness or paralysis. This combined procedure may be called electromyoneurography.
Purpose of the ENG
- To identify peripheral nerve damage or destruction and establish the precise location of the problem
- To differentiate peripheral nerve disease from muscular injury
Who Performs ENG
- A doctor or a technician
Special Concerns about ENG
- Because this test reflects the condition of the best surviving nerve fibers, normal values for ENG may be obtained if only a few fibers remain intact. For this reason, the test results may sometimes be normal despite the presence of extensive nerve damage.
Before the ENG
- Be sure to wear loose-fitting clothes on the day of the procedure so that it will be easy to expose the relevant nerves and muscles during the test.
- Do not use any hand cream or lotion to ensure that the test electrodes will adhere properly to your skin.
What You Experience
- A special electrical paste is applied to the skin overlying the particular muscle or muscle group that is served by the nerve being evaluated.
- Several electrodes are then placed on your skin—one that will stimulate a particular nerve with an electrical impulse, and the others to record the muscle response to this stimulus.
- A very mild electrical shock is delivered to the stimulating electrode, causing the muscles under the recording electrodes to contract. The shock is so small that most people cannot perceive it.
- The response of the muscle to this stimulus is recorded by the other electrodes.
- This process is repeated at other locations to test different nerves.
- This test takes approximately 15 minutes to perform.
Risks and Complications of ENG
- There are no significant risks or complications associated with this procedure.
After the ENG
- The examiner will remove the electrode gel from your skin.
- You are free to leave the testing facility and resume your normal activities.
- The nerve conduction velocity is calculated based on the distance between the stimulating and recording electrodes and the time elapsed between the nerve impulse and the resulting muscle contraction. The strength, or amplitude, of the nerve signal is also measured.
- Your doctor will evaluate the results for evidence of peripheral nerve disease. Since normal values vary in different nerves and from person to person, your symptoms and physical exam and the results of other tests will also be considered in order to make an accurate diagnosis.
- If a definitive diagnosis can be made, appropriate therapy will be initiated.
- Additional laboratory tests may be needed to identify the underlying cause of any nerve damagefor example, diabetes or hypothyroidism.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media