Electromyography (EMG) and Nerve Conduction Studies (NCS)
If you have muscle pain or numbness, you may have one or both of these tests to determine how much of your nerves are being affected. These tests check how well your spinal cord, nerve roots, and the nerves and muscles that control your legs are functioning.
Electromyography (EMG) measures the electrical activity of muscles at rest and during contraction.
This test helps us find diseases that damage muscle tissue, nerves, or the junctions between nerve and muscle. These problems may include a herniated disc, amyotrophic lateral sclerosis (ALS), or myasthenia gravis (MG).
It can also help us find the cause of weakness, paralysis, or muscle twitching. Problems in a muscle, the nerves supplying a muscle, the spinal cord, or the area of the brain that controls a muscle can cause these symptoms. However, the EMG does not show brain or spinal cord diseases.
The test is performed by inserting a very thin needle electrode through the skin into the muscle. The electrode on the needle picks up the electrical activity given off by your muscles. This activity appears on a nearby monitor, and may be heard through a speaker. After placement of the electrodes, you may be asked to contract the muscle. For example, bending your arm. The electrical activity seen on the monitor provides information about your muscle’s ability to respond when the nerves to your muscles are stimulated.
Nerve Conduction Studies (NCS)
Nerve Conduction Studies measure how well and how fast the nerves can send electrical signals.
A Nerve Conduction Study is done to find damage to the peripheral nervous system, which includes all the nerves that lead away from the brain and spinal cord and the smaller nerves that branch out from those nerves. This test is often used to help us find nerve problems such as carpal tunnel syndrome or Guillain-Barré syndrome.
In this test, several flat metal disc electrodes are attached to your skin with tape. A shock-emitting electrode is placed directly over the nerve, and a recording electrode is placed over the muscles controlled by that nerve. Several quick electrical pulses are given to the nerve, and the time it takes for the muscle to contract in response to the electrical pulse is recorded. The speed of the response is called the conduction velocity.
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