Nerve Conduction and Electromyography
What is EMG Testing?
An electromyogram (EMG) is a test used to record the electrical activity of muscles. When muscles are active, they produce an electrical current. EMG Testing is used to detect abnormal electrical activity of muscles that can occur in many diseases and conditions.
Why is an EMG test done?
An EMG Test is often performed when patients suffer from
Sciatica pain, radicular pain, tingling, numbness, and
muscle weakness. The EMG test also helps to distinguish between muscle conditions in which the problems begin in the muscle, and muscle conditions in which muscle weaknesses occur due to nerve disorders. The EMG test can also be used to detect true weaknesses, as opposed to weaknesses from reduced use, pain, or lack of motivation. EMGs can also be used to isolate the level of nerve irritation or injury.
How is the EMG Test done?
The test has two parts:
Part I – Nerve Conduction Testing:
A nerve conduction velocity (NCV) test is often done at the same time as an EMG. In this test, the nerve is electrically stimulated with a stimulator device while an electrode detects the electrical impulse 'down-stream' from the site of stimulation. This is usually done by taping a surface electrode over the nerve at various locations. The resulting electrical activity after stimulation is recorded by the other electrode. The distance between the electrodes and the time it takes for electrical impulses to travel between electrodes is used to calculate the speed of impulse transmission (nerve conduction velocity). A decreased speed of transmission indicates nerve disease.
The NCV test can be used to detect true nerve disorders (such as Neuropathy) or conditions whereby muscles are affected by nerve injury (such as Carpal Tunnel Syndrome).
Part II – Needle Examination:
A fine needle is inserted through the skin into the muscle, and electrical activity is detected by this needle. The activity is displayed visually on an computer screen and may also be heard audibly with a speaker. After the doctor places the electrode, the patient is asked to contract the muscle (for example, to bend the elbow).
The presence, size, and shape of the wave form (called the action potential) produced on the computer screen provides information on the ability of the muscle to respond to nerve stimulation.
How to prepare for an EMG test?
Come wearing loose clothing like shorts and a T shirt with no skin lotion applied to arms and legs on the day of the test.
Does an EMG test hurt?
The test can be uncomfortable at times, but an experienced physician can take precautions to keep such discomfort to a minimum.