Electromyography (EMG) and nerve conduction velocity (NCV) Tests are two of the different tests done by neurologists in the diagnosis of certain neuromuscular diseases. What is it all about and how is it done?

An EMG is often used along with NCV to differentiate a muscle disorder from a nerve disorder. NCV detects a problem with the nerve, whereas EMG can detect diseases stemming from problems with the muscle itself.

What is EMG?

Electromyography (EMG) measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle. The test shows whether the weakness is caused by a neurological or muscle condition.

To perform the test, a needle electrode is inserted through the patient's skin into the muscle. To enable the electrical activity to be detected and displayed on an oscilloscope, the patient is asked to contract a muscle by bending an arm or leg depending on the location of the electrodes. Several electrodes may need to be placed at various locations to obtain an accurate testing. The wave displayed on the oscilloscope (monitor screen), gives the physician information about the ability of the muscle to respond to nervous stimulation. An audio-amplifier may also be used testing both the appearance and sound of the electrical potentials simultaneously. The activity can be heard sounding like crackling sounds on an old fashioned AM radio or like hail on a tin roof, when you contract your muscle.

The EMG is performed by a neurologist (a physician who specializes in brain and nerve disorders), although a technologist may also perform some portions of the test.

What is a nerve conduction velocity (NCV) test?

A related procedure that is often performed at the same time as EMG, is a nerve conduction velocity (NCV) test. NCV is a measurement of the speed of conduction of an electrical impulse through a nerve. NCV can determine nerve damage and destruction, and Both EMG and NCV procedures help to detect the presence, location, and extent of diseases that damage the nerves and muscles.

Patches called surface electrodes, similar to those used for ECG, are placed on the skin over the nerve at various locations. The surface electrodes may also be placed over the needles when an EMG test is performed at the same time. Each patch gives off a very mild electrical impulse, which stimulates the nerve. Electrical activity is recorded by the electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine the speed of the nerve signals.

Is it painful?

A sedative or pain reliever may be prescribed by the neurologist before the procedure. If a sedative is given before the procedure, you may need to have someone drive you home afterwards.

If the neurologist, or the assistant, does not apply warm compresses to the affected areas to ensure that the muscles and nerves are at normal body temperature, before the test begins, ask for it to be done. Personal experience with the test been performed to cold nerves and muscles resulted in an emotional and very painful 40 minutes during the test. On another occasion the test was done on properly heated muscles and nerves and largely reduced trauma and unnecessary pain.

Some discomfort, similar to the feeling of an injection or an acupuncture needle, may be felt when the needle electrodes are inserted into the muscle. Personal experience taught me that, as with any injection, the pain differ from person to person placing the needle into the skin. The muscle may feel sore for a few days and a bruise may appear at the needlestick site.

The impulse of the nerve conduction velocity (NCV) may feel like an electric shock. Depending on how strong the stimulus is, you will feel it to varying degrees, and it may be uncomfortable. You should feel no pain once the test is finished.

These tests may be used to evaluate many problems/disorders including, but not limited to the following:

- neuromuscular diseases, such as Charcot-Marie-Tooth (CMT), myasthenia gravis
- motor problems, such as involuntary muscle twitching
- nerve compression or injury, such as carpal tunnel syndrome
- nerve root injury, such as sciatica
- muscle degeneration, such as muscular dystrophy

Please Note:

The content provided in this article is for informational purposes only, and was not designed or intended to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your physician. Please consult your physician with any questions or concerns you may have regarding your condition.