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What Is the Difference Between EMG and NCV?

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  • Written By: Jillian O Keeffe
  • Edited By: Shereen Skola
  • Last Modified Date: 06 July 2014
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EMG and NCV are both diagnostic tests that test electrical impulses in the body. Typically, a doctor performs them both together. Most often, the EMG involves needles and the NCV does not. EMG tests the health of the muscles and related nerves whereas NCV looks for problems only with the nerves.

Electromyography is the technical name of the EMG test. In healthy people, electrical impulses control the actions of muscles. NCV, on the other hand, stands for nerve conduction velocity. This test checks that the nerves can respond to stimuli properly.

The EMG and NCV procedures share some similarities. Both require the doctor to place electrodes in the area of the body being tested. Often, in EMG testing, however, the electrode is a needle, and the doctor needs to insert this directly into the muscle through the skin.

An NCV test, on the other hand, only requires a doctor to place patches that produce electrical impulses on the skin. Some EMG tests may use skin patches instead of needles. Electrodes, whether in the form of needles or patches, produce a small electrical impulse that acts on the muscles or the nerves during EMG and NCV tests.

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Usually, electrical activity in healthy people is not present at a high level during an EMG when the patient has relaxed muscles. When medical problems exist, such as inflammation or damage to the nerves that normally produce electrical stimuli for the muscles, then abnormal levels of electrical activity can show up on the EMG machine readout. Guillain-Barre Syndrome, myasthenia gravis, and carpal tunnel syndrome are just some of the conditions that the EMG analysis can help to identify.

NCV testing works in a different way to EMG testing, as the doctor does not look for the presence of abnormal impulses, but rather for the speed with which the electrode impulse moves through the nerve. For this reason, the NCV test always requires an electrode that produces an impulse, and another electrode at the opposite end of the nerve that detects the impulse. Slow impulses indicate nerve damage. NCV test results can form part of a diagnosis for many conditions that affect the nerves of the body, such as amyloidoisis, diptheria and trauma.

Doctors typically perform both the EMG and NCV tests together. The reason for this is that normal NCV tests can rule out issues with the nerves as a cause of muscle problems. The two tests can also help a doctor assess the extent of the damage that diseases have caused to patients.

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