Frequently Asked Questions: What is an EMG or NCS?

Electrodiagnostic studies include electromyography (EMG); nerve conduction studies (NCS); and evoked potentials (EP). Like imaging studies, these studies cannot confirm the presence or absence of pain. They are most useful in evaluating a patient when pain is present with an observed neurological deficit.

Electromyography (EMG) is the most commonly used test to assess the function of the nerve roots leaving the spine. The test is done by inserting tiny electrodes into the muscles of the arm or leg. By looking for abnormal electrical signals in the muscles, the EMG reveals nerve irritation, or pinching of the nerve, as it leaves the spinal canal.

Think of how you test the wiring on a lamp. If you place a working bulb into the lamp, and the bulb lights up, you assume that the wiring is okay. However, what if the bulb does not light up? You may safely assume that something is probably wrong with the wiring, like the lamp is unplugged, or a short circuit has occurred. By relating the muscles to the light bulb in the lamp, the EMG is able to determine the condition of the nerves that supply those muscles, like the wiring on the lamp. If the EMG machine finds that the muscles (the light bulb) are not working properly, the doctor may assume that the nerves (the wiring) must be irritated or pinched somewhere.

Learn more about EMG/NCS:


More Frequently Asked Questions:

What is degenerative disk disease?
What is sciatica?
What is a bulging/ruptured/herniated disk?
What is radiculopathy/nerve impingement?
What is spinal stenosis?
What is the difference between x-rays, MRI, and CT scan?
What is physical therapy?


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