What is a nerve conduction velocity test?

A nerve conduction velocity (NCV) test measures how fast an electrical impulse moves through your nerve. NCV can identify nerve damage. This test is also called a nerve conduction study.

During the test, your nerve is stimulated, often with electrode patches put on your skin. Two electrodes are placed on the skin over your nerve or over a muscle. One electrode stimulates your nerve with a very mild electrical impulse. The other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.

The speed is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.

A related test that may be done is electromyography (EMG). This measures the electrical activity in your muscles. It should usually be done during the same visit as an NCV. Both tests help find the presence, location, and extent of diseases that damage the nerves and muscles.

Why might I need a nerve conduction velocity test?

NCV is often used along with an EMG to tell the difference between a nerve disorder and a muscle disorder. NCV finds a problem with the nerve, whereas an EMG finds whether the muscle is working the right way in response to the nerve's stimulus.

Diseases or health problems that may be checked with NCV include:

• Guillain-Barré syndrome. A condition in which the body's immune system attacks part of the peripheral nervous system. The first symptoms may include weakness or a tingling sensation in the legs.

• Carpal tunnel syndrome. A health problem in which the median nerve, which runs from the forearm into the hand, becomes pressed or squeezed at the wrist by enlarged tendons or ligaments. This causes pain and numbness in the fingers.

• Charcot-Marie-Tooth disease. An inherited neurological condition that affects both the motor and sensory nerves. It causes weakness of the foot and lower leg muscles.

• Herniated disk disease. This health problem occurs when the fibrous cartilage that surrounds the disks of your vertebrae breaks down. The center of each disk, which contains a gelatinous substance, is forced outward. This places pressure on a spinal nerve. It causes pain and damage to the nerve.

• Nerve damage (neuropathy). This condition may occur from many health issues, such as diabetes, chemotherapy treatment, autoimmune disorders like chronic inflammatory demyelinating neuropathy, or alcoholism. Symptoms may include numbness or tingling in a single nerve or many nerves at the same time.

• Sciatic nerve problems. There are many causes of sciatic nerve problems. The most common is a bulging or ruptured spinal disk that presses against the roots of the nerve leading to the sciatic nerve. Pain, tingling, or numbness often result.

Nerve conduction studies may also be done to find the cause of symptoms, such as numbness, tingling, and ongoing pain.

Other health problems may cause your healthcare provider to recommend NCV.

What are the risks of NCV tests?

The voltage of the electrical pulses used during an NCV is considered very low. There are no known long-term side effects of NCV testing. The main side effect is short-term discomfort from the electrical stimulation.

Tell your healthcare provider if you have a cardiac defibrillator, pacemaker, or other implanted device. If you have one of these, precautions may need to be taken. Risks depend on your specific health problem. Be sure to discuss any concerns with your healthcare provider before the procedure.

Certain factors or conditions may interfere with the results of NCV tests. This includes damage to the spinal cord, severe pain before the test, and body temperature.

How do I get ready for an NCV test?

• Your healthcare provider will explain the procedure and you can ask questions.

• You may be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.

• Generally, you will not need to fast or get sedation before the procedure.

• Normal body temperature must be maintained before and during the procedure. Low body temperature slows nerve conduction. Let the examiner know if you feel cold.

• Tell your healthcare provider of all medicines (prescription and over the counter) and herbal supplements that you take. For some conditions, certain medicines may need to be adjusted.

• Dress in clothes that allow access to the area to be tested or that are easily removed.

• Stop using lotions or oils on your skin for a few days before your procedure.

• Based on your health problem, your healthcare provider may request other preparations. Let them know if you are taking blood-thinning medicines.

What happens during the NCV test?

An NCV procedure may be done on an outpatient basis, or as part of your stay in a hospital. Procedures may vary depending on your condition and your healthcare provider's practices.

The NCV and EMG is most often performed and interpreted by a neurologist or physiatrist. These are healthcare providers who have special training in NCS and EMG. A technologist may also do some parts of the test.

Generally, an NCV procedure follows this process:

1. You will be asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or other metal objects that may interfere with the procedure.

2. If you are asked to remove clothing, you will be given a gown to wear.

3. You will be asked to sit or lie down for the test.

4. A neurologist will locate the nerve(s) to be studied. The number of nerves tested depends on your case and what the provider is looking for.

5. A healthcare provider will attach a recording electrode to the skin over your nerve, using a special paste. They will then place a stimulating electrode away from the recording electrode, at a known distance.

6. A mild and brief electrical shock, given through the stimulating electrode, will stimulate your nerve.

7. You may experience minor discomfort for a few seconds.

8. The stimulation of the nerve and the response will be displayed on a monitor.

What happens after an NCV?

The paste used to attach the electrodes will be removed from your skin. Often, electromyography (EMG) is done at the same visit as NCV testing.

After the test, you may return to your previous activities, unless your healthcare provider advises you differently. Your healthcare provider may tell you to stay away from strenuous activities for the rest of the day.

Your healthcare provider may give you other directions after the procedure, depending on your situation.

Next steps

Before you agree to the test or procedure make sure you know:

• The name of the test or procedure

• The reason you are having the test or procedure

• What results to expect and what they mean

• The risks and benefits of the test or procedure

• What the possible side effects or complications are

• When and where you are to have the test or procedure

• Who will do the test or procedure and what that person’s qualifications are

• What would happen if you did not have the test or procedure

• Any alternative tests or procedures to think about

• When and how you will get the results

• Who to call after the test or procedure if you have questions or problems

• How much you will have to pay for the test or procedure