Nerve Conduction Velocity
What is a nerve conduction velocity test?
A nerve conduction velocity (NCV) test — also called a nerve conduction study (NCS) — is a measurement of the speed at which an electrical impulse moves through your nerve. NCV can determine nerve damage.
During the test, your nerve is stimulated, usually with surface electrode patches attached to your skin. Two electrodes are placed on the skin over your nerve. One electrode stimulates your nerve with a very mild electrical impulse and the other electrode records it. The resulting electrical activity is recorded by another electrode. This is repeated for each nerve being tested.
The NCV (speed) is then calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes.
A related procedure that may be performed is an electromyography (EMG). This measures the electrical activity in your muscles and is often performed at the same time as an NCV. Both procedures help to detect 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 differentiate a nerve disorder from a muscle disorder. NCV detects a problem with the nerve, whereas an EMG detects whether the muscle is functioning properly in response to the nerve's stimulus.
Diseases or conditions that may be evaluated with NCV include, but are not limited to, the following:
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 condition 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 results in pain and numbness in the fingers.
Charcot-Marie-Tooth disease. A hereditary neurological condition that affects both the motor and sensory nerves. One characteristic is weakness of the foot and lower leg muscles.
Herniated disk disease. This condition 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 and causes pain and damage to the nerve.
Chronic inflammatory polyneuropathy and neuropathy. These are conditions resulting from diabetes or alcoholism. Symptoms may include numbness or tingling sensations 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 performed to identify the cause of symptoms, such as numbness, tingling, and continuous pain.
Other conditions may prompt 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 may be risks depending on your specific medical condition. 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, such as damage to the spinal cord, severe pain before the test, and body temperature.
Tell your healthcare provider if you have a cardiac defibrillator or pacemaker, as precautions may need to be taken.
How do I get ready for an NCV test?
- Your healthcare provider will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
- You will 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, no fasting or sedation is required before the procedure.
- Normal body temperature must be maintained before and during the procedure, as low body temperature slows nerve conduction.
- Notify your healthcare provider of all medications (prescription and over-the-counter) and herbal supplements that you are taking.
- Dress in clothes that permit 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 medical condition, your healthcare provider may request other specific preparation.
What happens during the NCV test?
An NCV procedure may be performed on an outpatient basis, or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.
The NCV is performed by a neurologist (a doctor who specializes in brain and nerve disorders), although a technologist may also perform some portions of the test.
Generally, an NCV procedure follows this process:
- You will be asked to remove any clothing, jewelry, hairpins, eyeglasses, hearing aids, or other metal objects that may interfere with the procedure.
- If you are asked to remove clothing, you will be given a gown to wear.
- You will be asked to sit or lie down for the test.
- A neurologist will locate the nerve(s) to be studied.
- A healthcare provider will attach a recording electrode to the skin over your nerve, using a special paste. He or she will then place a stimulating electrode away from the recording electrode, at a known distance.
- A mild and brief electrical shock, given through the stimulating electrode, will stimulate your nerve.
- You may experience minor discomfort for a few seconds.
- The stimulation of the nerve and the detected response will be displayed on an oscilloscope (a monitor that displays electrical activity in the form of waves).
What happens after an NCV?
The paste used to attach the electrodes will be removed from your skin.
After the test, you may return to your previous activities, unless your healthcare provider advises you differently. Your healthcare provider may instruct you to avoid strenuous activities for the rest of the day.
Your healthcare provider may give you additional or alternate instructions after the procedure, depending on your particular situation.
Before you agree to the test or the procedure make sure you know:
- The name of the test or procedure
- The reason you are having the test or procedure
- The risks and benefits of the test or procedure
- When and where you are to have the test or procedure and who will do it
- When and how will you get the results
- How much will you have to pay for the test or procedure