What is a nerve conduction velocity test (NCV) or nerve conduction study (NCS)?
A nerve conduction velocity test (NCV) – also called a nerve conduction study (NCS) – measures how quickly electrical impulses move through a nerve. NCV can determine nerve damage.
During the nerve conduction study test, your nerves are stimulated, and electrode patches are usually attached to your skin. Two electrodes are located on the skin over the nerve. One of the electrodes stimulates the nerve with a very light electrical pulse. Scored by the other pole. The resulting electrical activity is registered by another electrode. This is repeated for each nerve that is tested.
The velocity is then calculated by measuring the distance between the electrodes and the time taken for the electrical impulses to travel between the electrodes.
One of the related tests that may be performed is electromyography (EMG). This measures the electrical activity in your muscles. It is often performed at the same time as a nerve conduction study (NCV). Both tests help find the presence, location, and extent of diseases that damage nerves and muscles.
Do I need EMG or NCS?
It’s normal to feel pain or numbness in the muscle from time to time. Your wrist muscle might strain while lifting something heavy, for example.
However, for many people, wrist inflammation is caused by an injury to the nerve, not the affected muscle. When it is not clear why you have problems with your wrist, back, legs, or any other part of your body, one or both of these tests may be helpful.
Tests may be done for people who show the following symptoms that don’t go away:
- Pain or cramping
- Tingling or numbness
- Muscle weakness
Who gets a nerve conduction study test?
The NCV test can be used to diagnose a number of muscular and neuromuscular disorders, including:
- Guillain-Barré syndrome
- Carpal tunnel syndrome
- Charcot-Marie-Tooth disease (CMT)
- Hard drive disease
- Chronic inflammatory neuropathy and neuropathy
- Sciatic nerve problems
- Peripheral nerve injury
If your doctor suspects you have a pinched nerve, he or she may recommend an NCV test.
An EMG test is often done alongside the NCV test. An electromyogram test records the electrical signals moving through your muscles. This helps reveal the presence, location, and extent of any disease that may damage nerves and muscles.
Will I need to do anything to prepare for these nerve conduction study tests?
- Tell your healthcare provider if you have a pacemaker or cardiac defibrillator. Special steps should be taken before testing if you have one of these devices.
- Wear loose, comfortable clothing that allows easy access to the test area or can easily be taken off if you need to wear a hospital gown.
- Make sure your skin is clean. Do not use lotions, creams, or perfumes for a day or two before the test.
What happens during a nerve conduction study?
- You will sit or lie on a table or bed.
- Your provider will attach one or more electrodes to a specific nerve or nerves using duct tape or paste. The electrodes, called stimulation electrodes, deliver a mild electrical impulse.
- Your provider will connect different types of electrodes to the muscles or muscles that control those nerves. These electrodes will record the responses to electrical stimulation from the nerve.
- Your provider will send a small electrical pulse through the stimulating electrodes to stimulate the nerve to send a signal to the muscles.
- This may cause a slight tingling sensation.
- Your provider will record the time it takes your muscles to respond to the nerve signal.
- The speed of response is called the conduction velocity.
What happens after a nerve conduction study (NSC)/EMG?
After the nerve conduction study test, you will be permitted to wear your clothes and shoes. It should be noted that the final interpretation of the clinical meaning of the text rests with the physician who ordered the test. This is because they can compile the entire image.
For this reason, the neurologist who performs the test can only give you limited information about what the results mean, and may not even be able to provide any information about the next step or any potential treatments because they are unaware of all the other clinical information.
Side effects of an NCS/EMG
Rarely, there are any side effects from the NCS procedure. Although some discomfort (for some palpable ones) is felt during the test, there are often no complications afterwards. The doctor may avoid stimulation near the stump if you have a pacemaker or similar device.