How does an NCV test work?

A nerve conduction velocity (NCV) test is used to assess nerve damage and dysfunction. Also known as a nerve conduction study, the procedure measures how quickly electrical signals move through your peripheral nerves.

Your peripheral nerves are located outside of your brain and along your spinal cord. These nerves help you control your muscles and experience the senses. Healthy nerves send electrical signals more quickly and with greater strength than damaged nerves.

The NVC test helps your doctor differentiate between an injury to the nerve fiber and an injury to the myelin sheath, the protective covering surrounding the nerve. It can also help your doctor tell the difference between a nerve disorder and a condition where a nerve injury has affected the muscles.

Making these distinctions is important for proper diagnosis and determining your course of treatment.

An NCV test can be used to diagnose a number of muscular and neuromuscular disorders, including:

If your doctor suspects you have a pinched nerve, they may recommend an NCV test.

An electromyography (EMG) test is often performed alongside an NCV test. An EMG test records the electrical signals moving through your muscles. This helps detect the presence, location, and extent of any disease that may damage the nerves and muscles.

When scheduling this test, your doctor will ask about conditions, medications, or behaviors that might affect the results. These include:

  • alcohol abuse
  • use of certain neurologic medications, such as muscle relaxants, opioids, or psychotropic medications
  • diabetes
  • hypothyroidism
  • systemic diseases

It’s also important for your doctor to know if you have a pacemaker. The electrodes used in the NCV test may affect the electronic impulses of your medical device.

Stop using any lotions or oils on your skin a few days before the test. These creams can prevent the electrode from being properly placed on the skin. Fasting usually isn’t necessary, but you may be asked to avoid caffeine beforehand.

Particulars of nerve conduction studies can vary, but they follow the same general process:

  1. You’ll be asked to remove any metal objects, such as jewelry, that could interfere with the procedure.
  2. You may need to remove some clothing and wear a gown.
  3. You will sit or lie down for the test.
  4. Your doctor will find the nerve to be tested.
  5. Your doctor will place two electrodes on your skin, one that stimulates the nerve and one that records the stimulation. They may use a jelly or some kind of paste to help the electrode stick to the skin.
  6. The nerve will be stimulated by a mild and brief electrical shock from the stimulating electrode. One common test, for example, stimulates nerves in the finger and records the stimulus with an electrode near the wrist.

The entire test may take 20 to 30 minutes. The sensation may be uncomfortable, but it typically isn’t painful.

Your doctor may want to perform the test in more than one location. In one study, researchers used the NCV test to examine damage to the ulnar nerve, which provides sensation to the hands and feet. Adding a third stimulation site to the two normally used increased the sensitivity of the test from 80 to 96 percent.

Your primary care doctor and the specialist who conducts the test can tell you when or if the test will need to be done again.

One advantage of an NCV test is that it’s considered an objective measurement of the health of a nerve, compared to subjective reports of pain or poor functioning. A nerve conduction velocity between 50 and 60 meters per second is generally considered in the normal range.

However, any result has to be examined along with other information. Your doctor will compare the results of your test against a standard, or norm, of conduction velocities. There’s no single standard. The results are affected by your age, what part of the body is tested, perhaps your gender, or even where you live.

A velocity outside of the norm suggests the nerve is damaged or diseased. However, it doesn’t indicate exactly what caused the damage. A large number of conditions can affect a nerve, such as:

  • carpal tunnel syndrome
  • traumatic median nerve damage
  • acute inflammatory polyneuropathy
  • chronic inflammatory polyneuropathy
  • diabetic neuropathy
  • drug-induced median nerve palsy
  • Guillain-Barré syndrome
  • Charcot-Marie-Tooth (CMT) disease
  • herniated disk disease
  • sciatic nerve problems
  • pinched nerves
  • peripheral nerve injury
  • damage from cancer drugs

Your diagnosis will depend on other information in your medical history and your physical symptoms.

There’s no single path to recovery from a damaged or diseased nerve. Treatment varies according to your specific condition, for example, and which nerve is affected.

Keep reading: Can diabetic neuropathy be reversed? »

Recovery is uncertain and often lengthy. Your age at the time of the injury plays an important factor. A nerve damaged at a very young age will react differently than if affected later in life. Nerve damage from a childhood injury may not become apparent until adolescence or later.

The length and severity of an injury makes a difference in your outlook. Sustained trauma may produce long-term or irreversible nerve damage, while the impact of a shorter exposure to the same injury may be reversed with rest.

Severe nerve damage may be treated with nerve grafts. Current research is also investigating the use of cultured cells to promote nerve regrowth.