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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Nerve conduction velocity

NCV

Last reviewed: May 28, 2013.

Nerve conduction velocity (NCV) is a test to see how fast electrical signals move through a nerve.

How the Test is Performed

Patches called surface electrodes are placed on the skin over nerves at various locations. Each patch gives off a very mild electrical impulse, which stimulates the nerve.

The nerve's resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to determine the speed of the nerve signals.

Electromyography (recording from needles placed into the muscles) is often done at the same time as this test.

How to Prepare for the Test

You must stay at a normal body temperature. Being too cold slows nerve conduction.

Tell your doctor if you have a cardiac defibrillator or pacemaker. Special steps will need to be taken before the test in you have one of these devices.

How the Test will Feel

The impulse may feel like an electric shock. You may feel some discomfort depending on how strong the impulse is. You should feel no pain once the test is finished.

Often, the nerve conduction test is followed by electromyography (EMG). In this test, needles are placed into a muscle and you are told to contract that muscle. This process can be uncomfortable during the test. You may have muscle soreness after the test at the site of the needles.

Why the Test is Performed

This test is used to diagnose nerve damage or destruction. The test may sometimes be used to evaluate diseases of nerve or muscle, including myopathy, Lambert-Eaton syndrome, or myasthenia gravis.

Normal Results

NCV is related to the diameter of the nerve and the degree of myelination (the presence of a myelin sheath on the axon) of the nerve. Newborn infants have values that are approximately half that of adults. Adult values are normally reached by age 3 or 4.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

Most often, abnormal results are due to nerve damage or destruction, including:

  • Axonopathy (damage to the long portion of the nerve cell)
  • Conduction block (the impulse is blocked somewhere along the nerve pathway)
  • Demyelination (damage and loss of the fatty insulation surrounding the nerve cell)

The nerve damage or destruction may be due to many different conditions, including:

  • Alcoholic neuropathy
  • Diabetic neuropathy
  • Nerve effects of uremia (from kidney failure)
  • Traumatic injury to a nerve
  • Guillain-Barré syndrome
  • Diphtheria
  • Carpal tunnel syndrome
  • Brachial plexopathy
  • Charcot-Marie-Tooth disease (hereditary)
  • Chronic inflammatory polyneuropathy
  • Common peroneal nerve dysfunction
  • Distal median nerve dysfunction
  • Femoral nerve dysfunction
  • Friedreich's ataxia
  • General paresis
  • Mononeuritis multiplex
  • Primary amyloidosis
  • Radial nerve dysfunction
  • Sciatic nerve dysfunction
  • Secondary systemic amyloidosis
  • Sensorimotor polyneuropathy
  • Tibial nerve dysfunction
  • Ulnar nerve dysfunction

Any peripheral neuropathy can cause abnormal results. Damage to the spinal cord and disk herniation (herniated nucleus pulposus) with nerve root compression can also cause abnormal results.

Considerations

An NCV test shows the condition of the best surviving nerve fibers, so in some cases the results may be normal even if there is nerve damage.

References

  1. Griggs RC, Jozefowicz RF, Aminoff MJ. Approach to the patient with neurologic disease. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 403.

Review Date: 5/28/2013.

Reviewed by: Luc Jasmin, MD, PhD, FRCS (C), FACS, Department of Neurosurgery at Cedars-Sinai Medical Center, Los Angeles CA; Department of Surgery at Los Robles Hospital, Thousand Oaks CA; Department of Surgery at Ashland Community Hospital, Ashland OR; Department of Surgery at Cheyenne Regional Medical Center, Cheyenne WY; Department of Anatomy at UCSF, San Francisco CA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.

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What works?

  • Enhanced glucose control for preventing and treating diabetic neuropathyEnhanced glucose control for preventing and treating diabetic neuropathy
    Diabetes is defined as high sugar levels in the blood. There are two forms of the disease. In type 1 diabetes, the body does not produce enough insulin. In type 2 diabetes, the body becomes less responsive to insulin. Regardless of the type of diabetes, many people develop a disabling neuropathy. Neuropathy is a condition that results in numbness, tingling, pain, or weakness that typically starts in the feet and progresses up the legs. The distribution is often described as a stocking glove pattern since the feet are affected first followed by the legs and fingers. The most common treatment for diabetes is control of blood sugar levels in an attempt to prevent the many complications, including neuropathy. This review identified 17 randomized studies that addressed whether more aggressive attempts to lower blood glucose levels prevent people from developing neuropathy. Seven of these studies were conducted in people with type 1 diabetes, eight in type 2 diabetes, and two in both types. However, only two studies in type 1 diabetes including 1228 participants and four studies in type 2 diabetes including 6669 participants investigated our primary outcome. In type 1 diabetes, there was a significant effect of more aggressive therapies in preventing neuropathy compared with standard treatment. In type 2 diabetes, more aggressive therapy was also beneficial in preventing symptoms and signs of clinical neuropathy, but the result was not statistically significant as measured by the primary method selected for this review. However, there was a significant positive effect on the amount of nerve damage measured with electrical nerve conduction tests and a special machine to measure the threshold of detection of vibration in both types of diabetes. Overall, the evidence indicates that more aggressive treatments of sugar levels delay the onset of neuropathy in both types of diabetes. No other treatments have proven effective to date. However, the beneficial effect has to be balanced against the significantly increased risk of dangerously low blood sugar levels that can occur in both types of diabetes and which can lead to brain injury amongst other issues.
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