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What is a Nerve Conduction Velocity (NCV) test? 
An NCV test is performed to determine the speed of impulses travelling through your nerves. It helps to look for and to understand the extent of nerve damage.

Nerves are long fibres that run throughout your body and carry information from the brain or spinal cord to body tissues. For the appropriate functioning of the body, it is essential that these nerves remain intact and carry information correctly. Nerve damage can change the speed of conduction of information. Certain disorders also disrupt the function of these nerves and thus affect the speed of conduction.
As nerves carry electrical information, the speed is calculated by placing electrodes on the skin. One electrode is used to stimulate the nerve, and the other is used to check the conduction. The test is usually safe and does not cause much discomfort. It is generally done before or after an electromyography test.

  1. Why is an NCV test performed?
  2. How do you prepare for an NCV test?
  3. How is an NCV test performed?
  4. What do NCV test results indicate?

An NCV test is recommended to patients who present with the following conditions/symptoms:

  • Tingling sensation or weakness in legs
  • Weakness in muscles of the lower part of the leg and foot
  • Pain or numbness in fingers
  • Radiating pain, numbness or tingling sensation from buttocks to lower legs
  • Radiating pain, numbness or tingling sensation from shoulders or neck to arms
  • Weakness, pain, tingling sensation or numbness in any other area of the body
  • Autoimmune diseases that could affect the nervous system

Also, your doctor may perform this test to see the side effects of any other condition in your body or monitor an ongoing treatment such as chemotherapy.

Extensive preparations are not needed for this test. Inform your doctor if you have any medical devices implanted in your body such as a pacemaker. Also, your doctor should know about any medicines, such as blood thinners, or any medical supplements if you are taking any. No lotion or moisturiser should be applied on the skin for 2-3 days before the test. Wear comfortable clothing for the test to ensure easy access to the testing area.

This procedure is performed by a neurologist or a technician. The steps mentioned below are usually followed:

  • You'll have to remove any metal objects, such as jewellery, glasses, hearing aids or hairpins before going for this test
  • A hospital gown is usually worn for the test, though it may be performed in regular clothes
  • Next, you'll be asked to lie down, and a neurologist will locate the nerve that needs to be checked
  • He/she will then stick electrodes on your skin at the area of the test. One electrode provides stimulation, and the other records the conduction
  • The recording electrode is placed at a specific distance from the stimulating one so the conduction speed can be calculated

Stimulation applied by the electrode might feel like a little stinging sensation or a mild shock, but this sensation will go away when the test is completed.

The responses from the recording electrode are seen on a screen, and the results are reported accordingly.
Normal body temperature should be maintained during the test, as a change in temperature may interfere with results.

Normal results: Results of an NCV test are generally given as metres/second (m/s). There are distinct values for nerves depending on the area of the body. Normal values for motor nerves of some of the common sites in adults are given in the table below. Values for newborns and children up to 3-4 years of age are about one-half compared to adults. 

 

Area of the body

Nerve

Conduction velocity

Forearm

Median nerve

More than 48 m/s

 

Ulnar nerve

More than 48 m/s

 

Common peroneal nerve

More than 40 m/s

Wrist

Median nerve

Less than 4.1 m/s

 

Ulnar nerve

Less than 3.8 m/s

 

Radial nerve

Less than 5 m/s

Values for motor nerves in legs are usually greater than 40 m/s, and values for sensory nerves all over the body are 10 m/s faster than motor nerves. Normal values may vary greatly from one laboratory to another. Speak with the doctor for a correct interpretation.

Abnormal results: NCV test results are considered abnormal if the values differ from the normal range. Abnormal results usually indicate nerve damage which may be due to the breakdown of fatty insulation (demyelination) over them or due to loss of one of the ends (axonal loss). The following table will illustrate a few examples of abnormal values.

Condition

Area of the body

Conduction velocity

Demyelination

Arms

Less than 40 m/s

 

Legs

Less than 30 m/s

Axonal loss

Arms

40-50 m/s

 

Legs

30-40 m/s

Your doctor will explain the results in detail depending on the underlying condition and how it affects the results. Different disorders that may be associated with abnormal values are as follows:

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. University of Rochester Medical Center. [Internet]. Rochester (NY): University of Rochester Medical Center; Nerve Conduction Velocity
  2. Gerard J. Tortora, Bryan Derrickson. [Iink] 14th ed. U.S: Wiley Publication; 2014. Chapter 28, Page no. 400-405
  3. American Association of Neurological Surgeons. [Internet] United States; Herniated Disc
  4. Griggs RC, Józefowicz RF, Aminoff MJ. [Internet] 25th Edition Philadelphia, PA: Elsevier Saunders; 2016: chap 396.
  5. Pennstate Hershey. [Internet] Milton S Hershey Medical Center, U.S. Nerve conduction velocity
  6. Johns Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; Nerve Conduction Velocity (NCV)
  7. Provan D. Oxford Handbook of Clinical and Laboratory Investigation 4th ed. United Kingdom: Oxford University Press; 2018. Chapter 9, Page no: 606-609, ISBN-13: 9780199233717