A nerve in the body works somewhat like an electrical wire in your house. If you want to see if the wire is functioning properly, you need to make sure that electricity can run through it. If there are any problems along its length, you will know it by a failure of the electrical current to go through.
Similar to testing current flow in a wire, nerve conduction velocity test (NCV) is an electrical test, ordered by your doctor, used to detect abnormal nerve conditions. It is usually ordered to diagnose or evaluate a nerve injury in a person who has weakness or numbness in the arms or legs. It also helps to discover how severe the condition is and how a nerve is responding to injury or to treatment. In this test, electrical signals are sent down specific nerves of the arms or legs, where an electrode placed on the skin detects the electrical impulse ‘down stream’ from the first. The nerve is stimulated with a tiny electrical current at one point. A nerve stimulator placed over the nerve supplies the nerve with a very mild electrical impulse. This electrical activity is recorded by the recording skin electrode. When this happens, you will feel a tingling sensation that may or may not be uncomfortable. Between the brief shocks you will not feel discomfort. The distance between the skin electrodes and the time it takes for electrical impulses to travel between electrodes is used to calculate the speed of the nerve signal. A decreased speed suggests nerve disease. A healthy nerve will transmit the signal faster and stronger than a sick nerve.
Usually NCV testing takes less than 30 minutes depending on the number of nerves tested.
The small amount of current delivered to the nerve is always at a very safe level. Patients wearing pacemakers or other electrical devices need not worry since this current will rarely interfere with such devices.
The electrical stimulation may be mildly uncomfortable but this is usually very brief when testing is done by an experienced physician. Most of our patients comment that the test was far easier to complete than they were told or expected.
You may be given instructions about how to prepare for a nerve conduction velocity test. Generally keeping the area to be tested warm, dry and free of lotions provides the best result. Skin temperature should be warm if possible for the test, because low body temperatures slow nerve conduction and falsely change test results.
Normal results from a NCV test only mean that there is no evidence of measurable damage or disease in the nerve. This test does not measure pain. In a small number of cases, nerve disease may still exist despite normal results. This is because other healthy fibers in the same nerve may show a normal reaction time.
Any other questions or concerns can be answered when you are seen in the office or can be answered by our staff by phone before you test.
An EMG (electromyogram) may be ordered to see if you have a pinched nerve in the back or the neck. If you have tingling or numbness in your arms or legs, an EMG may also show if you have nerve pressure there. The EMG measures the electrical activity in muscles. Muscles normally receive constant electrical signals from healthy nerves.
During this test, the doctor uses acupuncture-like needles to record electrical sounds from the various muscles in the arm or leg. If a muscle does not receive normal signals from a sick nerve, it broadcasts abnormal noise signals through the needle to a sound amplifier to help the doctor identify if a muscle is not correctly working with the nerve attached to it.
The EMG is performed by a specialized physician, the Electromyographer, who has completed extensive training and certification in EMG/NCV testing, usually a Physiatrist (Specialist in Physical Medicine and Rehabilitation) or a Neurologist. In some offices, parts of the test (the nerve conductions) are performed by a nurse or technician. At Total Spine Specialists, your entire test will be completed by the physician. The quality of the results and the time required to finish is quite dependent on the skill and training of the physician administering the test. The physicians at Total Spine Specialists have completed thousands of EMG/NCV tests over many years and can accurately and rapidly complete your testing in the minimum amount of time and discomfort.
An EMG takes anywhere between 15 to 30 minutes, depending on how extensive a test is required.
Few preparations are needed on the day you have an EMG. You do not need to fast or eat any particular kinds of food before the test. You can drive yourself to and from the test, so you do not need to bring a friend or a relative along. You can count on resuming your regular activity after the test is completed.
With few exceptions, you may continue taking medication prescribed by your physician as ordered. However, if you are taking a blood thinner, you should mention this to the office only if you are having an EMG done. There are no medication precautions for the NCV test.
We recommend you take two Tylenol tablets after the test for discomfort. Because the test requires help by the patient for best results and is usually well tolerated, no sedation is given.
Although the physician performing the test has a general idea of what the findings are during the test, the full results are only arrived at after more calculations and measurements are performed after the end of the test. The results are therefore usually not ready until later that day, or the next day in complicated cases. Your results will be sent to the referring physician or other specialists in a detailed report.