Nerve conduction velocity study (NCV) measures basic parameters of the nerve function – strength and speed of how an electrical signal (action potential) spreads through the nerve. This data complements electromyography (EMG) in making the diagnosis.
Both nerves and muscles produce electrical signals called action potentials which are detected and measured during NCV. A nerve is actually a bundle of axons - long twigs of nerve cells conducting electrical signals from one end of the nerve to another. An NCV machine is able to detect and analyze these tiny electrical signals coming from active neurons.
In motor nerves, these electrical signals travel toward the muscle causing muscle contraction.
In sensory nerves, these electrical signals travel toward the spinal cord, bringing signals from skin and other tissues which we feel as different sensations like temperature, pain, pressure and others.
NCV and Axons
NCV measures different characteristics of action potentials traveling along the axons, and is invaluable in diagnosing diseases that primarily affect nerve function. NCV uses electrodes similar to those used in electrocardiograms placed on the skin over a nerve. A mild electrical shock delivered to the nerve causes action potential which is recorded by other electrodes as it travels through the nerve.
The speed of nerve conduction is influenced by a coating around axons, called myelin. Myelin insulates each axon and forces action potentials to "jump" quickly along the axon. Action potential travels slower when myelin is damaged. Healthy axons provide a strong action potential. If axons degenerate the action potential becomes weaker.
Different diseases preferentially either affect myelin sheathing or damage axons. This is why the type of nerve damage detected by NCV is so important in making the right diagnosis.
A Little Discomfort
Though some people may find the electric shocks of the NCV or the needle pricks of the EMG uncomfortable these methods do not leave any permanent damage and are quite tolerable. NCV and EMG have remained for decades the gold standard in evaluating nerve and muscle function. Considering that there are more than two hundred different diseases affecting nerves and muscles NCV and EMG are very important and valuable tools in gathering data on the type, distribution and severity of damage. This data is useful in making an accurate diagnosis and starting an appropriate treatment earlier. Patients usually understand that EMG is a valuable tool and that the benefit of precise diagnosis outweighs discomfort of the procedure.
Dr. Kaplan has great sympathy for your discomfort because he performed NCV and EMG tests on himself literally dozens of times adjusting the equipment or learning new techniques.
Please, ask the doctor all your questions about the NCV test before the beginning of the test.
Please tell the doctor if you have a pacemaker or any other implanted device or take coumadin.
These tests may be contraindicated to you.
Please leave your rings, bracelets and watches at home to avoid their loss.
Do not use skin lotion at all to prevent inacurate test results.