Electro-Diagnostic Testing (NCV/EMG)
Pain, weakness, tingling and numbness are all symptoms which may be caused by problems with nerves or muscles, and they can be physically disabling. Electrodiagnostic tests reveal how well your nerves and muscles are working and determine the existence, type and extent of any damage. Electrodiagnostic tests measure the electrical activity of muscles and nerves. By measuring the electrical activity, they are able to determine if there is nerve damage, the cause of the damage, and if the damaged nerves are responding to treatment.
Two common electrodiagnostic tests are:
- Electromyography (EMG)
- Nerve Conduction Velocity (NCV) Test
What is an EMG test?
An electromyogram (EMG) is a test that measures the electrical activity of a muscle. It detects any signs of blocking or slowing down of responses to nerve stimulation. The test provides information about the muscle itself and shows how well it receives stimulation from the nerve. A nerve conduction velocity (NCV) test is often done at the same time as an EMG. The purpose of an EMG test is to evaluate unexplained muscle weakness, twitching or paralysis, and to find the causes of numbness, tingling and pain. EMG testing can differentiate between true weakness vs. reduced use because of pain or lack of motivation. It can also determine whether a muscle disorder begins in the muscle itself or is caused by a nerve disorder.
What is an NCV test?
A nerve conduction velocity test (NCV), also called a nerve conduction study, measures how quickly electrical impulses move along a nerve. It is often done at the same time as an electromyogram (EMG), in order to exclude or detect muscle disorders. A healthy nerve conducts signals with greater speed and strength than a damaged nerve. The speed of nerve conduction is influenced by the myelin sheath—the insulating coating that surrounds the nerve. Most neuropathies are caused by damage to the nerve's axon rather than damage to the myelin sheath surrounding the nerve. The nerve conduction velocity test is used to distinguish between true nerve disorders (such as Charcot-Marie-Tooth disease) and conditions where muscles are affected by nerve injury (such as carpal tunnel syndrome).
EMG and NCV testing are ordered by a physician when a patient has signs or symptoms that indicate a nerve or muscle disorder. Symptoms may include numbness or tingling in the arms or legs, back or neck pain, certain types of limb pain, muscle pain, weakness or cramping, as well as burning sensation in the extremities. EMG and NCV testing are performed to help diagnose or rule out conditions such as carpal tunnel syndrome, radiculopathies, neuropathies, herniated discs, and nerve disfunction, among others.