Electromyography (EMG) and Nerve Conduction Velocity (NCV) Tests
Electrodiagnostic Testing for Muscle and Nerve Problems
Electromyography (EMG) and nerve conduction velocity (NCV) are electrodiagnostic tests performed to measure the electrical activity of muscles and nerves. These tests may be an important part of a spine patient’s work-up by their doctor. Some patients with a spine-related problem report unexplained symptoms, numbness and/or tingling sensations, muscle cramping, or weakness in an extremity (eg, one or both arms, legs).
Your doctor may refer you to a neurologist and/or physiatrist for an EMG and NCV. Both tests are often performed during the same appointment. An EMG and NCV may be performed to determine:
- Is the problem muscle- or nerve-related?
- Is there nerve damage?
- What is causing nerve damage?
- Are the damaged nerves responding to treatment? (If the patient is receiving treatment)
The neurologist and/or physiatrist will analyze the results of the test(s) and prepare a written report that is sent to the referring doctor.
Before EMG or NCV tell your doctors if:
- You take blood-thinning medication.
- You regularly take aspirin.
- Have a bleeding disorder.
Electromyography measures muscle response to nerve stimulation and evaluates electrical activity within selected muscle fibers. This test may help to differentiate between a muscle disorder and a nerve disorder, which can help your doctor to make an accurate diagnosis.
- What to Expect During EMG
A thin needle electrode is inserted through your skin into a specific muscle. As you relax and contract the muscle, the electrical impulses are recorded on an oscilloscope; a device that displays the electrical impulses in a wave-like pattern. Additionally, the doctor may listen to the results through a speaker.
Nerve conduction velocity measures the speed at which an electrical impulse travels along a nerve.
- What to Expect During NCV
Patch-like electrodes are applied to your skin in several places over the nerve to be tested. Low level electricity is dispensed through the electrodes to stimulate the nerve. The amount of electricity is similar to a shock from static electricity. The velocity at which the electrical signal flows through the nerve is measured and displayed on a screen.
Preparing for EMG or NCV
- Avoid skin lotion or cream on the areas to be tested.
- During the test, you may be instructed to sit and/or lay down.
Discomfort and Risks
- EMG: You may feel discomfort when the needle electrodes are inserted.
- NCV: You may feel startled when the electrical pulses are generated.
- After EMG: The muscle(s) tested may feel sore.
- After EMG: Minor bleeding or bruising where the needle electrodes were inserted.
- EMG Risk: Small risk of infection where the needle electrodes were inserted.
American Academy of Orthopaedic Surgeons. OrthoInfo. Electrodiagnostic Testing. http://orthoinfo.aaos.org/topic.cfm?topic=a00270. Accessed February 17, 2015.
The Foundation for Peripheral Neuropathy®. Electrodiagnostic Testing. https://www.foundationforpn.org/livingwithperipheralneuropathy/evaluation/electrodiagnostictesting/index.cfm. Accessed February 17, 2015.