Nerve Conduction Studies (NCS) and Electromyography (EMG) are common procedures performed in the Neurology clinic to help detect neuromuscular abnormalities, such as peripheral neuropathy, carpal tunnel syndrome, myopathy, myasthenia gravis, and others.
NCS is a measurement of the amount and speed of conduction of an electrical impulse traveling through a nerve. It is used to detect the presence of any nerve abnormalities, as well as to determine the location and extent of nerve damage.
EMG is a measurement of electrical activity within muscle. It is used to detect the presence of any primary muscle abnormalities, and it also provides secondary information related to the nerves controlling the muscles.
About the procedure (NCS)
Before the procedure:
- The doctor or electrodiagnostic technician will explain the procedure to you and offer you the opportunity to ask any questions you may have.
- Fasting and other preparations are not required before the test.
- Notify your doctor if you have a pacemaker, in-dwelling catheter (sometimes called a ‘port’), or if you are taking anti-coagulation medicines (Coumadin, Eliquis, Pradaxa, etc).
- Dress in clothes that permit access to the area to be tested or that are easily removed (T-shirts or tank-tops for arms, shorts for legs). If you are asked to remove clothing, you will be given a gown to wear.
- You may be asked to remove any clothing, jewelry, eyeglasses, etc that may interfere with the procedure.
- Do not apply lotions or oils on your skin on the day of the exam.
- Based on your medical condition, your doctor may request other specific information.
During the procedure:
NCS / EMG are performed by a neurologist (a doctor who specializes in brain and nerve disorders), although an electrodiagnostic technician may perform some portions of the NCS. The procedure typically takes 45-60 minutes to complete.
Usually, the NCS portion is performed first:
- You will be asked to sit or lie down for the test.
- The doctor or a electrodiagnostic technician will locate the nerve(s) to be studied.
- 3 recording electrodes will be attached to the skin over the nerve.
- The nerve will be stimulated by a mild and brief electrical shock given through the stimulator.
- You may experience minor discomfort for a few seconds.
- The stimulation of the nerve and the detected response will be displayed on the computer monitor as variable waveforms.
- The nerve is often stimulated several times to ensure the correct waveform (nerve response) is obtained.
The EMG procedure follows the NCS:
- The doctor will locate the muscle(s) to be studied.
- A recording electrode will be attached to the skin near the muscle.
- The skin will be cleansed with an alcohol swab. Next, a small, thin, sterile needle will be inserted into the muscle.
- You will be asked to relax the muscle, and the needle will be briefly moved to check different areas of the muscle.
- You may experience slight pain with the insertion of the needle, or with needle movements. If the pain is excessive, inform the doctor so that adjustments can be made to minimize the discomfort.
- You will then be asked to perform slight or full-strength contractions of the muscle being studied.
- The electrical activity from your working muscle will be measured and displayed on the computer screen, as well as an audio recording of the muscle, that sounds like hail on a tin roof when you contract your muscle.
After the procedure:
- After the test, you may return to all previous activities without limitation, unless your doctor advises you differently.
- Some muscle soreness may persist for 1-2 days following the procedure. Notify your doctor if you experience increasing pain, tenderness, swelling, or pus at the needle insertion sites. Your physician may give you additional or alternate instructions after the procedure, depending on your situation.