Electromyography (EMG) and Nerve Conduction Studies
Reviewed
Also called: EMG and Nerve Conduction Studies, Electrodiagnostic Study, EMG Test, Electromyogram, NCS, Nerve Conduction Velocity (NCV)
EMG and nerve conduction studies are tests that check how well your muscles and the nerves that control them are working. An EMG test looks at the electrical signals your muscles make when at rest and when used. A nerve conduction study measures how fast and how well your body's electrical signals move along your nerves. These tests can help find out if you have a health condition that has damaged your muscles or nerves or how they work together.
Specimen: Not applicable (this is a procedure, not a laboratory test).
Why this test may be ordered
- Muscle weakness
- Tingling or numbness in arms, legs, hands, feet, and/or face
- Muscle cramps, spasms, and/or twitching
- Paralysis of any muscles
Preparation and collection
Tell your provider if you have a pacemaker or cardiac defibrillator (special steps will be needed). Tell your provider if you take blood thinner medicines (you may need to watch for more bleeding from the needle). Wear loose, comfortable clothing. Make sure your skin is clean; do not use lotions, creams, or perfumes for a day or two before the test.
For EMG: a small needle electrode is inserted into the muscle. For NCS: electrodes are taped to the skin over a nerve and recording electrodes are attached to the muscles controlled by that nerve.
You may feel mild pain during an EMG test. You may have a tingly feeling, like mild static electricity, during a nerve conduction study. The muscles that were tested may be sore for a few days after the test. You may also have some bruises on your skin where the needles were placed.
Understanding results
Your provider will interpret the results of EMG and nerve conduction studies together with your symptoms, medical history, and other test results. The patterns below describe possible findings.
- Normal results: Normal muscle and nerve function. A healthy muscle should not give off electrical signals when at rest, and nerve signals travel at a normal speed and strength. Limitation: Results are not diagnostic on their own; your provider will consider your symptoms, medical history, and other test results. Next step: Your provider will determine if further evaluation is needed based on your overall clinical picture.
- Not normal results: Abnormal results can be a sign of many different conditions, such as carpal tunnel syndrome, herniated disk, Guillain-Barré syndrome, myasthenia gravis, muscular dystrophy, Charcot-Marie-Tooth disease, or amyotrophic lateral sclerosis (ALS). Limitation: Results are not diagnostic on their own; your provider will consider your symptoms, medical history, and other test results. Next step: Your provider will discuss the specific condition and appropriate follow-up based on your overall clinical picture.
- EMG may cause mild pain or discomfort when the needle electrode is inserted; if pain becomes very uncomfortable it may change test results.
- NCS may cause a mild tingling feeling (like mild static electricity) during the electrical pulse.
- The muscles tested may be sore for a few days after the test, and there may be some bruising where needles were placed.
- Results are not diagnostic on their own; your provider will consider your symptoms, medical history, and other test results.
What to do next
If your results are not normal, it can be a sign of many different conditions. Your provider will consider your symptoms, medical history, and the results of other tests to determine the cause. Talk to your provider about what your results mean.
- What symptoms led to this test being recommended?
- What do my results mean in combination with my medical history and other tests?
- Do I need any follow-up tests or appointments?
Evidence source
U.S. National Library of Medicine: Electromyography (EMG) and Nerve Conduction Studies