EMG (electromyogram)
An EMG is used to measure the electrical activity produced by muscle fibers. The test is usually performed along with a NCS (nerve conduction study) which looks at the quality and speed of nerve signals as they travel to the muscles. This diagnostic test is done outside our clinic and our neurosurgeons utilize the results to assist in their diagnosis and identity the best treatment for your individual condition.
Used to :
- evaluate unexplained muscle weakness, fatigue (tiredness), paralysis, or twitching.
- localize nerve compression or injury in the spine.
- diagnose peripheral nerve compression or injury, such as in carpal tunnel syndrome.
- evaluate numbness or tingling in the extremities.
- differentiate primary muscle conditions from muscle weakness caused by neurologic disorders.
- help diagnose abnormalities in connections between the nerves and muscles.
What to expect:
Prior to the test
- Avoid using any skin creams or lotions the day of the test.
- If you have a bleeding disorder or are taking medications that thin your blood (such as warfarin, aspirin, or clopidogrel), notify your doctor.
- Notify your doctor if you have a pacemaker.
Description of the test
- The nerve conduction study portion of the test is completed first:
- Small metal patches (electrodes) will be taped to your skin over nerves at various locations.
- Then, a mild shock will be given off to stimulate the nerve.
- The time it takes for the electrical impulse to travel from the stimulated nerve to the surrounding electrodes is recorded, along with the quality of the nerve’s overall electrical activity.
- This testing is typically done on several nerves and at different sites along a particular nerve.
- The electromyogram portion of the test is completed following the nerve conduction study.
- The EMG doctor will insert an electrode with a very thin needle into the muscle being tested to record its action potential (ability to respond when the nerves are stimulated).
- Several electrodes may be placed at various locations depending on your symptoms and size of the muscle.
- There will be no shocks given off during this study.
- During the test, you will hear a crackling speaker sound. This is the electrical activity given off by your muscles.
- Periodically, you may be asked to contract or relax the muscle being tested.
After the test
- You will be sent home afterwards without any activity restrictions.
- For a day or two after the test, your muscles may feel tender or you may notice small bruises or swelling around the electrode sites.
How long will it take?
- An electromyogram takes approximately 30 to 60 minutes.
- A nerve conduction study may take anywhere from 15 minutes to 1 hour depending on the number of nerves tested.
- The entire EMG/NCS testing generally takes about 1 to 1 ½ hours.
Will it hurt?
- The shocks given off during the nerve conduction study will produce a brief tingling or shock and a twitching of the muscle.
- The insertion of the needle electrodes during the EMG portion may be uncomfortable, but the pain is usually limited and resolves once the needle is removed.
- After the test, your muscles may feel bruised for 1 to 2 days.
Results:
- Your neurosurgeon will be sent a full report.
Information from the National Institutes of Health, April 2010
