Explore This Procedure

About This Procedure

The EMG lab at Massachusetts General Hospital is staffed by board certified Electromyographers, physicians specializing in the diagnosis and testing of diseases of the peripheral nervous system. This laboratory is a tertiary referral lab for many of the neurologists, neurosurgeons, internists and orthopedists in New England.

What to Expect During Your EMG Test

Electrodiagnostic medicine is the study of diseases of nerves and muscles. Your doctor has recommended an EMG test to see if your muscles and nerves are working right. The results of the tests will help your doctor decide what is wrong and how it can be treated.

Types of Tests

Nerve Conduction studies
NCSs show how well the body’s electrical signals are traveling along a nerve. This is done by applying small electrical shocks to the nerve and recording how the nerve works. These shocks cause a quick, mild, tingling feeling. The doctor may test several nerves.

Needle EMG
For this part of the test, a small, thin needle is inserted into several muscles and the electrical activity of those muscles is recorded and analyzed. During the EMG test the doctor will be able to hear and see how your muscles and nerves are working by the way electrical signals appear on the EMG machine. There may be a small amount of discomfort when the needle is placed in.

Single Fiber EMG
This is a very sensitive and specialized test used to diagnose myasthenia gravis. It is a variation of the needle EMG exam. In a single fiber study, the doctor inserts a needle into one of your muscles and then samples the electrical potentials coming from your muscles while you maintain a low level of activation. This test takes about 20-30 minutes.

Autonomic Function Testing
This test includes four separate studies. The first three involve continuous heart rate and blood pressure responses to individual tasks. The heart rate and blood pressure are recorded with electrodes applied to your chest and wrist. The fourth part of the exam involves measuring how much sweat your body produces. Small recording devices are placed onto your forearm, leg and foot. These devices measure your sweat production in response to a very tiny electrical stimulus. There may be minimal discomfort with the sweat test; the first three tests are painless. The test takes about 90 minutes.

Muscle Biopsy
In this test, the doctor inserts a needle into one of your muscles and takes out a small portion of your muscle for analysis under a microscope. Anesthetic medication is first injected into your skin over the biopsy site to minimize discomfort. This test is especially useful for diagnosing myopathies (disorders of muscle). The procedure takes about 15 minutes and does not require stitches.

Frequently Asked Questions

Why am I being sent to the EMG lab for tests?
You are being sent to the electromyography (EMG) lab because you have numbness, tingling, pain, weakness, or muscle cramping. Some of the tests that the EMG doctor may use to diagnose your symptoms are nerve conduction studies (NCSs) and needle EMG. The EMG doctor will examine you to decide which tests to do.

How long will these tests take?
The tests usually take 20 to 90 minutes. You can do any of your normal activities like eating, driving, and exercising before the tests. There are no lasting side effects. You can also do your normal activities after the tests.

How should I prepare for the tests?
Tell the EMG doctor if you are taking aspirin, blood thinners (like Coumadin), have a pacemaker, or have hemophilia. Take a bath or shower to remove oil from your skin. Do not use body lotion on the day of the test. If you have myasthenia gravis, ask your doctor if you should take any medications before the test.

When will I know the test results?
The EMG doctor will discuss your test results with you or send them to your regular doctor. After the exam, check with the doctor who sent you to the lab for the next step in your care.

What kind of medical training do doctors who do EMGs have?
Doctors who do EMGs go to 4 years of medical school, and then have three or four more years of training in a residency program. Most work as a neurologists or physical medicine and rehabilitation doctors. All of our physicians have also completed an additional year of fellowship training in EMG and Neuromuscular Medicine and all have special board certification in this subspecialty area. Medical training helps the doctor decide which tests to perform based on your symptoms. It teaches doctors what can go wrong with the human body and how to tell the difference between these problems.

Who does the testing?
The American Association of Neuromuscular & Electrodiagnostic Medicine’s policy is that an appropriately trained doctor should do all needle EMG testing. A trained assistant or technologist under a doctor’s supervision can do nerve conduction studies.