What is an EMG test?

Your doctor has just ordered a test called an EMG. EMG stands for Electromyogram which loosely translated means electrical testing of muscles but in fact has come to mean electrical testing of nerves and muscles. The EMG is performed by a specialist or specially trained MD, the Electromyographer, who is usually a Neurologist. Parts of the test (the nerve conductions) may be performed by a specially trained technician. It is an in-office procedure and does not require hospitalization. On average, an EMG takes anywhere between 30 minutes and 2 hours, depending on how extensive a testing your doctor orders on you. It can be done at any time during the day and, with few exceptions, does not require any special preparation.

Sometimes EMGs are thought to be a treatment of some sort, or a type of acupuncture. This is not true; an EMG is only a test, much like an EKG or an X-ray are tests and not treatments.

What are some problems for which EMGs are ordered?

EMGs are usually ordered when patients are having problems with their muscles or nerves. They test the nerves and muscles of the body’s extremities, looking for a problem in either one of these areas. An EMG may be ordered to see if you have a pinched nerve in the back or the neck. If you have tingling or numbness in your arms or legs, an EMG may show if you have a nerve entrapment somewhere or a nerve injury. Weakness of the muscles or “fatigue” (tiredness) may be indicative of nerve or muscle disease and require an EMG. There are many other medical problems that might suggest the need for an EMG. If you have any doubts as to why you need this test, ask your doctor.

What happens during an EMG?

During this test, you will be lying on an examination table, next to an EMG machine (which looks like a desktop or laptop computer). The test consists of two parts, though at times one may be done without the other.

Nerve Conduction Studies

The first part is called Nerve Conduction Studies. In this part some brief electrical shocks are delivered to your arm or leg in an effort to determine how fast or slowly your nerves are conducting the electrical current and therefore in what state of health or disease they may be. You see, a nerve works something like an electrical wire. If you want to see if the wire is functioning properly, the easiest thing to do is to run electricity through it. If there are any problems along its length, you will know it by a failure of the current to go through.

To do this, the doctor will attach small recording electrodes to the surface of one part of your limb, and will touch your skin at another point with a pair of electrodes delivering the shock. When this happens, you will feel a tingling sensation that may or may not be painful. Between the brief shocks you will not feel pain. As there are several nerves in each extremity which need to be tested, the procedure is repeated 3 or 4 times or more per extremity studied.

The amount of current delivered is always kept at a safe level. Patients wearing pacemakers or other electrical devices need not worry since this current will rarely interfere with such devices. During the nerve conduction study, the doctor or the technician performing the study will occasionally be pausing to make calculations and measurements.

Needle Examination

The second part of the test is called Needle Examination and as the name implies, involves some needle sticking. The needles used are thin, fine and about one and a quarter inches long. This part tests the muscle to see if there has been any damage to it as a result of the nerve problem or if the disease involves the muscle itself rather than the nerve.

Usually 5 to 6 muscles are sampled in one extremity, but occasionally, if you have problems in more than one area, additional muscles may need to be studied. The needle is usually inserted in the relaxed muscle and moved inside gently in order to record the muscle activity. When this is done, you will be able to hear the sound of the muscle activity amplified by the EMG machine; it will sound something like radio static.

The painful part of this section is when the needle is first inserted through the skin since all of the pain receptors are located in this area. Once inside the muscle, the sensation is usually perceived as discomfort or pressure rather than pain. During the needle exam, no electrical shocks are delivered. Also, since the needle probe is used here only as a recording device, no injections are given through the needle into the muscle. On the average, a muscle can be sampled in 2 to 5 minutes though this may vary with the type of problem being investigated.

How long does an EMG take?

The nerve conduction part of the test usually takes longer than the needle exam because one needs to make calculations and measurements during it. The needle exam is usually a faster procedure and also will not require all the extremities to be studied. On the average, one extremity takes from 20 to 45 minutes to test while two extremities take 30 minutes to an hour. An EMG of all four extremities can take up to 2 hours.

Does an EMG hurt?

There are some aspects of the EMG that might cause some discomfort, particularly the electrical shocks and the needle sticks. However, patients differ in how they perceive pain. Fortunately, the discomfort is limited to the time that the EMG is performed.

Should I take aspirin before an EMG?

There is no need to take aspirin before this test. There is some minor bleeding after the needle examination but it is minimal and can be controlled. So taking aspirin, or stopping it, should not have any effect on the study. If you are taking anticoagulants (blood thinners), check with your doctor.

What will be the results?

The EMG will reveal facts about your nerves and muscles. Most EMGs will show whether a nerve or nerve root problem (a pinched nerve) exists and give the doctor an idea about how serious the problem might be and how long you might have had it. EMGs rarely give an exact diagnosis; they just tell the doctor what type of problem exists. Many different diseases will yield similar results on the EMG, so correlating this information with the clinical exam and history is very important.

What happens after the test?

Unless you have been given certain medications, such as narcotics, you should be perfectly capable of driving yourself back home from the doctor’s office. No special precautions are necessary after the test. You can go back to work, exercise, drive, go shopping, etc. The needle examination may leave some small bruises but these usually resolve in a few days and will not interfere with your normal activities.