Electromyography (EMG) and nerve conduction studies (NCS) are two very common tests that go hand-in-hand. Often the two are referred to collectively as an “EMG test”. Unlike an X-Ray or MRI, which show anatomy, these tests give vital information about muscle and nerve function. These tests are part of a group of tests called “electrodiagnostics”. They involve small electrical impulses that are generated by the body, picked up by wires, and fed to a computer. A specially trained physician uses a computer monitor, sophisticated filters amplifiers to determine the function of the involved muscles and nerves. Health care providers have used these tests for over 50 years.
What is an EMG?
Electromyography is a way of studying muscles to determine whether or not they are receiving normal nerve supply. A small needle, similar in size to an acupuncture needle, is inserted into the muscle being studied. When the muscle contracts, it gives off electrical impulses that can be characterized as normal or abnormal in shape and pattern. A muscle can also give off signals at rest. Each muscle is supplied by specific nerves, and these nerves arise from specific levels of the spinal cord. Seeing the pattern of muscles involved, it can be determined which nerve is having a problem. Thus, the needle EMG test can determine the location of a problem. Additionally, each muscle gives off signals that yield information about how severe a problem is, and how long it has been present.
A common problem detectable by needle EMG is radiculopathy. This is a condition where a nerve is pinched as it exits the spine. By showing abnormalities in the group of muscles supplied by that particular nerve, the diagnosis can be established.
What are Nerve Conduction Studies?
Nerve conduction studies (NCS) are tests that determine whether or not the nerves being tested are
conducting properly. To assess the nerves with this test, small electrodes are placed on the skin over the area being investigated. An electrical impulse is delivered by a stimulator a short distance away from the electrodes. This stimulation does feel like a small shock, but is generally a strange rather than a painful sensation. No “shock” actually travels down the nerve. Instead, the stimulation causes the nerve to fire, and the nerve conducts its own impulse. This impulse is then received by the electrodes. A series of sophisticated electronics with filters and amplifiers processes the impulses. The doctor conducting the test can interpret things such as the strength and speed of the conducted impulse. These results reflect the health of the nerve. Not only can an abnormality be found with this test, but it can also be
characterized as to the nature, location, and severity of the problem.
A common problem that can be defined with NCS is carpal tunnel syndrome (CTS). In CTS, a nerve traveling through the tunnel within the wrist can become entrapped, causing pain, numbness, and tingling. NCS can determine if the nerve conducts its impulse with abnormally slow speed through the carpal tunnel, and whether or not the size of the impulse is reduced, helping confirm the diagnosis.
What About the Needles?
The needles used are sterile, and are discarded after the examination is complete. Needles used in the past were larger and uncomfortable. They had to be sterilized after each use. New technologies have allowed development of the products used today. They are disposable, very small, and designed to slip beneath the skin with minimal discomfort.
Do I need an EMG/NCS?
If you present to your health care provider with symptoms of pain radiating from your neck or back, or pain, numbness, tingling, or weakness in an arm or a leg, it is important to determine the cause. There can be many different causes of these symptoms. EMG/NCS can be helpful in establishing the
diagnosis and extent of the problem, so that proper treatment can ensue. Depending on the condition, the proper treatment may be no treatment at all!
How should I prepare for the test?
There is really very little preparation necessary. The physician will appreciate it if you are not wearing excessive lotion, as this will prevent adherence of the tape used to attach the electrodes. Let the physician know if you are taking blood thinners, although they will probably not prevent completion of the study. If your prescribing physician does not object, oral nonsteroidal anti-inflammatory medications such as Advil, ibuprofen, or similar medications may be stopped five days before the test, to minimize bleeding. Medications will not likely affect test results.
What can I expect on test day?
As with any healthcare appointment, if you become sick prior to the study, let the office know so that you may be rescheduled.
Usually, you will be asked to get into a gown for the test. This is to allow the physician access to the areas required. Usually, both NCS and EMG will be included in the electrodiagnostic testing. The NCS portion will involve some mild shocks, but this should not be severe. The EMG portion will involve
needle insertion into the muscle being examined, but generally is not too uncomfortable. When the test is underway, the physician will want to know if you are in significant discomfort.
How can I get the results?
Preliminary results can usually be discussed upon completion of the exam. Final results will require full analysis of the data, and creation of a report. This report will be sent to your health care provider, usually within a week. Your referring physician will make further medical recommendations.