What are they? How are they done?
What is Electrodiagnostic Testing?
The term “electrodiagnostic testing” covers a whole spectrum of specialized tests, two of which are the electromyogram and the nerve conduction study. Many problems involving nerves or muscles require electrodiagnostic testing to provide information. Although they are different tests, the electromyogram and the nerve conduction study go hand in hand giving vital information regarding your nerve and muscle function.
What is Electromyogram (EMG)?
An electromyogram (EMG) is a diagnostic study that has been used by health care providers for over 50 years. An EMG provides information about the integrity of the muscles and the nerves in your body. An EMG examination is typically ordered by a physician to evaluate for muscle or nerve damage as part of a medical workup.
Using a computer, monitor, amplifier, loudspeaker, stimulator and high tech filters the examiner actually sees and hears how your muscles and nerves are working. As part of the EMG a very small needle is inserted into various muscles in the arm, leg, neck or back where you are having symptoms. In many cases the examination will include areas far from where you are having symptoms because nerves can be very long.
A clean new needle is used on each examination, and the needle is thrown out after the examination is complete. There is virtually no chance to catch any diseases from having an EMG. Also, because the needle used is sterilized, the chance of infection is minimal. An EMG is only one part of nerve testing; another part is called the nerve conduction study.
What is a Nerve Conduction Study (NCS)?
A nerve conduction study (NCS) is one part of a comprehensive nerve and muscle diagnostic test. Like an EMG, a NCS is typically ordered by a physician to evaluate for muscle or nerve damage as part of a medical workup. Once again, the examiner uses a computer, monitor, amplifier, loudspeaker, stimulator and high tech filters to monitor the functioning nerves and muscles in your body.
The examiner places small electrodes on your skin over muscles being tested in your arms or legs. The examiner then uses a stimulator to deliver a very small electrical current to your skin near nerves being tested, causing your nerves to fire. The electrical signals produced by nerves and muscles are picked up by the computer, and the information is interpreted by a physician specially trained in electrodiagnostic medicine. The stimulator only produces a very small shock that does not cause damage to your body. Many different motor and sensory nerves are typically evaluated.
Do I Need an EMG/NCS?
When you go to your health care provider with symptoms including radicular pain (pain radiating from the neck or back), numbness, weakness or tingling in an arm or leg, it is important to find out what is causing your symptoms. There are many possible causes or the above symptoms, and many cases resolve spontaneously on their own. However, if symptoms persist, an EMG/NCS is one way to assess muscle and nerve function and is often used with other testes such as MRI or CT scan that create images of the body.
What Can EMG/NCS Detect?
The EMG/NCS examines nerves from just outside the spinal cord to the skin. Nerves have long projections called axons that carry electrical signals. Axons are surrounded by supporting cells called Schwann cells, which produce myelin. Myelin acts like an insulator for the axons and makes nerve signals travel faster.
In addition, because nerves go into muscles and give signals to muscles causing muscle contraction, the EMG/NCS also tests muscles. Abnormalities with the peripheral nervous system (all nerve tissue outside the brain and spinal cord), including the insulating myelin and muscles, can all be evaluated with EMG/NCS. While EMG/NCS can detect many different problems with nerves or muscles, some of the more common are covered below.
Cervical or Lumbar Radiculopathy
A radiculopathy is the term used for pain radiating from the neck (cervical) or low back (lumbar). There are many causes for radiculopathy; one is herniated discs. The intervertebral discs are one of the weight bearing structures in the neck and back. These discs can become degenerated and can herniated, pressing on nearby nerves and causing the radiating pain. Often, herniated discs squeeze nearby nerves as they pass causing damage. An EMG/NCS can evaluate the severity of the nerve damage due to discs.
Many common medical conditions like diabetes can cause nerve damage. In such cases, the longest nerves are usually affected first; hence the name peripheral neuropathy. Whether the diabetes is controlled with diet, oral or injectable medications, there is often nerve damage. An EMG/NCS can evaluate the severity and monitor any progression of a peripheral neuropathy.
A myopathy is a disease that is localized to the muscle and muscle supporting structures. Myopathies are hereditary (inherited from the mother or the father) or acquired (from affection or underlying medical condition). A patient will usually present with proximal muscle weakness and perhaps myalgias (muscle aches). An EMG/NCS can localize the disease process in such cases and aid diagnosis.
A focal neuropathy is when a single nerve suffers damage at a specific sight along its course. There are an infinite number of possible focal neuropathies in the body, but the most common example is carpal tunnel syndrome. Carpal tunnel syndrome is when the nerve to the hand is squeezed at the wrist causing numbness, tingling, pain, and weakness. An EMG/NCS evaluates the severity and location of such focal neuropathies.
What Can I Expect on the Day of the Test?
As mentioned earlier, the electrodiagnostic testing usually includes both the electromyogram (EMG) and nerve conduction studies (NCS). The EMG section includes a small sterilized needle being inserted in the muscles to be tested. There is some discomfort with needle insertion, but most tolerate the testing without difficulty. You may notice some bruising after the needle portion of the examination, ice to sore areas can help with discomfort and limit the bruising. Any time the skin is penetrated with at needle, there is a theoretical risk of infection developing.
The NCS portion of the examination includes a small stimulus applied near nerves to make them fire. In most cases a series of shocks are necessary to get the optimal response. Any discomfort is transient, and the stimulus is not strong enough to cause damage to the body.
When are the Results Ready?
After EMG/NCS testing, the examining physician must analyze the data and combine all the information into a report. The electrodiagnostic examination report will be added to your medical record and a copy sent to the referring physician. The time for report generation varies from lab to lab, but generally is no more than a few days. Be sure to follow up with your health care provider.
Disclaimer: This information is for general information and understanding only and is not intended to represent official policy of North American Spine Society.. Please consult your physician for specific information about your condition.