WHAT IS AN EMG?
Electromyogram (EMG), is a type of electrodiagnostic testing utilized to help the clinician determine if there is evidence of nerve or muscle injury that may be contributing to your symptoms. Standard electrodiagnostic testing involves two separate tests: nerve conduction studies and electromyography (electrical study of muscle).
WHY IS AN EMG PERFORMED?
There are often times when your doctor needs more diagnostic information to help guide treatment decisions and/or decide if you are an appropriate surgical candidate. The EMG test helps your doctor to clarify the cause of your symptoms by confirming and localizing the presence of nerve or muscle damage when exam findings and/or other diagnostic tests are not clear. The EMG often helps the provider to determine the exact location of the nerve damage, the severity of damage and provide information on when the injury may have occurred. This information is very useful when deciding between which best evidence-based medical treatments to offer you. For example, the information obtained from the EMG can help clarify which level in the spine to perform an epidural injection or whether there is a more urgent need for surgical intervention and which level(s) need to be addressed.
HOW IS AN EMG PERFORMED?
To perform the nerve conduction studies, the electromyographer will use a stimulating device to deliver an electrical impulse along the nerve being tested [Figure 1]. The delivered shock will feel similar to being stung by static electricity (some shocks may feel stronger than others). Your nerves are similar to telephone wires and they have the ability to transmit signals over long distances. The signal is then recorded and displayed on the computer screen for analysis.
After the nerve conductions are performed the electromyographer will perform a needle analysis of several individual muscles in your arm, leg and/or along the spine [Figure 1]. The needle is about the same caliber (diameter) as an acupuncture needle or sewing needle. The needle is specially designed to pick up electrical signals from muscle tissue. You will see and hear this electrical activity on the computer screen and your electromyographer will analyze the activity to determine if there has been any damage to the muscle tissue and/or the nerve supply to the muscle.
Figure 1: On the left is a picture of a typical nerve conduction study of the median nerve at the wrist. On the right is a picture of a typical needle EMG study of the abductor pollicis brevis muscle in the hand.
Combining the information from both tests (nerve conductions and needle electromyography) gives your clinician a great deal of insight regarding the health of your peripheral nervous system from the spine all the way to the tips of your fingers and toes.
WHAT ARE THE LIMITATIONS?
Electrodiagnostic testing cannot tell you what is causing the nerve and/or muscle damage. It can only confirm that there is evidence of damage. This is why EMG tests are often combined with other diagnostic tests such as MRI scans.
Also, although EMG tests are extremely helpful in finding evidence of nerve and muscle damage, they are not 100% diagnostic in all cases. Thus, if your test is normal this does not mean that your symptoms are not related to nerve injury. Your doctor will need to review the test results and determine if the information gained supports or refutes the diagnoses being considered. He will go over the results of the test with you, and he and will use the information gained to help make the diagnosis and offer appropriate treatments.
WHAT ARE THE RISKS?
In general, some parts of the test (electrical shocks during nerve conductions and needle sticks during the electromyography) may be a little uncomfortable. There is no risk of serious injury to the nerve or muscles from having this test done. The vast majority of patients who do experience an increase in their pain after the test do very well with simple pain management strategies (e.g. rest, ice, anti-inflammatories, or a short course of pain medicine).
HOW DO I PREPARE FOR THE DAY OF THE TEST?
Preparing for the test is easy. On the day of your test you may still wash your skin with soap and water, but don’t rub any topical lotions, moisturizers, sunscreens, creams, etc. on the arms or legs that are being tested. Also, if you are prone to having cold hands or feet (especially if the weather is cold) try to wear warm gloves or socks on the day of your test. The temperature of your limbs will affect the test results (warmer is always better in this case) and may save your examiner time trying to warm your extremities prior to the test.