What is an EMG/NCV and what should I do to prepare?
Electrodiagnostic studies involve the recording of electrical signals generated by nerves and muscles. The analysis of these signals allows the physician to detect abnormal function in these tissues. These studies are, therefore, useful in evaluating disorders of nerve and muscle, which are often associated with complaints of numbness, pain, abnormal sensations, weakness, fatigue or cramps. They help the physician to arrive at the diagnosis and to determine the severity of the disorder. A variety of different procedures make up these electrodiagnostic studies. The two main procedures are Nerve Conduction Studies (NCV) and Electromyography (EMG). The type and number of procedures to be performed will be decided by the physician who performs the studies based on the suspected diagnoses.
Nerve Conduction Studies (NCV)
In these studies, nerves are stimulated by brief electrical stimuli and the responses generated are recorded using small electrodes applied to the skin. These stimuli will cause a momentary tingling sensation and may cause a muscle supplied by the nerve to twitch. The strength of the stimuli applied will be varied but they generally cause only a mild momentary discomfort. The responses recorded provide information about how well nerve impulses are conducted along the nerve.
Electrical signals generated by muscles are recorded during an EMG study using fine needle electrodes inserted into selected muscles. These signals, displayed on a screen and audible through a loudspeaker, are recorded with the muscle at rest and upon contraction. They help identify abnormal muscle function, particularly in diseases affecting the muscle primarily or in muscle weakness secondary to nerve injury. No electrical stimulation is applied in the study. EMG is well tolerated by most patients. The fine Teflon-coated needle causes only momentary discomfort. Occasionally, a sharp sting may occur which is stopped immediately by slight adjustment of the needle position.
Avoid applying lotions or ointments to the skin the day of your study. There is no need to restrict your activities before or after the test. Note the following precautions if they apply to you; otherwise, no special precautions are required.
Before Arriving for the Test
If you are taking blood thinning medications, such as Coumadin, or have a bleeding disorder, it may not be advisable to have an EMG, although nerve conduction studies are permissible. You should check with the prescribing physician to determine whether the blood thinner may be temporarily stopped to allow an EMG study. If you are referred for a diagnosis of myasthenia gravis, your physician may have to temporarily stop a drug called Mestinon to avoid it interfering with the studies. If you have a cardiac pacemaker or defibrillator, please make the office aware prior to your appointment so that the manufacturer of your device can be contacted to ensure that it is acceptable to perform the study and to determine whether any special precautions are necessary.