What Are Electrodiagnostic Studies?
Electrodiagnostic studies are used to study nerves and muscles and are helpful in evaluating weakness, numbness, pain, and symptoms such as fatigue, cramps and abnormal sensation. They include the needle electromyography (EMG) examination, nerve conduction velocity (NCV) studies, and evoked potentials.
During an EMG, the physiatrist analyzes the electrical activity of muscles by inserting a fine needle electrode into selected muscles. Needle insertion may cause mild temporary discomfort. The needle is not used for injection and no shocks are given. By doing this the physiatrist can determine whether the muscle or the nerve going to the muscle is/are working normally by seeing the electrical activity on a screen and listening to the sounds of the activity on a speaker. The needles are discarded after each patient to prevent the transmission of infections.
To perform nerve conduction velocity studies (NCV), the physiatrist tapes small metal electrodes on the skin, applies a brief electric stimulus to one portion of a nerve, and reads the response to the stimulus at a different place along the nerve. Nerve stimulation will cause a slight tingling sensation. The physician can then evaluate the electrical response of the nerve or muscle to which the nerve is attached and determine if the nerve impulse is (a) conducted normally (b) at a slow speed, or (c) not transmitted at all, suggesting damage to a nerve.
Preparation for Electrodiagnostics
You do not need to do anything special to prepare for the electrodiagnostic study except keep your skin free of any lotions or emollients on the day of the study. There are no restrictions relative to activities before the test. Be sure to inform the office, however, if you are taking blood-thinning medication such as Coumadin, have hemophilia or a cardiac pacemaker, or use a TENS unit. Patients with myasthenia gravis should ask whether or not to take anticholinesterase medication on the day of the study. There are no permanent after effects.
Time Required
The time required to complete an electrodiagnostic study varies, but generally takes approximately 45 – 60 minutes.
Differences Between Electrodiagnostic Studies and Other Diagnostic Studies
Electrodiagnostic studies are unlike other studies such as x-rays or EKG’s which have predetermined designs and are often “performed” by technicians and “read” by physicians afterwards (i.e. radiologists and cardiologists). Electrodiagnostic studies are designed, performed, and “read” by the physiatrist; and are designed according to your specific situation. For example, although a common problem such as tingling and numbness in the hand and arm may be studied in a similar way by many electrodiagnostic physicians, there is no single, universally-accepted specific protocol or set of procedures to be followed.
After taking your history and examining you, but before performing the electrodiagnostic study, Dr. Bernal develops a working diagnosis, which may be different or may modify the diagnosis with which you were referred. This working diagnosis is fluid and may change as the electrodiagnostic study proceeds. Dr. Bernal designs the study based on this working diagnosis before he begins your study. He is continually assessing the findings encountered during the performance of the test. The findings may require him to alter the test design from what he had planned to do at the beginning of the test, or even 5 seconds earlier!
Although Dr. Bernal is usually able to arrive at a final diagnosis after the completion of the study, often times this is not possible.
A report is sent to your referring physician, who will be in a better position than before the electrodiagnostic consultation to coordinate further treatment based on the Dr. Bernal’s findings and recommendations.
Why Can’t My Internist or Family Practitioner Perform Electrodiagnostic Studies?
Electrodiagnostic studies should only be performed by either a physiatrist or a neurologist because these specialties undergo special training during their residencies and fellowships in the diagnosis and treatment of neuromuscular diseases and in the application of particular techniques to the study of these disorders. Additionally these specialties are trained in using the patient’s history and physical examination to plan the course of the electrodiagnostic study; and are widely considered the only experts to perform such studies.