SPORTS & SPINE ASSOCIATES
7756 Northcross Drive, Suite 203
Austin, Texas 78757
Phone: (512) 358-0500
Fax: (512) 358-0520
The term electrodiagnostic (EDX) refers to evaluation of the bioelectric activity of muscles and nerves. The test is done for the purpose of evaluating weakness, numbness, pain and symptoms such as fatigue, cramps and abnormal sensation. The two main procedures used to study nerves and muscles are the needle electromyography (EMG) examination and nerve conduction studies (NCS). The test usually takes approximately 30 to 60 minutes. Both studies may be performed, or only part of the EMG or NCS, depending on what the patient's complaints are and the findings of their physical exam. Electrodiagnostic testing must be specifically designed for each individual patient. The procedure is often modified during the examination, depending on the findings. The doctor that performs the electrodiagnostic testing in our office have had specialized training in the diagnosis and treatment of a wide variety of neuromusculoskeletal diseases. The interpretation of the electrophysiologic data is integrated with other data, such as history, physical exam and radiologic studies to make an appropriate clinical diagnosis.
In performing an EMG, the physician analyzes the electric activity in muscles by inserting a fine needle electrode into selected muscles. Needle electrode insertion requires a detailed knowledge of anatomy. It carries a small but finite risk of injury to anatomic structures (nerves, arteries) that can only be reliably identified by a physician who has had special training in this area of electrodiagnostic testing. Needle insertion may cause mild temporary discomfort. The needle is not used for injection and no shocks are given. The physician can determine whether the muscle or the nerve supplying it is functioning appropriately. The electric activity of the muscle is observed on a screen and heard over a speaker. The needles are discarded after use. Needle EMG is the only means for diagnosing pathology in a nerve or muscle. Surface EMG is a subjective, non-diagnostic type of testing. The doctor in our office does not perform Surface EMG, although it has other clinical applications.
During a NCS, the physician tapes small metal electrodes on the skin, applies a brief electric stimulus to one portion of a nerve. Nerve stimulation will cause a tingling sensation or muscle twitching. The physician can then evaluate the electric response of the nerve itself or muscle and determine if the nerve impulse is (a) conducted normally, (b) at a slow speed or (c) not transmitted at all. The type and configuration of the response can suggest what part of the nerve is damaged, and where.
Electrodiagnosis may also include evoked potentials. These studies use stimuli such as auditory clicks, a changing visual pattern, or small electric shocks applied to specific nerves. The recordings are made over the surface of the head and the spine to evaluate whether the sensory impulses are conducting normally through the nerves, spinal cord or brain. These studies are more sensitive for patients with sensory symptoms (numbness, visual disturbance, balance or auditory disturbance)
You do not need to do anything special to prepare for this test, except to keep the skin free of any lotions or emollients on the day of the examination. Be sure to inform our doctor if youre taking blood-thinning medication such as Coumadin, have hemophilia or a cardiac pacemaker.