Electrodiagnostic tests are performed to evaluate the function of the central (brain and spinal cord) or peripheral (nerves) nervous system and provide critical information to the physician about the functioning of the nervous system so a clear diagnosis can be made.
The following tests are performed by highly trained and skilled physicians and/or technologists, and are offered to both inpatients and outpatients:
Electroencephalagram (EEG) records the electrical activity of the brain. EEGs are performed on patients who have experienced seizures, epilepsy, passing out, headaches, or strokes. An EEG also can be performed to determine the level of consciousness of a patient, mental status changes, and for determination of brain death.
To perform an EEG, small metal disks are attached with a conductive cream to the scalp of the patient. The patient is asked to lie quietly for 20-30 minutes while data are being recorded. During the recording, the technologist will ask the patient to open and close his/her eyes, perform hyperventilation (breathing faster and deeper than usual), and go to sleep, if possible. These procedures enable the technologist to obtain detailed information for interpretation by the physician. The entire procedure, including patient set-up, takes approximately two hours.
Electromyography is used to assess the health and function of the muscles, and the nerves that control the muscles. It can be used to determine whether muscle weakness or numbness is caused by an injury, such as a "pinched nerve" or by an underlying neurological disorder.
When a muscle is at rest, it is electrically "silent." When a muscle contracts, it generates a variety of signals. During an EMG, the patient is asked to move the muscle, and the signals are detected by a small, sterile, disposable needle electrode, which is inserted through the skin into the muscle. The electrical activity in the muscle is displayed as waves on a computer screen, and may be heard on a speaker as crackles or pops. The presence, size, and shape of the waves indicate the ability of the muscle to respond to nerve stimulation and can help diagnose nerve or muscle damage.
Depending on what the physician is looking for, various muscles may be tested. The test normally takes 30-60 minutes to perform. This test may be performed on patients with a pacemaker.
Nerve conduction velocity (NCV) is a test of the speed of signals through a nerve used to diagnose nerve damage or destruction.
Patches called surface electrodes are placed on the skin over the nerve at various locations to record the nerve's electrical activity. The technician stimulates the skin over the nerve using a small handheld probe that delivers a small electrical impulse.
The nerve's resulting electrical activity is recorded by the electrodes. The distance between electrodes and the time it takes for the electrical impulses to travel between the electrodes are used to determine the speed of the nerve signals, and gives an indication of the health or disorder of the nerve.