Electroneurodiagnostics is the study and recording of electrical activity in the brain and nervous system. The tests are performed by technologists who record information on paper or computer, and the results are interpreted by a specially trained physician. The following explains some of the most common tests.
An EEG records the electrical activity of the brain. Highly sensitive monitoring equipment records the activity thorough electrodes that are placed at measured intervals on a patient's scalp. This test is not painful for the patients. Electrodes are placed on the scalp with a paste-like substance and usually take about an hour while the patient remains still, relaxed and comfortable. During the test, the patient may be asked to take repeated deep breaths (hyperventilate) and may be shown a strobe light that flashes at different speeds. Both activities can help reveal different brain patterns that are useful for diagnosis. Sometimes, physicians want to observe brain patterns that occur during sleep. For sleep tests, the patient may be asked to stay awake most of the night prior to the EEG appointment.
The EP is a recording of electrical activity from the brain, spinal nerves or sensory receptors in response to specific external stimulation. Electrodes are applied to the scalp and other areas of the body, a series of stimuli is introduced and a computer records the neurological responses. Hundreds of responses are received, amplified and averaged by a computer. The final response is plotted on a graph and interpreted by a physician who looks for particular waveforms and the time it takes them to occur.
The three most common types are the brainstem auditory evoked potential (BAEP), the visual evoked potential (VEP) and the somatosensory evoked potential (SSEP).
Auditory: The BAEP assists in evaluating the auditory nerve pathways from the ears through the brainstem. Electrodes are attached to the scalp and earlobes, and earphones are placed over the ears. The phones deliver a series of clicks or tones to each ear separately.
Visual: VEPs evaluate the visual nervous system form the eyes to the occipital (visual) cortex of the brain. Electrodes are applied to the scalp, and the patient is usually asked to stare at a pattern on a video screen while remaining fully alert. Each eye is tested separately.
Somatosensory: SSEPs assess pathways from nerves in the arms or legs through the spinal cord to the brainstem or cerebral cortex. Electrodes are placed on the scalp and along the spinal cord, and a small electrical current is then applied to the skin overlying nerves on the arms or legs. The current creates a tingling sensation but is not painful. Each leg or arm is tested separately.
The Ambulatory EEG records brain activity for 24 hours on a small digital recorder that is worn around the waist. Electrodes are applied to the scalp with a glue-like substance, and the patient is sent home with a diary to record activities and any symptoms during the 24 hours. You must wear a button down shirt for this test so the electrodes do not interfere when you get home with your clothing. The equipment is returned the very next day and your results are interpreted by the physician.
Electromyography (EMG) is a test of a muscle's electrical activity. It is used to test how a muscle responds to signals from the nerves responsible for muscle movement. An EMG may also include a test of how fast the motor nerve conducts impulses-this is the nerve conduction study (NCS) or nerve conduction velocity (NCV) test. Loose clothing should be worn for this test and please do not apply lotions or creams anywhere on your body the day of the test, as this could interfere with the testing.