The Neurodiagnostics Department supports your physician in the evaluation of neurological diseases and disorders. A complete range of neurodiagnostic procedures is performed on an inpatient and outpatient basis. Following is an explanation of various neurodiagnostic procedures.
An EEG is a recording of the electrical activity of the brain and is used to diagnose seizures, metabolic disorders, and infections of the central nervous system, head trauma, headaches, dizziness, numbness sensations and several other medical problems.
During an EEG, small metal discs (electrodes) are attached to the patient's scalp. The electrodes transmit the electrical activity of the brain to an instrument called an electroencephalograph, which amplifies the signals and records them on graph paper. After the test is complete, the recording is interpreted by a neurologist.
EEG testing usually takes about an hour. During a brief part of the test, the patient may be asked to breathe deeper and faster than usual. A strobe light, flashing at different speeds, may also be shown to the patient for a brief time. Awake and asleep EEGs are the most commonly performed neurodiagnostic tools. Wave patterns indicated by the EEG are analyzed, but not all variations from normal wave patterns indicate brain disease or injury.
While analyzing the results, the physician considers the patient's age and medical history. Sleep EEGs permit more in-depth monitoring of the electrical response of the brain. The early stages of sleep may produce various electrical abnormalities not detected in an awake EEG test. Patients having a sleep EEG are asked to refrain from sleep prior to the test time so they will easily become drowsy during the recording.
Evoked Potential (EP)
The evoked potential test is used to record specific electrical responses that the brain generates to stimuli. There are three major types of evoked potential tests performed at Texas Health Harris Methodist Hospital Fort Worth: auditory, visual and touch.
- Auditory: The auditory brainstem responses evaluate the auditory nervous system. Electrodes are attached to the patient's scalp and behind each ear. Auditory clicks are conducted through shielded headphones, which act as a stimulus for the auditory system and surrounding brain tissue. The brain responses are analyzed in terms of shape, size and occurrence.
- Visual: The visual EP test aids in the evaluation of the visual nervous system. Four electrodes are attached to the patient's scalp. The patient is asked to stare at a strobe light or a checkered pattern on a TV screen for a brief period. The light acts as a stimulus for the visual system and the brain and produces a measurable response.
- Touch: The somatosensory, or touch, evoked response test measures the time involved for a stimulus to be conducted from the extremities to significant nerve locations along the pathway into the spinal cord to the brain. Electrodes are attached to the skin and scalp at various points along the nerve pathway from the arms and legs to the brain. A mild electrical current is applied to the skin at the wrist and ankle. The electrical current serves as the stimulus during this testing procedure.
The monitoring of evoked responses during surgery is also used to determine nerve continuity during various operations. For example, during certain types of back surgery, the somatosensory evoked response test is used to verify that the spinal cord function is not being impaired and likewise with the optic or auditory nerves.
The EMG studies the electrical characteristics of nerves and muscles. The information can show injury or disease of the nerves and muscles. For example, if you have back pain because a slipped disc is pinching a nerve, the EMG can determine which nerve, severity of the injury and sometimes how long it has been pinched.
This helps your physician manage the problem either medically or surgically. The EMG is conducted with tiny Teflon-coated wire electrodes inserted into muscles at the site of the problem. The electrodes are so tiny that most patients cannot feel them, but the amount of discomfort is different in each patient. Any discomfort experienced is temporary. Sometimes instead of or with an EMG, the physician performs a nerve conduction study, which determines how fast the nerves conduct impulses. The nerve is stimulated and the response is recorded with the EMG machine. The result determines whether the nerves in your arms and legs are damaged. Patients can drive home and resume regular activities after the procedure. Please tell the physician whether you are taking any medications at the time of the procedure.
24-Hour Ambulatory EEG (AEEG)
Ambulatory EEG monitoring allows physiological data to be recorded continuously from people in their normal environment. As brain function disorders sometimes cannot be sufficiently detected by means of routine EEG investigations, AEEG monitoring offers the advantage of allowing the EEG to be recorded for long periods while patients are engaged in their everyday activities.
Recordings may be made from patients throughout their normal routine for periods of one or more days without causing discomfort, as the recorder is compact and lightweight. This technique has proved useful in many medical fields including neurology, pediatrics, psychiatry and neurophysiology. The investigation of seizures is the most widely used application of long-term ambulatory EEG monitoring.
A particular advantage of long-term recording is the ability to record during transient disturbances of brain function and the collection of quantitative data on seizure frequency. Even after careful clinical assessment, the nature and origin of a patient's attacks may remain unclear. Recording during the behavior in question is often the only way of resolving these problems. Ambulatory monitoring makes it possible to continue recording until a spontaneous attack occurs.
For more information, call 817-250-2072. For a physician referral, call 1-877-THR-WELL (1-877-847-9355). Office hours are 7:30 a.m. to 5 p.m. Monday through Friday, with and emergency on-call service available.