Understand the diagnostic process in Clinical Neurophysiology. Learn about EEG preparation EMG procedures and what to expect during diagnostic testing.
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Diagnosis and Imaging
The evaluation for epilepsy or altered mental status often begins with an EEG. Preparation is simple but important. Patients are asked to arrive with clean dry hair free of oils or sprays as these can interfere with the sensors. They should continue taking their prescribed medications unless told otherwise. Sometimes the doctor wants to record sleep so the patient may be asked to stay awake most of the night before the test to ensure they fall asleep during the recording. Caffeine should be avoided on the day of the test.
During an EEG the patient sits in a comfortable chair or lies on a bed. A technician measures the head and marks spots for the electrodes. Small metal discs are pasted onto the scalp using a conductive paste. This is painless. The patient is asked to relax and lie still. They may be asked to open and close their eyes breathe deeply and rapidly or watch a flashing light. These activities can trigger abnormal brain waves. The test typically lasts twenty to forty minutes.
For an EMG and nerve conduction study no special preparation is usually needed other than keeping the skin clean and free of lotions. Patients should inform the doctor if they are on blood thinners or have a pacemaker. Loose comfortable clothing is recommended. The test is usually done in two parts the nerve conduction study and the needle exam. It is important to eat a normal meal beforehand and stay hydrated.
The nerve conduction study is the first part of the EMG visit. The doctor or technician tapes small electrodes to the skin. They use a stimulator to deliver a small electrical shock to the nerve. This feels like a static static shock from a doorknob. The electrodes record the response of the nerve. This measures how fast and strong the nerve signal is. Multiple nerves in the arms or legs are usually tested. While the shocks are surprising they are not harmful and the sensation stops immediately.
The second part is the needle examination. The doctor inserts a very thin sterile needle electrode into specific muscles. This needle acts like a microphone to hear the electrical activity of the muscle. There are no shocks involved in this part. The patient may feel a pinch when the needle goes in and some pressure. They will be asked to relax the muscle and then tighten it. The doctor listens to the sounds and watches the screen. This part is crucial for finding nerve damage.
Evoked potentials test the central nervous system pathways. For visual evoked potentials patients should bring their glasses or contacts. No eye drops are used so vision is not blurred afterwards. For auditory evoked potentials the ears should be clean. For somatosensory evoked potentials which test the feeling pathways comfortable clothing is best. The patient simply sits or lies down while stimuli are presented.
During visual testing the patient watches a checkerboard pattern shifting on a screen. Electrodes on the head record the brain’s response. During auditory testing the patient wears headphones and hears clicking sounds. For somatosensory testing small electrical pulses are applied to the wrist or ankle. The computer averages the brain’s response to these repetitive stimuli to create a wave. These tests are generally painless and require the patient to be relaxed and attentive.
A sleep study or polysomnogram requires an overnight stay in a sleep lab. Patients should bring comfortable pajamas and toiletries. They should avoid napping on the day of the study. The room is usually private and designed to look like a bedroom. Sensors are applied to the head face chest and legs. This setup takes about an hour. The patient is then allowed to go to sleep. A technician monitors the recording from another room all night.
Before a surgery that requires monitoring the neurophysiologist or monitoring team may review the patient’s history. They need to know about any pre existing nerve deficits so they can establish a baseline. The patient meets the team on the day of surgery. Small needle electrodes are placed in the scalp and muscles after the patient is under anesthesia. There is no pain or memory of this for the patient but it provides a safety net during the operation.
The diagnostic tests in Clinical Neurophysiology are extremely safe. EEG and evoked potentials are non invasive and carry no risk. The electrical shocks in nerve conduction studies are low voltage and safe even for patients with heart conditions though pacemakers require special care. Needle EMG carries a very small risk of bleeding or infection similar to a blood draw. There are no lasting side effects from the electricity used. The primary goal is to gather information safely to guide treatment.
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No, imaging shows structure while neurophysiology shows function. Both are used together for accurate diagnosis.
Yes, functional abnormalities may be present even when imaging appears normal. Neurophysiology detects electrical dysfunction.
They are used for diagnosis, localization, disease classification, and monitoring functional changes over time.
No, many structural findings are incidental. Functional correlation determines clinical significance.
Diagnosis requires clinical correlation. Test results support but do not replace neurological assessment.
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