Electroencephalography, EEG
Electroencephalography, EEG is the most useful and frequently performed test used to diagnose epilepsy. It works by measuring the electrical activity created by neurons close to the scalp. Theoritically the neurons (nerve cells) communicate through chemical and electrical pathways enabling cellular functions. The electrical charge of lots of neurons working together simultaneously near the scalp is recorded by the EEG and is represented as waveforms on a graph.
Many different waveforms have been understood and can be interpreted to demonstrate either normal or abnormal electrical brain activity. Many epilepsy syndromes have been found to produce distinctive waveforms making it possible to characterize epileptic seizures from other conditions, as a result abnormal electrical activity is often categorized as epileptiform and non epileptiform.
The test involves a technician or medical expert/assistant placing a set of small metal electrodes on the scalp with a special adhesive (usually a washable adhesive or conductor gel). These electrodes are connected to the monitoring equipment where real time recordings are taken of electrical brain activity.
The usual recording time for an EEG is 30-60 minutes and the test involves nothing more than the electrode placement making it speedy and also safe. The data obtained should be read by skilled personnel such as a neurologist with specialized training in EEG interpretation. Routine EEG testing is done as an outpatient.
However there are some limitations of scalp EEG which are;
- The test is time sensitive as it captures in real time only.
- Data can only be obtained from the areas of the brain closest to the scalp, therefore seizure activity deep within the brain is may not being captured properly.
- The test quality result greatly depand on subject or patient co-operation.
To overcome these limitations scalp EEG monitoring is added to video telemetry for an extended time and a more detailed look at seizure activity. Areas of the brain that are not close to the scalp are monitored using Intracranial EEG techniques which can be painful for some people.
Video Telemetry
Video EEG telemetry involves recording brain activity and the physical manifestations that accompany the seizure. The information collected helps to give a more accurate diagnosis of the types of seizures experienced which in turn leads to the most appropriate treatment being implemented.
Video EEG monitoring requires a hospital stay of usually 4-7 days. Scalp electrodes are placed and secured with a special adhesive, placement of the electrodes will be checked 24 hours daily by an EEG technician. Usually a skull cap will be worn for the duration of the testing therefore hair washing is not possible during this time.
A video camera is running simultaneously with the EEG, it is important to stay in view of the camera to gather all the necessary data, for this reason the individual must stay in the designated hospital room whilst recording is taken place. A specially equipped private room is provided for this type of testing.
Under medical supervision seizures are provoked. This is done by seizure medications being carefully tapered down by your neurologist and seizure triggers such as sleep deprivation and exercise being initiated.
Safety measures such as padded bed rails are applied. A catheter (venous cannula) is inserted into a vein, usually in the arm or hand. If needed intravenous antii-seizure medications can be administered via this catheter to stop seizures.
Data from video EEG telemetry can help the neurologist differentiate from epileptic and non epileptic conditions, determine the types of seizures experienced and where in the brain they begin.
This clinical service is for the prolonged EEG-Video Monitoring, for epileptic patients refractory to medical treatment linked to the Epilepsy Surgery that is being developed at our department/ward. It is designed to observe patients at optimum levels for medical assistant and trained nurses to observe and to interact with the patient.
This service using an EEG-Video prolonged monitoring service with detection of epileptiformed events performed on-line; contributing to a better definition of the clinical pattern, which allows to determine the presence of Graphic-EE for the surgical treatment of evaluated patients.