Medical treatments are changing rapidly, and high-resolution anatomical and functional imaging is constantly evolving. However, there is one seemingly insignificant test that plays an irreplaceable role in the diagnosis of epilepsy and is one of the most important tools in epilepsy treatment. This is known as the electroencephalogram (EEG).
The most important diagnostic tool for epilepsy – MRI and CT
Why do people with epilepsy need to have an EEG? The principle of epileptic seizures is very complicated. Simply put, it is the abnormal discharge of neurons in the brain, and EEG is the recording of this spontaneous and rhythmic electrical activity of brain cell groups through electrodes. Therefore, once a doctor suspects that a patient has epilepsy, or wants to rule out seizure-like disorders such as syncope or childhood migraine, he or she will request a further EEG.
CT and MRI are not interchangeable, and there is even less interchangeability between these two and EEG. MRI and CT mainly examine lesions in various organs of the body, the location of the lesions and the nature of the lesions, while EEG examines various bioelectric waves in the skull and brain to determine whether there are abnormal discharges through the bioelectric waveforms and indirectly diagnose the corresponding brain parenchymal lesions. In other words, MRI and CT examine tangible substances, while EEG captures invisible “waves”, so CT and MRI cannot replace EEG no matter how far they are developed.
No radiation, no magnetic field – EEG is quite safe
Some people think that EEG is an electrical examination of the head, so they worry that it will damage the brain tissue. This is a misconception. In fact, EEG is a graphical representation of the electrical current generated by the brain itself and traced out by the EEG instrument, which does not damage the human brain at all.
All living cells are constantly generating static electricity, called “bioelectricity”. This current is so small that it cannot be measured by ordinary methods, but after magnifying this bioelectricity millions of times, it can be drawn by a graphical line. If the drawing is of the brain, it is called an electroencephalogram. Similarly, there are electrocardiograms, electromyograms, and gastric electrograms. The ECG machine only magnifies a few thousand times, while the EEG machine has to be magnified hundreds of thousands of times because the brain is wrapped in a thick skull. Although the lines are curved, they are regular and scientific, so professionals can read it and make judgments of normal or abnormal based on it.
EEG is non-radioactive and non-magnetic, without any damage or discomfort. That is why it is important for epileptic patients to have their EEGs reviewed several times before diagnosis and during treatment. No matter how many times an EEG is done, it has no radiation hazard. Of course some discomfort caused by the child being trapped in bed while the EEG is being done, or the sticky electrodes being stuck tightly, are superficial discomforts that do not really affect the child’s health.
EEG should be done well – can’t be separated from “wake – sleep – wake”
At present, the major hospitals have three main types of scalp EEG examination.
1, routine EEG. Generally do about half an hour, the advantage is a short time, the child is easy to cooperate, the disadvantage is because the child seizure situation is different, if there is no abnormal discharge within half an hour, it is difficult to capture and record, so the current use is declining trend year by year.
2, dynamic EEG, also known as 24-hour EEG. It is usually the kind without video recording, and is mainly suitable for those who have relatively rare seizure frequency and whose seizures are not easily captured by short-range EEG recording; or whose seizures have been controlled and are ready to be reviewed before or after complete reduction of antiepileptic drugs (monitoring time is long and does not require sleep deprivation). The disadvantage is that it is difficult to diagnose because the images are not visible.
3. Video EEG (Video-EEG, VEEG). Also known as video EEG monitoring, it is a synchronized video device added to the EEG equipment to capture the clinical situation of the patient. The duration of monitoring can be flexible, ranging from a few hours to several days, depending on the condition of the equipment and the needs of the patient. However, in view of the increased cost due to longer monitoring time and the long waiting time for patient appointments due to limited resources, if the purpose of EEG monitoring is for epilepsy diagnosis and drug treatment without surgical procedures, an EEG that monitors for a few hours and records a more complete wake-sleep-wake process can mostly meet the needs of clinical diagnosis and treatment. At present, the length of EEG monitoring time set by each hospital is relatively fixed according to the actual situation, and the VEEG monitoring time at Peking University First Hospital is about 4 hours, during which most patients can record a complete wake-sleep-wake cycle (sleep deprivation is often required before monitoring, and those who still cannot fall asleep are given chloral hydrate to induce sleep if necessary). The positive rate is similar to that of 24-hour ambulatory EEG, and simultaneous video monitoring provides clinical information and is currently the most reliable test for the diagnosis of epilepsy.
The temporal principle of video EEG is to have a complete cycle from awake to sleep and back again. This is because some epilepsies are prone to discharge from waking to sleeping, some are discharging while asleep, and some are discharging after waking. So as long as this process is complete, even if it is only for one hour, it has a very high detection rate. If a child has been doing EEG for 12 hours with eyes open and not sleeping, it is about the same as doing it for 10 minutes, although not exactly the same, but the ratio is similar. Also a longer time would be more accurate, but the cost would be higher and the pain would increase if the child was stuck in bed too long. So, doing the wake-sleep-wake cycle is the most crucial.
As for what type to do, it is best to let the doctor decide.
How to do an EEG – playing with the phone is not allowed
After the outpatient visit, bring the “EEG Examination Request Form” issued by your doctor to the EEG ward for an on-site appointment. When making the appointment, in addition to being informed of the time to come for the chart, the child is reminded to have his or her head cleaned and hair cut as short as possible before the examination.
On the day of the examination, a parent will bring the child into the video monitoring ward. The reason for the parent’s presence is that, in addition to calming the child, the parent has additional tasks, such as helping the patient to call the police during a seizure and observing, recording and describing the patient’s behavior during the seizure and the information requested by the doctor. Monitoring with multiple parents can cause interference and unintentional obscuring of the video footage.
The EEG, with electrodes, is passed through an amplifier to which the electrodes are connected, and finally displayed through a computer. Video EEG, as the name implies, is a combination of EEG and video. The current trend is to have a dual-camera video EEG, with one filming the patient’s whole body to observe the overall seizure, and the other filming a partial one to better observe the subtle movements of the face and eyes during a seizure, such as smacking the lips and blinking the eyes.
It is important to emphasize that you should not play with electronic devices such as cell phones while having an EEG. Because EEG activity is a very weak bioelectric signal and thus requires millions of amplifications to be recorded on the scalp, non-EEG signals from various sources may also enter the amplifier and mix into the EEG signal during this process, called artifacts. It can interfere with the EEG results and create artifacts, especially when the phone is not connected in and other electronic devices are avoided as close as possible.
After the monitoring is completed, parents will be informed of the date when the official EEG report will be issued and can refer to this time to make an appointment with a clinician for the next step of diagnosis and treatment.
EEG doctors are crucial – reliable reports help in diagnosis
For the convenience of the patient, most hospital EEG labs give a formal written EEG report, along with several prints of the original graphs (usually 8 or 10 seconds on a sheet of paper) to generally reflect the main features of the patient’s EEG.
However, for a 4-hour EEG to be printed, it is almost impossible and unnecessary to print 1440 sheets with only one lead mode and fixed parameters to look at the graphs and print 10 seconds per sheet. Therefore, when the patient brings the EEG results for consultation, if the EEG report results are very reliable, the doctor can safely make a correct judgment based on the information provided by the EEG combined with the clinic, while if the EEG report description is unreliable and the printed graphs are not representative, at this time, even if the doctor himself has rich EEG reading experience, he can make a judgment based only on several EEG drawings selected by the original reader. Even if the physician has extensive EEG reading experience, he or she is often overwhelmed by the number of EEG drawings selected by the original reader. Therefore, a good and experienced EEG doctor can be a real clinical guide.
EEG – sensitivity and specificity should be known
EEG sensitivity refers to the incidence of epileptiform discharges in the epileptic population. It is influenced by a variety of factors, and not all patients with epilepsy have interictal epileptiform discharges monitored on EEG. In general, the incidence of epileptiform discharges is significantly higher in children with epilepsy than in adults, and the incidence is higher the earlier the age of onset of epilepsy.
The EEG specificity refers to the incidence of epileptiform discharges in the normal population compared to the epileptic population. 10% of the normal population may have non-specific EEG abnormalities and 1% of the normal population may have detectable epileptiform discharges, and the detection rate of epileptiform discharges is higher in children with neurological abnormalities without seizures. Treatment.
The role of the EEG should be properly assessed and should neither be underestimated nor exaggerated. The frequency of seizures is sometimes not proportional to the interictal EEG discharges, and the number of EEG discharges sometimes does not reflect the severity of the epilepsy, e.g., patients with benign Rolandic zone epilepsy often have a high number of central-middle temporal discharges during sleep, but the seizure frequency is often low and the prognosis is good.