Electroencephalogram (EEG) is the most important laboratory examination for the diagnosis of epilepsy, which is of great value not only for the diagnosis of epilepsy, but also for the classification of clinical seizures and the prognosis analysis of children. Epileptic discharges (spikes, spikes, etc.). ) is the most powerful basis for the diagnosis of epilepsy, and it is more meaningful to record the abnormal discharge during the attack. 29% ~ 55% adult epileptic patients can find epileptic discharge at the first EEG examination, and the positive rate can be increased to about 90% after repeated examination, and the positive rate of EEG in epileptic children is higher. Only a few children with epilepsy can't find abnormal discharge after repeated recording. If there are too many false negative EEG in children with epilepsy, we should pay attention to the following common reasons:
① The tracking time is too short. According to the minimum requirements of EEG operation technology, the recording time of routine EEG should not be less than 20 min.
② Insufficient understanding of the importance of sleep records. Most epileptic patients are more likely to record abnormal electrical activity in sleep records than when they are awake, while some epileptic discharges only appear in sleep records. Therefore, the EEG of sleep state (especially non-drug induced sleep state after natural sleep or sleep deprivation) should be recorded as much as possible, otherwise the positive rate will inevitably decrease.
③ Lack of knowledge about some non-spike and spike-like discharges. In addition to typical spikes, spikes or spike-slow complex waves, EEG abnormalities in children with epilepsy can also be manifested as other changes, such as explosive amplitude suppression, paroxysmal low voltage, monophasic release or slow wave burst. It is very important to understand these non-spike and spike-like abnormal discharges correctly to further improve the diagnostic value of EEG.
④ The influence of drugs. It is particularly noteworthy that some drugs that induce sleep may inhibit the occurrence of abnormal electrical activity, so drug-induced sleep recording should be avoided as much as possible. Although antiepileptic drugs may cause changes in the quantity, amplitude and waveform of abnormal electrical activity, which makes the EEG characteristics of some epilepsy atypical and affects the positive rate of EEG between seizures, it is not recommended to do EEG after stopping drug in clinic, because sudden withdrawal of drug may induce seizures or even status epilepticus. In addition, the improper setting of electroencephalograph and its recording parameters, and the lack of understanding of EEG characteristics of children by EEG technicians are also one of the reasons for the decrease of positive rate and the increase of missed diagnosis.
Second, EEG characteristics of different types of seizures
According to its clinical characteristics, seizures can be simply divided into two categories: full-scale seizures and local seizures. A small number of patients with atypical seizures, lack of specific description or necessary information, can be temporarily classified as various seizures with unknown classification (ILAE 198 1). This classification is mainly based on the observation and description of seizure symptoms, combined with the achievements of electrophysiology, nervous system structure and functional imaging, which provides a more scientific basis for the classification of various epileptic seizures. Electroencephalogram (EEG) is the most important objective basis for judging the type of attack, and different types of EEG have corresponding clinical characteristics. On the basis of careful understanding of the characteristics of epileptic seizures, careful EEG examination and analysis can significantly improve the accuracy of epileptic seizures classification. The main EEG features of common types of seizures are as follows (the attached figure is quoted from Liu Xiaoyan's Clinical Application of EEG in Children's Epilepsy and Clinical and Basic Research of Children's Epilepsy, edited by Qin Jiong, China Medical Electronic Audio-visual Publishing House, 2004).
1. Generalized tonic-clonic seizures (GTCS) have normal EEG background activities or nonspecific abnormalities. Abnormal waves such as spike wave, sharp wave, spike slow wave and multi-spike slow wave can be seen between attacks. Hyperventilation can induce the above epileptic waves to increase. A few may have photosensitive reactions. During the attack, the tonic phase of EEG began with the release of rhythmic spikes of 10 ~ 20 Hz, the amplitude gradually increased, the frequency gradually slowed down and gradually turned into slow spikes. Clinically, in the clonic phase, the frequency of slow spikes gradually slows down until it disappears. Transient electrical inhibition was observed after the attack, followed by diffuse slow wave activity, and background activity gradually recovered (Figure 1).
2. During the seizure of generalized clonus, the EEG showed rhythmic high-amplitude spinous slow waves and multi-spinous slow waves, and the voltage suppression after the seizure was generally light. Abnormal waves such as full-conduction or multi-focus spikes, sharp waves, slow spikes and multi-slow spikes can be seen between attacks.
3. During tonic attack, EEG showed a wide spike rhythm of 10-25 Hz, and its amplitude gradually increased. There is a lack of characteristic changes among epileptic seizures, abnormal background activities and epileptic discharges.
4. The EEG background activity of typical absence seizures is generally normal. Single or short bursts of 3Hz fully conductive slow waves can be seen between attacks, which can be limited to frontal lobe occasionally. Spine slow waves are often released more frequently during sleep than when awake, but they are mostly sporadic or fragmented, with irregular frequency and waveform, and local discharges can be seen, mainly in the frontal lobe area. Discharge during sleep generally does not cause seizures.
The EEG pattern during the attack is an indispensable condition for the diagnosis of typical absence attacks, which is characterized by bilateral synchronous symmetric spikes and 3Hz slow waves, and a few of them can appear multiple spikes and slow waves. Outbreaks start and end suddenly, lasting several seconds to dozens of seconds, mostly 5-20 seconds, which is easily induced by hyperventilation. The frequency of spike slow wave is slightly faster than 3Hz in the initial stage and slightly slower than 3Hz before the end (Figure 2).
5. The characteristic changes between spasms of spastic infants are high rhythm disorder (or peak rhythm disorder, Figure 3), background disorder, including slow wave and high amplitude spike wave, unsynchronized and unsynchronized. Focal spikes, multiple spikes and total conduction discharges appear alternately. It is obvious in slow eye movement sleep and disappears or is completely inhibited in rapid eye movement sleep. When you wake up and have a series of spasms, the peak rhythm disorder can disappear temporarily. Peak rhythm disorder is formed in early infancy and disappears in early childhood. A series of studies on the same patient can see the mutual transformation of EEG, such as neonatal burst suppression or Otahara syndrome, the peak obstacle of infantile spasm, and then the slow spike and slow wave of Lennox-Gastaut syndrome. A small number of infantile spasms lack the figure of peak rhythm disorder, which is mainly seen in the early stage of onset, but generally develops into peak rhythm disorder later.
During the attack, EEG showed full conduction sharp wave or slow wave, full conduction voltage decreased and activity was fast. Voltage drop is the most common EEG feature during seizures, which is found in 70% seizures.
6. The common EEG of myoclonic seizures is bilateral symmetric multi-spine slow wave bursts, and some of them may have photosensitive reactions (Figure 4).
7. There is no specificity in EEG during flaccid attack, and full conduction slow wave or multi-spine slow wave can be seen. During the attack, EEG is mostly full conduction slow wave or multi-spine slow wave burst, and there are also low amplitude or high amplitude fast activity and diffuse low voltage.
8. Focal Seizures During the onset of most focal seizures, abnormal electrical activities originating from the corresponding cortical areas can be seen on EEG, which can be manifested as various rhythmic activities with gradually increasing amplitude, and continuous irregular sharp waves or slow waves can also appear. Focal epileptic discharge can be seen between seizures. If the origin of discharge is deep, scalp EEG may not record abnormal discharge. The typical EEG manifestations of focal seizures are shown in Figure 5.
9. Secondary generalized seizures are local seizures. During the seizure, with the spread of abnormal discharge, the affected parts of the body gradually expand, and finally there is loss of consciousness, accompanied by generalized seizures. Various types of local epilepsy originating from different parts can be followed by complete seizures. At the beginning of the attack, EEG is a local epileptic discharge, and its position can often indicate the origin of the attack, and then gradually spread to the surrounding brain areas, and finally abnormal full conduction discharge appears.
In addition to the significance of judging epileptic seizures, EEG is also very important for the diagnosis of epilepsy syndrome. The basic elements of diagnosis of epilepsy syndrome mainly include onset age, clinical features of seizures, EEG features and neuropsychiatric state. Among them, EEG features play an irreplaceable role in the diagnosis of epilepsy syndrome, and some epilepsy syndromes have special EEG patterns, such as West syndrome with high rhythm disorder; Lennox-Gastaut syndrome: slow complex wave and slow rhythm wave during sleep: outbreak inhibition of Ohara syndrome, and so on. I hope that the majority of workers engaged in clinical diagnosis and treatment of childhood epilepsy will pay attention to learning and mastering.
Third, correctly understand the diagnostic value of EEG in children with epilepsy.
1. Epileptic discharge is not specific.
Epileptic discharge is most common in epileptic patients, but it can also be seen in other diseases and even healthy people, so its specificity is not high.
① Other brain diseases, such as tumors, cerebrovascular accidents, inflammation and degenerative diseases. Sometimes there is a transient seizure accompanied by epileptic electrical activity, which is a temporary and nonspecific abnormality.
② Epilepsy-like electrical activity can appear in EEG of a few psychotic patients, which is mostly related to the application of antipsychotics or sudden withdrawal of drugs. Such patients should be differentiated from patients with complex partial epilepsy whose main symptoms are mental symptoms.
③ About 1. 1% ~ 6.8% of healthy children have typical epileptiform discharges when they are awake, and the occurrence rate during sleep is 8.7%. Abnormal discharge mostly occurs in frontal lobe, followed by occipital lobe, and is rare in frontal lobe. However, with the increase of age, only 5.4% of children have clinical attacks, and most of the abnormal discharges disappear by themselves. It is suggested that this phenomenon may be related to genetic factors and some hidden brain dysfunction, and some may be the preclinical stage of idiopathic epilepsy. When there is no clinical attack, it should not be diagnosed as epilepsy or "occult epilepsy" and no antiepileptic drug treatment is needed. Follow up these children clinically, pay attention to whether they will have clinical attacks, and review EEG regularly. It is absolutely impossible to make a diagnosis of epilepsy easily based on an abnormal EEG report. Clinically, a few children with Tourrete syndrome can see typical spikes and slow waves on EEG, but the occurrence time has nothing to do with the symptoms of paroxysmal TIC, so TIC cannot be considered as epileptic seizure. Headache is also a common neurological symptom in childhood. Some children with migraine may also be accompanied by abnormal EEG or even typical epileptic discharge, which cannot be diagnosed as epilepsy. It is more difficult to make a clinical diagnosis of "viral encephalitis" according to the report conclusions of "mild abnormality" and "combined with clinical headache" in EEG.
2. Common factors affecting EEG results
There are many factors affecting EEG, some of which are even very sensitive. It mainly includes age development, genetic factors, state of consciousness and mental activity, drugs, etc. Developmental characteristics are the biggest difference between children's EEG and adults'. The younger you are, the more obvious the influence of age changes. Therefore, when analyzing children's EEG, we should pay special attention to age factors and developmental characteristics. Because of the uncoordinated EEG recording, children are prone to all kinds of false errors, such as electromyography (frowning, grinding teeth, chewing, swallowing and muscle spasm). ), electrocardiogram, blood vessel pulsation, breathing, blinking, exercise, sweating, ear electrode activation, alternating current interference, electrostatic or inductive interference, poor contact of electrodes or wires, etc. Some artifacts are similar to abnormal brain waves. If they are not identified and marked during recording, it will be difficult to judge them accurately afterwards. Making a wrong conclusion on EEG due to the inability to correctly identify artifacts will lead to mistakes in clinical diagnosis and treatment, and its harm is also great.
3. Comprehensive analysis of EEG examination results.
The EEG of epileptic patients should be analyzed from the following aspects.
(1) background activities: background activities have a certain relationship with the etiology of epilepsy. The background activity of general idiopathic epilepsy is within the normal range, while the background activity of symptomatic epilepsy is often abnormal. Focal epilepsy caused by organic lesions can be accompanied by local or asymmetric slow waves.
(2) Epileptic discharge between seizures: Typical epileptiform discharge generally refers to spike wave, sharp wave, spike slow wave, sharp slow wave and multi-spike slow wave. In addition, any wave or rhythm with amplitude, waveform or frequency protruding from the background and appearing repeatedly may be the performance of epileptic discharge. The discharges between seizures usually have typical waveforms. The frequency of generalized epilepsy-like discharge is helpful to diagnose epilepsy types, while partial discharge is helpful to locate the origin of epilepsy.
(3) EEG changes during the attack: EEG changes during the attack are more complicated, and some of them are completely different from the abnormal characteristics during the attack. In addition to the common abnormal discharge during the attack, it can also be manifested as sudden decrease of amplitude, diffuse irregular slow wave, single rhythm release and so on. In addition, movement or other artifacts are also common in EEG records during seizures, which should be closely analyzed in combination with clinical practice.
The recording and analysis of children's EEG is more difficult and complicated than that of adults, and its clinical application in children with epilepsy still needs to be improved. Pediatric neurologists should seize the time to actively learn the basic theory of EEG, cultivate the good habit of looking at pictures in person, be familiar with the characteristics of children's development, master the relevant norms of EEG technology for children, and EEG technicians should also strengthen their study, especially the relevant norms of EEG technology operation and the conclusive language of diagnosis reports, so as to provide more scientific and practical diagnostic information for clinicians. Let's work together in Qi Xin to further improve the diagnostic level of epilepsy in children.