WHAT IS EEG?
Electroencephalography (EEG) is a test used to detect brain electrical waves in patients with epilepsy and suspected seizure disorders. EEG device is used to measure the electrical activity of the brain. The purpose of EEG in epilepsy is to support the diagnosis, classify, investigate focal brain lesion and monitor epilepsy patients. In EEG, recordings are taken from many points on the head with cables called electrodes. It can be likened to a heart electrocardiogram (ECG). It is a process that requires more technical care and generally takes longer to record since it is trying to record currents at much lower voltages.
IN WHICH DISEASES EEG IS REQUIRED?
* Diagnosis and follow-up of epilepsies.
* Evaluation of age-appropriate cerebral electrical maturation
* Some psychiatric evaluations
* Some rare disorders (SSPE, intoxications)
WHAT ARE EEG PREPARATIONS?
The head is clean
The absence of substances such as gel or spray in the hair
The stomach is full
Having a comfortable clothing
orlon should not be made of wool type materials
. It should not have received anesthesia on the day of EEG recording.
HOW IS EEG APPLIED?
EEG process is done by Technician or Technicians.
In the process performed by the EEG Technician or Technician, the points where the EEG electrodes will be placed on the head and between the scalp are preferably measured according to the international 10-20 system. Afterwards, usually 20-25 electrodes are attached. Routine recording points can be increased up to 32 electrodes to take advantage of the 32 channels found in today’s widespread digital systems. During the recording, it is tried to ensure that the patient is in a comfortable environment and, if desired, to see the sleep and wake periods. Additional activation methods, usually intermittent light stimulation and rapid breathing, are routinely used.
Simultaneous video recording during EEG has now become a routine practice. The aim here is to compare with the simultaneous EEG changes in some suspected movement or seizure-like situations and make a decision. In addition, it is useful to clarify the relationship between EEG and some movements that may be encountered unexpectedly.
It was first used in the 1940s and revolutionized neurology in its time. With electroencephalography (EEG), fluctuations in the spontaneous electrical activity of a large group of neurons are recorded from the surface. This method reflects the current functional state of the brain rather than its structural features. Therefore, despite the developments in structural imaging methods (such as CT, MRI), it still maintains its importance. Especially in cases where there is no pathological finding reflected in structural examination methods, the importance of EEG increases even more.
EEG is the most important examination method after clinical findings in the diagnosis of epilepsy and in the follow-up of epileptic patients. It is also a very important additional research method for many brain diseases such as encephalopathy and encephalitis. In some special conditions (for example, some slow virus diseases and hepatic encephalopathy), it can give very precise clues for the clinical diagnosis.
Recording of EEG
EEG is a completely painless and harmless examination method. Most of the electrical potentials recorded from the scalp are the result of the interaction of the total excitatory and inhibitory synaptic potentials in the pyramidal cells with the extracellular ion currents. These electrical potentials, which are normally very weak, are recorded by electrodes placed on the scalp and amplified by amplifiers. The points where the electrodes will be placed are determined according to the international 10-20 system. Records taken from all of these points are evaluated with connections called montage (Figure 1). In old-style EEG devices, the current recording is printed on paper and its parameters cannot be changed later. However, the most important advantage of digital EEG devices used today is the ability to switch to other montages after the recorded montage, the amplitude and other parameters are readjusted for each case and for each finding, providing the most reliable information.
Figure 1. The placement of the standard electrodes according to the international 10-20 system and the longitudinal bipolar mounting, also called “double banana”, are shown schematically with arrows. The same electrodes must be considered with a transverse mounting and also as unipolar (for example, by connecting to CZ or ear electrodes that are not in the figure).
A routine EEG capture takes about 30 minutes, before the placement of the electrodes is a very important preparatory step. The electrodes are placed by gluing with suitable materials or squeezing with rubber bands in the form of a hat, and their conductivity is ensured with some special pastes or salt water. These metal particles called electrodes are connected to the EEG device with a thin wire. It is important that the patient’s hair is clean before the EEG recording. In addition, since some changes in hunger can be seen, the patient should be full during the shooting. During the EEG recording, the patient should sit calmly. According to the instructions of the EEG technician, he should close and open his eyes. It is also very important that the EEG filters are set correctly, the preferred high frequency or “low pass” filter is considered 70 Hz and the low frequency or “high pass” filter is 0.5 Hz, the EMG filter can be turned on if necessary.
Hyperventilation (HV) is applied in every routine EEG recording. The aim here is to activate an epileptic focus. There may be cases where HV cannot be applied for some medical reasons. These can be summarized as recent cerebrovascular disease, severe cardiopulmonary disease, and sickle cell anemia. HV may not be applied for reasons such as the patient’s unconsciousness and lack of cooperation. The HV duration is a minimum of 3 minutes and should preferably be applied for 5 minutes. Triggering absence seizures or the appearance of generalized spike-wave paroxysms with HV is very typical (Fig. 2). HV reaction, which is seen under 16 years of age and characterized by generalized slowing down, is a picture that should be well known. Reporting this physiological reaction as pathological can lead to adverse outcomes for the patient. In addition, focal slow wave and focal epileptiform activity can also be activated by HV. If HV is not performed, very important diagnostic information will be lost. In addition, it should be kept in mind that metabolic problems such as hypocalcemia and hypoglycemia may also be activated during HV and this may disrupt the EEG.
Figure 2. The patient shows 3 Hz generalized spike-wave discharges lasting 12 seconds, clinically accompanied by a diving seizure, triggered by hyperventilation.
Intermittent photic stimulation (IFS) is likewise an important activation method that must be applied in every routine EEG. In some cases, epileptic activity can be seen only in IFS, while the entire EEG is normal. Sometimes even myoclonic seizures and, more rarely, other seizure types (absence, occipital partial seizure or generalized tonic-clonic seizure) may occur. It should not be forgotten that there may be sensitivity in IFS in completely asymptomatic cases. IFS should start at least 3 minutes after HV and overlap with the HV effect should be avoided. The patient should be positioned so that the distance of the nasion point to the photic stimulator is 30 cm and it is right in the middle. The illumination of the environment should neither be too bright nor too dark to see the patient; that is, an illumination that can be called dim is required. The recommended European standards for IFS frequencies to be used are as follows: 1,2,4,6,8,10,12,14,16,18,20,®60,50,40,30,25. Each stimulus should be applied for 10 seconds and repeated after a break of at least 7 seconds. In the first 5 seconds of the ten-second period, stimulation should be performed with the eyes open and the patient’s eyes should be closed, and light stimulation should continue for 5 seconds with the eyes closed. The duration of this procedure in a patient is a maximum of 6 minutes. When a generalized response is clearly seen, the stimulus should be discontinued by the technician, because in some cases, prolonged light stimulus can lead to generalized convulsions. The reporter must be well acquainted with the benign or physiological responses (photic driving and photomyoclonic) seen in IFS. The increase in photosensitive seizures triggered by factors such as TV and computer in recent years increases the importance of this issue.
Evaluation of EEG
In order to evaluate EEG findings, it is necessary to know the normal EEG characteristics very well. Basic activity is evaluated before each EEG recording. Normal basic activity differs markedly with age, wakefulness, and some physiological states such as hunger. Activity that is considered normal for a three-month-old baby is pathological for a 3-year-old. Similarly, the EEG activity of an adult who is in deep sleep can mean a serious pathological finding when the same person is awake.
There is symmetry between the hemispheres of the brain in EEG, so it is important to compare the two hemispheres. Apart from this, the most important problem when evaluating EEG is to distinguish artifacts. Artifacts are the result of various mechanical-electrical potentials included in the EEG recording but not originating from the brain (such as eye movements, movement and muscle artifact, electrode slippage, sweating) (Figure 3). Some artifacts that an experienced person can recognize immediately can easily be mistaken for pathological brain activity.
Figure 3. Eye closure artifact limited to the frontal regions marked with arrows should not be confused with delta waves.
The drugs used by the patient during EEG and metabolic problems, if any, must be recorded. Because the effects of some drugs and metabolic conditions on EEG are evident. In addition, the time between the seizure of the epileptic patient and the EEG recording, that is, whether the EEG is performed in the postictal or interictal period, is important for the interpretation of some findings.
When interpreting the results of EEG, it is necessary to define the findings and not to make an incorrect ascription between the EEG finding and the clinical diagnosis. EEG evaluation should be done by experienced specialists, but every physician should be able to interpret the results.
Major EEG Findings
EEG shows potentials at various frequencies and amplitudes (Figure 4). Although the basic activity varies according to age, an activity with a frequency of 8-12 Hz is observed in the parieto-occipital regions in a normal adult when awake and eyes closed, this activity is called alpha activity. Alpha activity is lost or suppressed when the eyes are opened. Beta activity is a rhythm with a frequency of 13-25 Hz that is evident in the frontal and central regions. High amplitude beta activity usually suggests the use of a sedative-hypnotic drug.
Figure 4. The frequencies of some EEG waves are shown.
During normal sleep, 5 different periods are observed in the EEG. The first period is the transition period between sleep and wakefulness. As the alpha rhythm disappears, it is replaced by low-voltage slow activities, then high-amplitude sharp waves appear in the vertex region. An inexperienced eye may interpret this period as pathological, assuming that it occurs during wakefulness. The sign of the second period is 12-14 Hz sinusoidal sleep spindles located in frontocentrally (Figure 5). The third and fourth periods, called slow wave sleep, consist of high amplitude, diffuse and irregular slow waves. The REM (rapid eye movement) period is a low-voltage, variable-frequency activity and is the period in which dreams are seen and rapid eye movements and muscle atony are recorded. Because it appears approximately 90 minutes after the onset of REM sleep, it is not usually seen in short-term sleep studies performed during the daytime.
Figure 5. Sleep spindles (arrow) and generalized K complex are seen in fronto-central regions.
Pathological findings that can be observed in EEG are divided into two main groups as nonspecific slow waves and epileptiform activity. Slow wave activity is grouped into theta (4-7Hz) and delta (1-3Hz). The localization of the slow wave seen is important. Its frequency, amplitude, and other related factors, if any, are recorded (Figure 6). Epileptiform anomalies are spikes (with bases below 70ms) and sharp (with bases of 70-200ms) waves, and the physiological event underlying these waveforms is paroxysmal depolarization shift (Figure 7). Slow wave and epileptiform anomaly may coexist. However, it is known that typical epileptiform EEG anomalies can be seen in normal individuals (1.5-5% in normal children). On the contrary, only slow waves can be seen in the EEG examination of an epileptic patient, and the examination may even be completely normal. In this respect, the physician evaluating the EEG should avoid directing the clinician to a diagnosis.
Figure 6. The replacement of alpha waves, which is a normal activity during hyperventilation, with theta and even delta waves is considered normal until the age of 16, but it is pathological in an adult patient.
Figure 7. Epileptiform activity consisting of generalized irregular spike-wave discharges is observed in a patient with juvenile myoclonic epilepsy.
Other EEG Techniques
Apart from routine EEG, frequently sleep EEG (especially since wakefulness recording is difficult in children), long-term EEG, sleep deprivation EEG, aiming to trigger the epilepsy focus, basically the same but with some time and situation differences can be planned. The method called EEG “mapping” is based on the principle of mapping the frequencies of EEG waves and is not used because it has been shown that it is not superior to visual analysis.
Apart from these, simultaneous recording of the patient’s video image and EEG examination has become a very important method, which is used more and more frequently. In this method, which is called video-EEG monitoring, the patient’s image and EEG are recorded simultaneously and the findings can be compared in a much more detailed way. This method is mainly used to distinguish epilepsy from situations that mimic it, to precisely determine the seizure type, and to observe the semiological features accompanying the seizure. One of the most important and frequent reasons for use is to determine the responsible epileptogenic focus by recording seizures in cases resistant to drug therapy and to prepare for epilepsy surgery. In this sense, video-EEG monitoring is indispensable for epilepsy surgery. When focus cannot be demonstrated with noninvasive, that is, superficial video-EEG, an approach can be determined for that patient with the help of detailed clinical and imaging analyzes and invasive EEG can also be performed. In invasive video-EEG, stereotactic deep electrodes or subdural “grid” and “strip” electrodes are placed in the brain parenchyma according to the status and location of the epilepsy focus in the patient. These techniques differ from noninvasive EEG in that they carry risks, especially infection and bleeding. The term semi-invasive includes electrodes placed at the level of the foramen ovale. It is applied infrequently because it is very painful and does not have much superiority. Interpretation of video-EEG requires a serious knowledge of ictal EEG and clinical seizure semiology, so it is reasonable to perform it in epilepsy centers. Another issue in which video-EEG is very useful in clinical practice is the recognition of psychogenic non-epileptic seizures or pseudo-seizures. A patient with pseudo-seizure is prevented from taking unnecessary anti-epileptic drugs with a misdiagnosis, and it is possible to plan the right treatment. On the contrary, it can be seen that what is thought to be a pseudoseizure is actually an epileptic seizure. This is especially true in seizures originating from the frontal lobe.
In patients with sleep problems, various types of sleep disorders are recorded by polysomnography examination and an accurate diagnosis and treatment approach is provided. In addition to the EEG, the patient’s breathing, eye and extremity movements are also recorded here. This examination is an indispensable diagnostic tool for sleep apnea, which poses a serious danger to the patient (See also: Sleep disorders).
Clinical Use of EEG
Clinical diagnosis can be confirmed by characteristic epileptiform EEG findings in epileptic patients. According to EEG findings, seizure type and epilepsy syndrome can be grouped. However, it should be kept in mind that a normal EEG will not be sufficient to exclude the diagnosis of epilepsy. While typical pathological findings are seen in only 30-50% of epileptics with the first routine EEG, the rate of pathological findings increases to 60-90% with the third EEG and provocation methods (Figure 8). Another very important point is that the agreement between even experienced EEG readers is only 70%, that is, the interpretation of EEG shows serious subjectivity.
Figure 8. Generalized type epileptiform activity during intermittent light stimulation (marked as photic 15) occurred during stimulation with 15 Hz when routine exposure was completely normal and constituted a valuable clue in terms of diagnosis.
Although EEG alone does not make a decision, it provides very useful information in the decision to start treatment or in cases where treatment is planned to be terminated in a patient who has had the first epileptic seizure. Having EEG pathology is a risk factor for seizure recurrence, but it should not be perceived as the only determinant.
In the Epilepsy section, specific EEG findings of various epileptic syndromes are discussed (See: Epilepsy). When the seizure-free family members of epileptic cases are examined, typical epileptiform findings can be observed.
In a routine EEG, seizure recordings can be made from time to time. Therefore, it is important to know the ictal EEG patterns in detail. A rare situation is that the patient may have an electrophysiological seizure recording when there is no clinical seizure. EEG monitoring is very important in status epilepticus, it is known that there are different seizure patterns for status epilepticus (Figure 9). For the diagnosis of nonconvulsive status epilepticus, EEG is an indispensable and definitive diagnostic method (Figure 10).
Figure 9. In a case whose status epilepticus lasts for days, the variability of EEG findings at different times is observed.
Figure 10. Findings proving non-convulsive status epilepticus are observed in the EEG of the patient, who was admitted for strange behaviors and sleepiness.
Although the main area of use of EEG is to evaluate epilepsy patients, another patient group for which it is very important and indispensable is cases in which the possibility of encephalitis or encephalopathy is emphasized in the emergency outpatient clinic. Here, EEG easily distinguishes a psychiatric behavior change from an encephalitis-related picture. Some EEG findings, such as periodic lateralized epileptiform discharges (PLED), are combined with clinical findings and are of great value in making the diagnosis in conditions that require rapid diagnosis and treatment, such as Herpes simplex encephalitis (Figure 11). The PLED sign usually reflects an acute and devastating brain lesion and is significantly associated with seizures. In intoxications and metabolic events, EEG is helpful in detecting and severity of brain dysfunction, as well as in the monitoring process. Although metabolic encephalopathies give similar nonspecific signs of slowing down, a typical EEG finding, namely triphasic waves, is seen in hepatic encephalopathy, which has a significant diagnostic value (Figure 12). Sometimes triphasic waves may accompany other toxic-metabolic encephalopathies.
Figure 11. This patient with periodic lateralized epilpetiform discharge (PLED) on the left hemisphere was diagnosed with Herpes simplex encephalitis. Slow waves are also seen in the right hemisphere of the patient (odd numbered electrodes point to the left hemisphere, even numbered ones point to the relevant regions of the right hemisphere.)
Figure 12. Typical triphasic waves are seen in a hepatic encephalopathy case
Focal slow wave finding suggests the presence of a structural brain lesion in the region where it was recorded with a probability of 70%. However, this finding can sometimes be seen in a non-lesional focal epilepsy. Focal voltage reduction is similarly a finding in subdural and epidural deposits, as well as suggesting a lesion in the relevant gray matter. In the examination of space-occupying lesions, EEG has lost its importance today and has left its place to structural imaging methods. However, sometimes it is necessary to apply to EEG to investigate the epileptogenic potential of the space-occupying lesion. Similarly, EEG has lost its importance in cerebrovascular diseases. Focal slowing is observed in approximately half of the cases in transient ischemic attacks. A patient with a marked acute deficit but with a completely normal EEG has a high probability of lacunar stroke. EEG is not required in patients with migraine and other primary headaches unless there is an additional problem. Slow wave activity is typical in EEG in a special picture called Handle (a headache with temporary neurological deficits and lymphocytosis in CSF).
EEG is used to examine and monitor brain function in degenerative brain diseases. While EEG is normal at the beginning in Alzheimer’s disease, alpha activity is replaced by diffuse theta activity in advanced stages of dementia, usually within 3 years. Generalized voltage reduction is noted in some conditions, such as Huntington’s disease. If there is typical EEG finding in Jacob-Creutzfeldt disease, it is pathognomonic in terms of diagnosis (Figure 13). However, this EEG finding may disappear in advanced stages and may be replaced by a diffuse, severe slowing. Similarly, EEG gives pathognomonic findings in subacute sclerosing panencephalitis (SSPE) (Figure 14). The main feature here is the repetition of the generalized discharge consisting of slow waves and sharp elements added at periodic intervals during the shooting. Since SSPE is still seen in our country, it should be investigated whether there is a periodic feature when such paroxysms are encountered.
WHAT IS EEG?
WHERE IS EEG DONE?
HOW IS EEG DONE?
• Routine (Standard) EEG
• Routine (standard) EEG in children and infants
• EEG in short sleep and EEG in all night sleep
• Video-EEG Monitoring
• Invasive Video-EEG Monitoring
WHAT SHOULD YOU CONSIDER BEFORE EEG EXAMINATION?
WHAT IS EEG?
Electroencephalography is the process of evaluating the electrical activity of the brain. Electrical signals related to nerve cells (neurons) in the brain tissue are transmitted to the scalp on the skull by “volume conduction”. These signals are transferred to a special amplifier with electrodes placed on certain areas of the scalp. The signals amplified in this amplifier are evaluated by a neurologist trained in this field with the help of a computer and EEG program. Certain changes occur in brain electrical signals in epilepsy, degenerative brain diseases, central nervous system infections, psychiatric and neuropsychiatric diseases. By interpreting these changes, very valuable information is obtained that helps physicians make decisions in the diagnosis of diseases and in monitoring the effectiveness of the treatment applied and the course of the disease. In addition, in some cases such as slow virus diseases and hepatic encephalopathy, quite definite conclusions can be reached with EEG for clinical diagnosis.
WHERE IS EEG DONE?
• EEG is the most important examination method in the diagnosis of epilepsy, determining the epilepsy type, monitoring the clinical process and the effectiveness of the treatment applied.
• It is used in the diagnosis of neurological diseases that cause consciousness and perception disorders, coma, forgetfulness, attention disorder or dementia, and to monitor the clinical process and the effectiveness of the treatment applied.
• It is useful in detecting neurological or neuropsychiatric factors that may be present in some psychiatric disease states.
• It is used to detect some sleep disorders such as narcolepsy (sudden sleep attacks).
• It is one of the basic methods used in the detection of brain death in coma patients in intensive care units.
• EEG monitoring is used to monitor the electrical activities of the brain in patients under general anesthesia during cardiovascular surgery or neurosurgery operations, where cerebral circulation and brain functions are likely to be affected.
• EEG monitoring is performed in making the decision for surgical treatment and determining the type of surgical intervention to be applied in patients with epilepsy resistant to drug therapy.
• A helpful examination method in determining if a person has a problem or condition that affects their brain function or mental health.
HOW IS EEG DONE?
For purpose, the form of the examination can be planned as routine EEG, short-sleep EEG or all-night sleep EEG, Video-EEG monitoring, Invasive Video-EEG monitoring, and ambulatory EEG.
• Routine (Standard) EEG
It is the most commonly used EEG examination method. An EEG recording is made by the EEG technician for approximately 30 minutes in a patient who is awake. It is a process that takes about one to one and a half hours in total, including pre-record preparations, EEG recording time, and post-recording procedures. This recording is then evaluated by the neurologist and an EEG report is prepared on the day of the shooting or within one day. Before the EEG recording, the recording electrodes are placed by the EEG technician at the points determined according to the standard 10-20 system on the scalp with an EEG paste, which is a conductive adhesive material. Collodion is used for bonding in cases where long-term recording and EEG electrodes need to be fixed. These electrodes are connected to special input points on the EEG recording box, which enable the technician to transfer the EEG signals to the recording computer. It is important for the recording quality that the patient’s hair is clean before the EEG recording, and that there is no conditioner, hair lotion, gel or spray that may prevent electrical conductivity on the scalp. Since some changes can be seen in the EEG recordings in case of fasting, the patient is asked to be full during the examination. During recording, movements in the patient’s head and eyes, swallowing movements, contractions in the head and jaw muscles, and excessive sweating cause electrical signals called “artifacts”. Artifacts interfere with the EEG signals and cause the quality of these signals to deteriorate. Therefore, during the EEG examination, the patient is asked to remain as still, calm and relaxed as possible. However, if there are movements defined in the patient, they are marked on the EEG recordings by the technician. EEG signals change with the opening and closing of the eyelids. During the EEG examination, EEG recording is required in both cases. According to the wishes of the recording technician, the patient is asked to open and close his eyes and these are noted on the EEG recordings by the technician. Some methods applied during EEG recording increase the likelihood of signal changes seen in neurological disease states. These are called “activation methods”. “Intermittent photic stimulation” and “hyperventilation” are two activation methods applied during almost every routine EEG recording. Hastanın “uzun süre uykusuz” bırakıldıktan sonra EEG kaydı elde edilmesi ise bazı durumlarda başvurulan ve EEG de saptanması beklenen anormal sinyallerin ortaya çıkması olasılığını artıran aktivasyon yöntemlerinden biridir.
Aralıklı ışık uyarısı “fotik stimulator” adı verilen bir ışık kaynağı ile uygulanır. Bazı epilepsi tiplerinde yalnızca aralıklı ışık uyarısı sırasında epileptik aktivite görülebilir ve kimi durumlarda miyoklonik nöbetler, absans nöbetler, oksipital parsiyel nöbetler ve jeneralize tonik-klonik nöbetler ortaya çıkabilir. Hiç epileptik nöbet geçirmemiş kişilerde bile (özellikle yakınlarında bazı epilepsi tipleri olan normal kişilerde) aralıklı ışık uyarısı ile epileptik sinyaller ortaya çıkabilir. Aralıklı ışık uyarısı ile hiperventilasyon arasında her iki yöntemin etkilerinin birbiri üzerine eklenmesini engelleyecek kadar uzun bir zaman farkı (en az 3 dakika) bırakılır. Standart aralıklı ışık uyarısı frekansları 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, ®60,50,40,30,25. Her uyarı 10 saniye boyunca uygulanır ve en az 7 saniye ara verildikten sonra diğer uyarıya başlanır. On saniye sürenin ilk 5 saniyesinde gözler açık, kalan 5 saniyesinde gözler kapatılarak uyarı verilir. Jeneralize bir epileptik aktivite ortaya çıktığında hastanın epilepsi nöbeti geçirmesine neden olmamak için uyarı teknisyen tarafından sonlandırılır.
Hiperventilasyon için hastadan en az 3 dakika süre ile hastadan derin soluk alıp vermesi istenir. Hastanın bilinç durumunun yeterli olmaması, kooperasyon yetersizliği ya da hastanın çok küçük yaşta olması gibi nedenlerle hiperventilasyon yapılamayabilir. Ayrıca yakın zamanda geçirilmiş serebrovasküler hastalık, ciddi kardiyopulmoner hastalık ve orak hücreli anemisi olan hastalarda hiperventilasyon yapılmaz. Hiperventilasyon sırasında fokal yavaş dalga ve fokal epileptiform aktivite ya da absans nöbetleri ve jeneralize diken dalga paroksizmleri ortaya çıkabilir.
Kimi durumlarda EEG kaydından önce hastanın uzun süre uykusuz kalması istenir. Genellikle epilepsi olduğu düşünülen, ancak rutin EEG incelemesinde epilepsi tanısını kanıtlamaya yeterli bulgu saptanamayan durumlarda hastanın uzun süre uykusuz kaldıktan sonra rutin EEG incelemesinin tekrarlanması istenebilir.
• Çocuklarda ve bebeklerde rutin (standart) EEG
Küçük yaştaki çocuklarda (genel olarak 6 yaşından küçüklerde) kayıt sırasındaki hareketlilik ve istenen talimatlara uyum gösterememeleri nedeniyle uyku sırasında EEG kaydı elde edilir. Kayıt süresi olabildiğince uzun tutulmaya çalışılır (mümkün ise en az 1 saat). Hasta uyandırıldıktan sonra hareketlerin EEG kaydına engel olmadığı dönemde olabildiğince uzun bir süre uyanık dönemde de EEG kaydına devam edilmeye çalışılır. Bebeklerde ve çocuklarda normal EEG kayıtları yetişkinlerden oldukça farklıdır. Bebeklerin ve çocukların beyin işlevlerinin gelişmelerine paralel olarak EEG kayıtlarında belirli dönemlere uygun değişiklikler olur ve yaklaşık 16 yaşından sonra erişkin tipte EEG paterni ortaya çıkar. Bebeklerde ve çok küçük yaştaki çocuklarda uykuda EEG kayıtları çok daha değerlidir ve bu nedenle bir EEG incelemesi mümkün ise en az 1 saat uykuda EEG kaydı içermelidir.
• Kısa süreli uykuda EEG ve tüm gece uykuda EEG
Epilepsi hastalarının önemli bir bölümünde rutin EEG ya da uzun süreli uykusuzluk sonrasında EEG kayıtları normal kalabilir. Rutin EEG incelemesi normal bulunan epilepsi hastalarının büyük çoğunluğunda uykuda kayıtlarda EEG bozuklukları saptanır ve epilepsi tanısı kanıtlanabilir. Klinik olarak epilepsi olduğu kuvvetle düşünülen hastalarda rutin EEG incelemesinin normal bulunması durumunda uyku sırasında EEG kaydı istenebilir. Hastayı izleyen hekimin kararına göre, özellikle rutin EEG incelemesinin normal bulunacağı tahmin edilen ya da uykuda epilepsi nöbetleri tanımlanan hastalarda rutin EEG yapılmadan, doğrudan kısa süreli uykuda EEG ya da tüm gece süresince uykuda EEG incelemeleri istenebilir. Kısa süreli uykuda EEG ve tüm gece uykuda EEG incelemelerinin başında mutlaka uyanık dönemde rutin EEG kayıtları elde edilir ve bundan sonra hasta yatağa yatırılır ve uyumasına izin verilerek incelemeye devam edilir. Kısa süreli uykuda EEG incelemesinde 2-3 saatlik uykuda kayıt ardından hasta uyandırılır. Tüm gece uykuda EEG incelemesinde gece boyunca hastanın uyumasına izin verilir ve kayıtlara devam edilir. Kısa süreli ve tüm gece uykuda yapılan incelemelerde gerekli olduğu durumlarda EEG elektrodlarına ek olarak göz hareketlerinin kaydı için göz çukurlarının yan taraflarına göz elektrodları, çene kaslarının kasılmasını kayıtlamak için çene ucuna çene elektrodları, bacak hareketlerinin kaydı için bacak kasları üzerine bacak elektrodları ve kalp ritminin kayıtlanması için göğüs üzerine EKG elektrodu yerleştirilerek poligrafik kayıtlar elde edilir.
Video-EEG Monitörizasyonu
Gerekli görüldüğü durumlarda poligrafik kayıtlarla eş zamanlı olarak hastaların video görüntüleri de kayıtlanabilir. Kısa süreli ya da tüm gece uykuda EEG kayıtları sırasında poligrafik kayıtlarla eş zamanlı olarak hastaların video görüntülerinin de kaydedilmesi istenebilir. Özellikle uykuda ortaya çıkan ve tekrarlayan bazı olayların epileptik olup olmadığının belirlenmesi ya da epileptik olmayan uyku bozukluklarından (parasomnilerden) ayırt edilmesi istendiğinde hastaların eş zamanlı video görüntüleri kayıtlanır.
Bazı durumlarda (seyrek ortaya çıkan ve niteliği belirlenemeyen epileptik, psikojenik ya da kardiyovasküler nöbetlerin ayırt edilmesinde) uzun süreli video-EEG monitörizasyonu gerekli olabilir. Bu gibi durumlarda nöbetlerin ortaya çıkmasına yetecek kadar uzun bir süre (bazı durumlarda bir gün ya da birkaç gün boyunca) EEG ve video görüntülerinin eş zamanlı kayıtlanması gerekebilir.
Video EEG monitörizasyonu epileptik nöbetleri, epilepsi olmayan ancak epilepsiye benzeyen durumlardan ayırt etmek, nöbet tipini kesin olarak belirlemek ve nöbete eşlik eden semiyolojik özellikleri gözlemlemek için kullanılır. Video-EEG monitörizasyonuna en sık başvurulan durumlardan biri de ilaç tedavisine dirençli epilepsi hastalarında epileptik nöbet sırasında EEG ve video kaydı yapılarak sorumlu epileptojenik odağın beyindeki yerleşiminin belirlenmesidir. Epilepsiye neden olan odağın epileptik aktivitesinin cerrahi girişimle kontrol altına alınması (epilepsi cerrahisi) için epileptik odağın yerleşiminin belirlenmesi gereklidir. Bu nedenle epilepsi cerrahisine hazırlık aşamasında video-EEG monitörizasyonu mutlak gerekli olan bir incelemedir.
İnvazif Video-EEG Monitörizasyonu
Epilepsi cerrahisine hazırlık aşamasında yüzeyel (non-invazif) EEG elektrodları ile yapılan Video-EEG monitörizasyonunda epileptik odağın gösterilemediği, odak yerleşiminin kesin olarak saptanamadığı durumlarda ya da birden fazla odak olasılığı ortaya çıktığında uygulanacak cerrahi girişimin biçiminin belirlenmesi için dolğrudan beyin dokusu üzerine yerleştirilen EEG elektrodları ile nöbet kayıtları yapılması gerekli olabilir. Yüzeyel elektrodlarla yapılan Video-EEG monitörizasyonundan elde edilen lokalizasyon bilgilerine ek olarak, klinik ve radyolojik görüntülemelerin sonuçlarının ayrıntılı analizinden elde edilen bulgular değerlendirilerek beyin dokusunun belirli bölgelerine stereotaktik derin elektrodların veya subdural “grid” ve “strip” adı verilen matriks elektrod sistemlerinin yerleştirilmesi planlanır. Bir ön cerrahi girişim ile kafatasında önceden belirlenen yerlere delikler açılarak bu deliklerden beyin dokusu üzerine strip elektrodlar ya da beyin dokusu içine derin elektrodlar yerleştirilir ya da gerekli durumlarda kafatası kemiğinin bir bölgesi kaldırılarak grid matriks elektrodlar yerleştirilir. Bu operasyondan sonra yeniden yapılan radyolojik incelemeler ile yerleştirilen elektrodların beyin bölgeleri ile ilişkileri kesin olarak belirlenir. Daha sonra bu elektrodlar aracılığı ile yeniden nöbet kayıtları elde edilir. Bu sonuçlar epileptoloji ve invazif monitörizasyon konusunda deneyimli bir nöroloji uzmanı tarafından yorumlanır, epileptik odak ya da odakların kesin yerleşimleri belirlenmeye çalışılır. Sonuçlar epilepsi cerrahisi girişimini yapacak olan nöroşirürji uzmanı ile birlikte değerlendirilerek uygulanacak cerrahi girişimin biçimi ve sınırları belirlenir. Bu yöntemlerin belirli oranlarda infeksiyon, kanama gibi komplikasyon riskleri bulunur. Bu nedenlerle, invazif EEG monitörizasyonu tümüyle bir ekip çalışması gerektiren bir işlemdir ve bu uygulamaların epilepsi cerrahisi merkezlerinde yapılması gerekir.
EEG İNCELEMESİ ÖNCESİNDE NELERE DİKKAT ETMELİSİNİZ ?
• EEG incelemesi acil durumlar dışında genellikle randevu verilerek yapılan bir incelemedir. Yapılacak inceleme yöntemine göre incelemenin süresi değişir. Rutin EEG bir ila bir buçuk saat kadar süre alır. Buna karşın kısa süreli uyku EEG 3-4 saat, tüm gece uykuda EEG 7-9 saat zaman alır. Epilepsi cerrahisi hazırlığı için yapılacak EEG monitörizasyonu ise günler sürebilir. Bu nedenle size yapılaması istenen inceleme yöntemine göre zamanınızı önceden planlamanız önerilir.
• Açlıkta kan şekerinin düştüğü durumlarda EEG de düzensizlikler ortaya çıkabilir. EEG incelemesinin acil durumlar dışında tokluk durumunda yapılması tercih edilir.
• Yapılacak işlemlerde derinizin elektriksel iletkenliği önemlidir. Bu nedenle, saçlarınızın temiz olması, EEG öncesinde sabun ya da kremsiz şampuan ile yıkanmış olması önemlidir. Saçlarınız yıkadıktan sonra saç kremi, saç spreyi, jöle vb uygulamayın.
• EEG kayıtlarınız değerlendirecek elektrofizyoloğun rapor oluşturma aşamasında durumunuz ile ilgili bilgilere ihtiyacı olacaktır. Bu nedenle doktorunuzun size verdiği EEG istek formunu ve durumunuzla ilişkili önceden yapılmış olan incelemelerin raporlarını (radyolojik incelemeler, laboratuar incelemeleri ve önceki EEG incelemelerinin sonuçlarını) yanınızda getiriniz.
• Bazı durumlarda rutin EEG incelemesinin uzun süre uykusuzluk sonrasından yapılması istenebilir. Sizden bu tür bir inceleme istenmişse randevu saatinizden önceki 18-24 saat boyunca uyumayın.
• Acil ve zorunlu durumlar dışında EEG incelemesinden bir gün öncesinden itibaren alkol. uyku ilacı ya da sakinleştirici (sedatif, anksiyoloitik) ilaç kullanmayın. İncelemeden önceki 6 saat içinde kahve içmemeniz tercih edilir.
• Uykuda EEG incelemesi, yapılacaksa yanınızda pijamalarınızı ya da rahat uyuyabileceğiniz bir giysinizi ve kişisel bakım eşyalarınızı getirin. Uykuda EEG incelemesi yapılacaksa, inceleme sırasında kolayca uyuyabilmeniz için inceleme öncesinde uzun bir süre uykusuz kalmanız gerekmektedir. Kendinizin uyku alışkanlığına göre inceleme öncesinde yeterli bir süre uykusuz kalın.
• Kullanmakta olduğunuz ilaçları yanınızda getirin ya da isimlerini bir kağıda not alın. Epilepsi tedavisi görmekteyseniz, size aksi söylenmedikçe epilepsi ilaçlarınızı kullanmaya devam edin.
• Saçlı deriye yapıştırılan elektrotlarla yapılan EEG incelemesi tümüyle zararsız bir inceleme yöntemidir.
• Çocuklarda inceleme sırasında tepki ve kooperasyon eksikliği olabilir. Bu nedenle EEG incelemesi bir çocuğa yapılacaksa, incelemeden önce uygun bir biçimde çocuğun bilgilendirilmesi, korkusunun azaltılması için güler yüzlü ve anlayışlı bir tavırla olabildiğince güven verilmesi uygun olur. Ayrıca, küçük yaştaki çocuklarda EEG incelemesi her zaman uykuda yapılır. Bu nedenle inceleme için size verilen randevu saatinden öncesinde çocuğunuzun yeteri kadar uzun bir süre (tercihan en az 6 saat) uykusuz kalmasını sağlayın.
