Electroencephalography with epilepsy

Epilepsy is a disease manifested by two or more epileptic seizures (seizures). An epileptic attack is a short, usually unprovoked, stereotyped disorder of consciousness, behavior, emotions, motor or sensory functions, which even in clinical manifestations can be related to the discharge of an excessive number of neurons in the cerebral cortex. The definition of epileptic seizure through the concept of the discharge of neurons determines the most important value of EEG in epileptology. Specification of the form of epilepsy (more than 50 variants) includes an obligatory component description of the characteristic pattern of this form of EEG. The value of EEG is determined by the fact that epileptic discharges, and consequently, epileptiform activity, are also observed on the EEG outside the epileptic attack.

Reliable signs of epilepsy are discharges of epileptiform activity and patterns of epileptic seizure. In addition, high-amplitude (more than 100-150 μV) flares of alpha, delta, and theta activity are characteristic, but they can not by themselves be considered evidence of the presence of epilepsy and are evaluated in the context of the clinical picture. In addition to the diagnosis of epilepsy, the EEG plays an important role in determining the form of epileptic disease, on which the prognosis and drug choice depends. EEG allows you to select the dose of the drug to assess the reduction of epileptiform activity and to predict the side effects of the appearance of additional pathological activity.

To detect epileptiform activity on EEG, light rhythmic stimulation (mainly with photogenic seizures), hyperventilation or other effects is used, based on information on seizure triggers factors. Long-term registration, especially during sleep, contributes to the identification of epileptiform discharges and epileptic seizure patterns. Provocation of epileptiform discharges to the EEG or the fit itself is facilitated by sleep deprivation. Epileptiform activity confirms the diagnosis of epilepsy, but it is possible in other conditions, at the same time, some patients with epilepsy can not register it.

[1], [2], [3], [4]

Long-term registration of the electroencephalogram and EEG-video monitoring

Like epileptic seizures, epileptiform activity on the EEG is not constantly recorded. In some forms of epileptic disorders, it is observed only during sleep, sometimes provoked by certain life situations or forms of activity of the patient. Therefore, the reliability of the diagnosis of epilepsy directly depends on the possibility of a long-term registration of the EEG under conditions of sufficient free behavior of the subject. For this purpose, special portable systems of long-term (12-24 hours or more) EEG recordings have been developed in conditions close to normal life activity. The registration system consists of an elastic cap with built-in electrodes of a special design allowing long-term reception of qualitative EEG leads. The withdrawn electrical activity of the brain is amplified, digitized and recorded on flash cards by a recorder the size of a cigarette case placed in a comfortable bag on the patient. The patient can perform ordinary household activities. Upon completion of the recording, information from the flash card in the laboratory is transferred to the computer system for recording, viewing, analyzing, storing and printing electroencephalographic data and processed as a normal EEG. The most reliable information is provided by EEG-video monitoring - simultaneous registration of EEG and video recording of the patient during an attack. The use of these methods is required in the diagnosis of epilepsy, when the routine EEG does not reveal epileptiform activity, as well as when determining the form of epilepsy and the type of epileptic seizure, for the differential diagnosis of epileptic and non-epileptic seizures, the clarification of surgical treatment goals, the diagnosis of epileptic non-paroxysmal disorders associated with epileptiform activity in sleep, control of the correctness of the choice and dose of the drug, side effects of therapy, reliability of remission.

Characteristics of the electroencephalogram in the most common forms of epilepsy and epileptic syndromes

• Benign epilepsy of childhood with centro-temporal adhesions (benign Rolandic epilepsy).
  • Outside the seizure: focal adhesions, acute waves and / or spike-slow wave complexes in one hemisphere (40-50%) or in two with one-sided predominance in the central and mid-mean leads, forming antiphase over the Rolandic and temporal region. Sometimes epileptiform activity during wakefulness is absent, but appears during sleep.
  • During an attack: a focal epileptic discharge in the central and mid-lead leads in the form of high-amplitude spikes and sharp waves, combined with slow waves, with possible spread beyond the initial localization.
• Benign occipital epilepsy of childhood with early onset (Panayotopulos form).
  • Outside the attack: 90% of patients observe mainly multifocal high- or low-amplitude complexes, an acute-slow wave, often bilateral-synchronous generalized discharges. In two thirds of cases, occipital adhesions are observed, in a third of cases - extraoccipital. Complexes arise in series when closing eyes. Mark the blocking of epileptiform activity by opening the eyes. Epileptiform activity on the EEG and sometimes seizures are provoked by photostimulation.
  • During an attack: an epileptic discharge in the form of high-amplitude spikes and sharp waves combined with slow waves, in one or both occipital and occipital leads, usually with propagation beyond initial localization.
• Idiopathic generalized epilepsy. Patterns of EEG, characteristic for children and adolescent idiopathic epilepsy with absences, and also for idiopathic juvenile myoclonic epilepsy. EEG characteristics in the primary generalized idiopathic epilepsy with generalized tonic-clonic seizures are as follows.
  • Outside the seizure: sometimes within normal limits, but usually with moderate or pronounced changes with delta, theta waves, flares of bilateral-synchronous or asymmetric complexes, a spike-slow wave, spikes, sharp waves.
  • During the attack: a generalized discharge in the form of a rhythmic activity of 10 Hz, gradually increasing in amplitude and decreasing in frequency in the clonic phase, sharp waves of 8-16 Hz, spike-slow wave complexes and a polyspike-slow wave, groups of high-amplitude delta and theta- waves, irregular, asymmetric, in the tonic phase, delta- and theta-activity, sometimes ending with periods of lack of activity or low-amplitude slow activity.
• Symptomatic focal epilepsies: characteristic epileptiform focal discharges are observed less regularly than with idiopathic ones. Even seizures can manifest not typical epileptiform activity, but bursts of slow waves or even desynchronization and seizure-related EEG associated with a seizure.
  • With limbic (hippocampal) temporal epilepsies during the interictal period, changes may be absent. Usually, focal complexes are observed in the acute-slow wave in the temporal leads, sometimes bilateral-synchronous with one-sided amplitude dominance. During the attack, flashes of high-amplitude rhythmic "steep" slow waves, or sharp waves, or complexes, an acute-slow wave in the temporal leads with spreading to the frontal and posterior. At the beginning (sometimes during the seizure) one-sided flattening of the EEG can be observed. With lateral-temporal epilepsies with auditory and less often visual illusions, hallucinations and sleep-like conditions, speech and orientation disorders, epileptiform activity on the EEG is observed more often. Disorders are localized in the mid- and posterior-temporal leads.
  • With the absence of convulsive temporal attacks proceeding in the type of automatism, a picture of an epileptic discharge in the form of a rhythmic primary or secondary generalized high-amplitude delta activity without acute phenomena is possible, and in rare cases in the form of diffuse desynchronization manifested by a polymorphic activity of less than 25 microvolts.
  • EEG in the case of frontal-lobe epilepsies in the inter-admission period in two-thirds of cases of focal pathology does not reveal. In the presence of epileptiform fluctuations, they are recorded in the frontal leads from one or both sides, bilaterally synchronous spike-slow wave complexes are observed, often with a lateral predominance in the frontal areas. During the seizure, bilateral-synchronous discharges can be observed spike-slow wave or high-amplitude regular delta or theta waves, mainly in the frontal and / or temporal leads, sometimes sudden diffuse desynchronization. In orbitofrontal foci, three-dimensional localization reveals the corresponding location of the sources of the initial acute waves of the epileptic seizure pattern.
• Epileptic encephalopathy. The proposal of the Commission on the terminology and classification of the International Antiepileptic League introduced a new diagnostic heading, which includes a wide range of severe epileptic disorders, epileptic encephalopathies. These are permanent impairments of brain functions caused by epileptic discharges, manifested on the EEG as epileptiform activity, and clinically by a variety of long-lasting mental, behavioral, neuropsychological and neurological disorders. These include the West's infantile spasm syndrome, Lennox-Gastaut syndrome, other severe "catastrophic" infant syndromes, and a wide range of mental and behavioral disorders that often occur without epileptic seizures. Diagnosis of epileptic encephalopathy is possible only with the help of EEG, because in the absence of seizures only it can establish the epileptic nature of the disease, and in the presence of seizures, it is to the epileptic encephalopathy that the disease is attributed. Below are the data on changes in the EEG in the main forms of epileptic encephalopathy.
• The syndrome of infantile spasms of West.
  • Outside the attack: gypsarhythm, that is, continuous generalized high-amplitude slow activity and acute waves, adhesions, spike-slow wave complexes. There may be local pathological changes or persistent asymmetry of activity.
  • During the attack: the fulminant initial phase of the spasm corresponds to generalized adhesions and acute waves, tonic convulsions are generalized adhesions that increase in amplitude toward the end of the seizure (beta activity). Sometimes the seizure is manifested by the suddenly arising and ceasing desynchronization (a decrease in the amplitude) of the current epileptiform high-amplitude activity.
• The Lennox-Gastaut syndrome.
  • Outside the attack: continuous generalized high-amplitude slow and hypersynchronous activity with acute waves, spike-slow wave complexes (200-600 μV), focal and multifocal disorders corresponding to the pattern of gypsarhythmia.
  • During the attack: generalized spikes and sharp waves, complexes spike-slow wave. With myoclonic-astatic seizures - complexes spike-slow wave. Sometimes they notice desynchronization against the background of high-amplitude activity. During tonic seizures, generalized high-amplitude (> 50 microvolts) acute beta activity.
• Early infantile epileptic encephalopathy with the "flash-suppression" pattern on the EEG (Otahar syndrome).
  • Outside the attack: generalized activity "flash-suppression" - 3-10-second periods of high-amplitude 9-, 5-activity with irregular asymmetric complexes a polyspike-slow wave, an acute-slow wave of 1-3 Hz interrupted by periods of low-amplitude (<40 μV ) polymorphic activity, or gipsaritmia - generalized 8- and 9-activity with spikes, acute waves, spike-slow wave complexes, polyspike-slow wave, acute-slow wave amplitude of more than 200 microvolts.
  • During the attack: an increase in the amplitude and number of spikes, acute waves, spike-slow wave complexes, a polyspike-slow wave, an acute-slow wave with an amplitude of more than 300 microvolts or a flattening of the background record.
• Epileptic encephalopathy, manifested mainly by behavioral, mental and cognitive impairments. These forms include the epileptic aphasia of Landau-Kleffner, epilepsy with constant complexes, spike-slow wave in slow wave sleep, frontal-lobar epileptic syndrome, acquired epileptic syndrome of the development of the right hemisphere, and others. Their main feature and one of the main criteria of the diagnosis is coarse epileptiform activity, corresponding in type and localization to the nature of the impaired brain function. With common violations of development of the type of autism, bilateral-synchronous discharges characteristic of absences can be observed, with aphasia - discharges in the temporal leads, etc.

[5], [6], [7]