Violations of the electroencephalogram in diseases
Last reviewed: 23.04.2024
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EEG in brain tumors
Tumors of the brain hemispheres cause the appearance of slow waves on the EEG. When middle structures are involved in local changes, bilateral-synchronous disturbances can be added. A progressive increase in the severity of changes with tumor growth is characteristic. Extracerebral benign tumors cause less severe disorders. Astrocytomas are often accompanied by epileptic seizures, and in such cases the epileptiform activity of the corresponding localization is observed. With epilepsy, the regular combination of epileptiform activity with constant theta waves and the growing in repeated focuses in the focus area is evidence in favor of neoplastic etiology.
EEG in cerebrovascular diseases
The severity of EEG disorders depends on the severity of brain damage. When cerebral vascular lesions do not lead to severe, clinically manifested cerebral ischemia, changes in the EEG may be absent or borderline with a normal character. With discirculatory disorders in the vertebrobasilar bed, desynchronization and flattening of the EEG can be observed.
In ischemic stroke in the acute stage, changes are manifested by delta and theta waves. In carotid stenosis, pathological EEG occurs in less than 50% of patients, with carotid thrombosis in 70%, and in middle cerebral artery thrombosis in 95% of patients. Persistence and severity of pathological changes on the EEG depend on the possibilities of collateral circulation and the severity of brain damage. After an acute period on the EEG, a decrease in the severity of pathological changes is observed. In some cases, in the long-term period of a stroke, the EEG normalizes even if the clinical deficit persists. With hemorrhagic insults, changes in the EEG are much more severe, persistent and widespread, which corresponds to a more severe clinical picture.
[3], [4], [5], [6], [7], [8], [9]
EEG in case of traumatic brain injury
Changes in the EEG depend on the severity and presence of local and general changes. When the brain is concussed during the loss of consciousness, generalized slow waves are observed. In the near future, rough diffuse beta waves with an amplitude of up to 50-60 μV can appear. When the brain is bruised and crushed, defective theta waves of high amplitude are observed in the lesion area. With extensive convectional lesion, a zone of lack of electrical activity can be detected. With the subdural hematoma, slow waves are observed on its side, which may have a relatively low amplitude. Sometimes the development of a hematoma is accompanied by a decrease in the amplitude of normal rhythms in the corresponding area due to the "screening" action of the blood. In favorable cases in the long-term after the injury EEG normalizes. A prognostic criterion for the development of posttraumatic epilepsy is the appearance of epileptiform activity. In some cases, in the long-term after the trauma, the diffuse flattening of the EEG develops, indicating the inferiority of the activating nonspecific brain systems.
EEG in inflammatory, autoimmune, prion diseases of the brain
When meningitis in the acute phase, severe changes are observed in the form of diffuse high-amplitude delta and theta waves, foci of epileptiform activity with periodic outbreaks of bilateral-synchronous pathological oscillations, indicative of the involvement of the median parts of the brain in the process. Persistent local pathological foci may indicate a meningoencephalitis or brain abscess.
In panencephalitis , periodic complexes are typical in the form of stereotyped generalized high-amplitude (up to 1000 μV) discharges of delta and theta waves, usually combined with short oscillation spindles in alpha or beta rhythm, as well as with sharp waves or spikes. They arise as the disease progresses from the appearance of single complexes, which soon acquire a periodic character, increasing in duration and amplitude. The frequency of their appearance gradually increases until they merge into continuous activity.
With herpes encephalitis, the complexes are observed in 60-65% of cases, mainly in severe forms of the disease with an unfavorable prognosis. In about two-thirds of cases, periodic complexes are focal, which is not the case with Van-Bogart's panencephalitis.
In Creutzfeldt-Jakob disease, usually at 12 months from the onset of the disease, there appears a continuous regular rhythmic sequence of complexes of the acute-slow wave type, occurring at a frequency of 1.5-2 Hz.
[14], [15], [16], [17], [18], [19], [20]
EEG in degenerative and dezantogenetic diseases
EEG data in combination with the clinical picture can help in differential diagnosis, in monitoring the dynamics of the process and in identifying the localization of the most severe changes. The frequency of EEG changes in patients with Parkinsonism varies, according to different data, from 3 to 40%. The most frequently observed slowing of the main rhythm, especially typical for akinetic forms.
For Alzheimer's disease are typical of slow waves in frontal leads, defined as "front bradiritmiya". It is characterized by a frequency of 1-2.5 Hz, an amplitude of less than 150 μV, polyrhythmicity, mainly in the frontal and anterolateral directions. An important feature of "anterior bradyarrhythmia" is its permanence. In 50% of patients with Alzheimer's disease and 40% with multi-infarct dementia of the EEG within the limits of the age norm.