Electroencephalogram (assessment tests)




The electroencephalogram (EEG) is a painless and non-invasive instrumental examination that allows you to analyze, monitor and record the "electrical activity of the brain.

This activity produces electrical waves which, in an adult in a state of well-being and in conditions of rest, have a frequency of 8-13 cycles per second (alpha rhythm).

In case of brain abnormalities, this rhythm is altered. Therefore, the electroencephalographic recordings allow to "identify a pathological cerebral condition, the causes of which will have to be investigated with further instrumental examinations such as CT (computerized axial tomography) or MRI (magnetic resonance) of the brain, or" examination of the fluid circulating in the brain and in the medullary canal (cerebrospinal fluid).

The electroencephalogram records the difference in electrical potential existing between pairs of electrodes positioned on the head at different areas of the brain surface (cerebral cortex).

The electrodes, placed on the skin, are connected to an amplifier which collects the electrical impulses and sends them to a recorder and to a "device capable of translating them into a graph. This recording can take place either on paper or on an external electronic device. .

The examination must be carried out in a quiet environment and away from possible interference: other electrical machinery in operation, sounds or other noises.

The electroencephalographic trace shows data concerning the function of the brain, therefore it varies according to the waking or sleeping condition and the age of the person.

For these reasons, the interpretation of the electroencephalogram is always entrusted to expert medical specialists for adults or children.

The EEG is an examination frequently performed in clinical practice, together with other complementary analyzes to guide the neurological diagnosis. In particular, the EEG is indicated in cases of alterations in consciousness or cognitive functions, in case of sudden changes in behavior, in most of the pathologies that manifest themselves with sleep disorders, and in the presence of localized (focal) neurological disorders (symptoms) which do not correspond to damage in the structure of the brain such as to be detectable with a CT scan or a brain MRI.

When to perform the EEG (indications)

When to perform the EEG (indications)

Some brain diseases, such as epilepsies, encephalitis, prion diseases, are generally associated with characteristic signs in the electroencephalogram; others, on the other hand, do not show a particular type of path.

Therefore, based on the present disorders, the electroencephalogram may be requested by the doctor to validate a diagnostic hypothesis or to deem it less likely.

The electroencephalogram (EEG) is indicated in many conditions, here are the main ones:

  • The EEG is performed mainly in the presence of a particular type of neurological symptoms, which are commonly called Seizures. Epileptic seizures are sudden phenomena and, generally, of short duration, which depend on an "altered electrical function of neurons (cells of the nervous system) due to various conditions. During an epileptic seizure, alterations in the state of consciousness, convulsions can occur ( involuntary contractions of various muscles of the body) and various other ailments.
    The causes of seizures can be:
    • structural brain damage (such as a tumor, "ischemia or" haemorrhage, vascular malformations, vasculitis, lesions caused by multiple sclerosis, or from trauma)
    • genetic diseases (many epilepsies that appear in childhood and adolescence have a genetic origin)
    • infectious diseases (such as meningitis or encephalitis)
    • metabolic alterations (such as alcohol abuse, drug or other substance intoxication, drug withdrawal)
    • diseases of the immune system
    • unknown causes
    The electroencephalogram is a very useful instrumental examination in these cases in helping the doctor to make a correct diagnosis, recommend a specific therapy or modify a therapy already in progress
  • The EEG is also indicated when gods occur disorders that could be misinterpreted as seizures, for example: cardiovascular, psychological and psychiatric disorders; some disturbances of a mainly visual type that precede the onset of headache (ie migraine aura) and involuntary movements of the muscles and limbs. In such cases, the EEG helps the physician to consider causes other than epilepsy
  • In the case of a dementia syndrome (reduction or loss of memory and other brain abilities such as spatial orientation and judgment, and behavioral changes) the EEG, along with other laboratory and instrumental tests (blood tests, brain CT and MRI) ) provides information necessary to rule out certain conditions that may be similar to dementia (such as, for example, drug intoxication or brain damage)
  • The EEG is indicated to analyze brain function in people with sleep disorders as:
    • sleep apnea syndrome (trouble breathing during sleep)
    • nocturnal epilepsy
    • dissomnia:
      • insomnia (difficulty or inability to fall asleep)
      • narcolepsy (sudden daytime sleep attacks)
      • hypersomnia (excessive daytime sleepiness)
    • parasomnia:
      • bruxism (grinding of teeth during sleep)
      • enuresis (nocturnal urinary incontinence)
      • sleepwalking (perform actions during sleep without being aware of it)
    For the diagnosis of these and other sleep diseases, in addition to performing the EEG, it is advisable to contact centers specialized in sleep medicine.
  • The EEG is mandatory in case of removal of organs for transplantation, to ascertain the donor's state of brain death

How the electroencephalogram is performed

Generally, the electroencephalogram (EEG) is performed by a neurophysiopathology technician and the results are interpreted and written in the report by a physician specialized in neurology. It is performed by placing small electrodes on the skin of the head held in place by a rubber cap.

In specific cases, such as in patients who are in an operating room or in an intensive care unit, particular electrodes such as needle-electrodes (electrodes that are inserted into the skin using a needle) or collodion electrodes (electrodes) can be used. which are temporarily glued to the skin).

According to the indications for which it is performed, the duration of the electroencephalogram can vary from 30 to 60 minutes.

How to prepare for an EEG

How to prepare for an EEG

Unless otherwise indicated, no special precautions are necessary before undergoing the electroencephalogram: you can either eat, drink or continue to take current therapies.

For better adhesion of the electrodes to the scalp, the hair should be clean and dry and the use of gel and wax should be avoided.

The doctor will cover the patient's head with a specific gel to allow for good electrical conduction during the examination.

It is advisable to carry a comb to tidy up the hair after the examination or a hat to cover the messy head (the hair may not be very clean at the end of the EEG).

Types of EEG

Types of EEG

There are several types of electroencephalogram (EEG): basic, in sleep deprivation, dynamic, in video telemetry.

Basic EEG

The basic EEG recording takes about 20 to 40 minutes.

During the exam, you are asked to remain calm and, from time to time, to open and close your eyes to evaluate the reactivity of the cerebral rhythm.

Subsequently, two activation maneuvers are performed:

  • hyperventilation, that is, you are asked to perform deep inhalations and exhalations for a few minutes
  • intermittent light stimulation, using an instrument called a stroboscope

Both maneuvers are aimed at highlighting any epileptic anomalies.

EEG in sleep deprivation

This type of examination is done while the person is sleeping. It can be used if a basic EEG does not provide enough information or to check for sleep disturbances.

In some cases, you may be asked to stay awake the night before the exam in order to fall asleep more easily when the EEG is performed. For this reason, the test is called a sleep deprivation EEG.

Dynamic EEG (Holter)

A dynamic EEG records brain activity during the day and night over a period of one or more days. The electrodes are attached to a small portable EEG recorder that can be clipped to clothing. Most normal activities can continue. daily while recording, although you should avoid getting the equipment wet.

Video telemetry

Video telemetry, also known as video-EEG, consists of filming the person recording their brain activity (with regular authorization from the person himself). Usually, video telemetry is performed over a few days during a hospital stay.

The EEG signals are transmitted to a computer. The video is also recorded by a computer on which a camera is placed. All registrations are always carried out in the presence of specialized personnel.

What happens after an EEG

What happens after an EEG

When the electroencephalogram (EEG) is done, the electrodes are removed and the scalp is cleaned. Your hair will likely be sticky and messy.

You can usually go home right after the exam and return to normal activities.

In some cases, especially if you have undergone an EEG in sleep deprivation, you may feel tired after the examination. In these cases it is advisable to be accompanied and not to drive.

Usually, EEG results are not available on the same day as the exam. The recordings, in fact, must be analyzed and sent to the specialist who, after a few days, will deliver the results.

Risks or undesirable effects of the EEG

Risks or undesirable effects of the EEG

The electroencephalogram (EEG) is painless and generally very safe. No electric shock is released into the body during the examination. The only discomfort can be represented by the hair which, at the end of the examination, will be dirty and disordered and slightly tired. For these characteristics the examination can also be performed in pregnant women.

At the end of the procedure, there may be a state of slight confusion and tingling in the lips and fingers during the hyperventilation portion of the base EEG. In addition, some people may have a slight rash on the scalp where they were applied. the electrodes.

In case of epilepsy, or in people suffering from seizures, there is a very small risk that a seizure may occur while performing the EEG. In this case people will be helped and monitored by highly qualified personnel.

In-depth link

In-depth link

NHS Choices. Electroencephalogramm (EEG) (English)

Italian Association for Cancer Research (AIRC). Electroencephalogram

San Raffaele Hospital. Electroencephalography laboratory

Fisher RS. The New Classification of Seizures by the International League Against Epilepsy 2017 [Summary]. Current Neurology and Neuroscence Report. 2017; 17: 48

Italian League against Epilepsy (LICE). Guide to epilepsies

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