Electroencephalogram (EEG)

Yumnam Ranbir Singh *

Person wearing electrodes for EEG ; EEG with 32 elektrodes :: Pix - wikipedia/Aschoeke

An electroencephalogram (EEG) is a test that detects electrical activity in the brain, using small flat metal discs (electrodes) attached to the scalp. The brain cells communicate via electrical impulses and are active all the time, even when one is asleep. This activity shows up as wavy lines on an EEG recording.

An EEG is one of the important diagnostic tests for epilepsy. An EEG may also be helpful in diagnosing other brain disorders.

WHY IT IS DONE?

An EEG can determine changes in the brain activity that may be useful in diagnosing brain disorders, especially epilepsy. An EEG cannot measure intelligence or detect mental illness. An EEG may be done to:
o Diagnose epilepsy and see what type of seizures are occurring. EEG is the most useful and important test in confirming a diagnosis of epilepsy.
o Diagnose brain dysfunction that may have a variety of problems (encephalopathy).
o Diagnose stroke and inflammation of the brain (encephalitis).
o Check for problems with loss of consciousness or dementia.
o Help find out a person’s chance of recovery after a change in consciousness.
o Find out if a person who is in coma is brain-dead.
o Study sleep disorders, such as narcolepsy.

PREPARATIONS REQUIRED

The hair needs to be washed before the test. Oils, sprays, conditioners or gels should not be used on the hair. If one is taking any medication, the doctor may ask to stop some of them. Certain drugs can affect the brain’s normal electrical activity and cause abnormal test results.

Food or drinks containing caffeine have to be stopped 12 hours before the test. One may need to sleep during the test. In this case, one may be asked to sleep less the night before the test to induce sleep.

HOW IS IT PERFORMED?

Routine EEG recordings usually take 20-40 minutes, although a typical appointment may last about an hour including some preparation time at the beginning and some time at the end. The EEG procedure is painless and one should feel comfortable throughout.

The skin on the scalp is cleaned and many electrodes are placed in specific areas, measured out in correct locations.

The electrodes would be connected to an EEG machine by thin leads. The machine records the brain wave activity for later analysis. Afterwards, the electrodes would be removed and the scalp cleaned. After the procedure is over, the recordings will be analysed and used for the purpose of diagnosis and treatment.

HOW DOES IT FEEL?

There is no pain with an EEG. If paste is used to hold the electrodes, some of it can remain in the hair after the test and one has to wash the hair clean afterwards.

One may be asked to breathe rapidly, so there may be some light-headedness or slight soreness in the fingers. The reaction is normal and will go away after some time after breathing normally again.

RISKS

An EEG is a very safe test. The electrical activity of the brain is recorded but at no time is any electrical current put into the body.

If one has a seizure disorder such as epilepsy, a seizure may be triggered by the flashing lights or by hyperventilation. If this occurs, the technologist is trained to take care of the patient in the event of seizure happening.

WHAT AFFECTS THE TEST?

The results may be affected by certain factors like:
o Moving too much.
o Not eating before the test.
o Certain medications.
o Drinking coffee, tea or soda that contains caffeine before the test.
o Being unconscious from severe drug poisoning or a very low body temperature.
o Hair that is dirty, oily, or covered with hair spray or other hair preparations which may cause problems in placing the electrodes.

AFTER THE PROCEDURE

After the test, the technician will remove the electrodes. The patient will be instructed when to resume any medications. The patient generally will be ready to go home immediately following the test. No recovery time is required. Because the patient may be at risk for a seizure (especially if their medication has been withheld prior to the test), they should have someone take them home safely, and they should not drive.

RESULTS

Brain electrical activity has a certain number of waves per second that are normal for different levels of alertness. For example, the brain waves are faster when one is awake, and slower in certain stages of sleep. There are also normal patterns to these waves.

An abnormal result on EEG may occur which may be due to:
o Abnormal bleeding (haemorrhage).
o An abnormal structure in the brain (such as a tumour).
o Tissue death due to a blockage in blood flow (cerebral infarction).
o Drug or alcohol abuse.
o Head injury.
o Migraines.
o Seizure problems (such as epilepsy).
o Sleep disorder (such as narcolepsy).
o Swelling of the brain (oedema).

TYPES OF EEG

o ROUTINE EEG.
o SLEEP EEG – this is carried out while one is asleep.
o AMBULATORY EEG – this is done by recording the brain activity throughout the day.
o VIDEO TELEMETRY (VIDEO EEG) – a special type of EEG that simultaneously videos the patient and records the brain wave activity.