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What can Cause an Abnormal EEG?

By T. Carrier
Updated: Mar 03, 2024

Many individuals undergo an electroencephalogram, or EEG, every year. This medical scan helps medical professionals determine if a patient’s brain is functioning normally. An abnormal EEG result can result from a number of causes, including epilepsy and seizures, brain tumors, head injuries, and degenerative disorders.

EEGs produce results by measuring the electrical impulses brains produce. These signals aid brain cells in communication. When they are responding in an erratic fashion, the abnormal EEG can indicate a possible brain dysfunction.

Technicians measure brain signals by placing small metal discs known as electrodes across the head. Electrodes are attached to an EEG machine, and this machine reads the impulses and translates them into patterns viewable on a computer or other electronic screen. Trained technicians can then detect any strange features in these patterns.

A physician will often order an EEG if he or she suspects a patient has a certain condition. For example, if an individual presents with the typical symptoms of a seizure disorder like epilepsy, an EEG can confirm the diagnosis. Severe shaking, body slumping, and temporary loss of consciousness are primary features of most seizures. Such suspected brain ailments represent the bulk of abnormal EEG findings.

Another brain dysfunction commonly discovered by EEG tests is a brain tumor. A mass can wreak havoc on the brain’s efficiency. Tumors may block the flow of blood to the brain — known as cerebral infarction — and facilitate subsequent death of brain tissue. Swelling of brain tissue can also occur, as can bleeding.

Any of these issues can hinder the brain’s thinking capacity and its related functions like memory and attention. These alterations can then manifest in the patterns outputted by an EEG machine. In the case of a cerebral infarction or encephalitis — brain swelling — these conditions may generate in the absence of a tumor. Severe migraines or a weakened blood vessel — known as a brain aneurysm — can cause similar issues.

Disorders that worsen over time, or degenerative disorders, can also be effectively discovered by an abnormal EEG. Technicians look for the frequency of electrical brain activity as well as patterns. In a healthy individual, brain activity increases when a person is conscious and fully functioning. Slower output of brain waves is among the first indicators of a degenerative brain disorder like Alzheimer’s disease. In addition, some avenues of research suggest EEGs may be useful in predicting if an individual is susceptible to progressive mental disorders like schizophrenia or depression.

In addition to detecting a potential disorder, an abnormal EEG can also provide insight into the extent of an already-known brain condition. When an individual suffers a brain injury, the severity of the damage and the location of the injury are vital factors for treatment. EEG results may pinpoint both of these issues. In particular, the amount of brain activity is directly related to how well a person will think, reason, and function in everyday activities. Therefore, an EEG reading can help predict a brain injury patient’s recovery period.

On occasion, altered brain activity can appear in a condition that is not primarily brain-related. Any major changes in the body’s overall chemistry can impact the brain. Infections are one frequent culprit of such changes, as is prolonged drug or alcohol abuse. Sleep disorders and resulting lack of sleep can adversely affect the brain as well.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
By anon1003114 — On May 04, 2020

Epilepsy runs in my family. With a genetic "oomph", seizure activity that can be induced in almost anyone, became personal. Although four generations have been diagnosed with it, epilepsy is as mysterious as ever. The majority of us have been "controlled" with medicine. Only one of us lived his life dictated by seizure activity. In our case, I would like to see EEGs done on pre-adolescents in our family, to get treated sooner. However, 'neuro' people think that's not productive.

By Ahmerus — On Jan 31, 2014

Very true Jewellian. Medical Science has come a long way. An abnormal EEG in children allows a physician to formulate a treatment process; that alone is priceless. However, I would add that the brain is still a mystery. There is so much about its functionality that we do not understand, as in the case of Alzheimer's disease. But, medical innovations like the EEG are getting us there.

By Jewellian — On Jan 30, 2014

It is amazing what medical science has accomplished, through innovation and technology. Electroencephalography and the results gathered from the EEG were unimaginable a few years ago. Doctor's could only guess at what was going on within the brain and brain maladies went untreated. People just suffered and died. There was no treatment, no cures, because know one knew how to treat the abnormality. The brain was a complete mystery.

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