A Diagnostic Application of EEG Tests

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A Diagnostic Application of EEG Tests

Typical and Atypical Absence Seizures: A Diagnostic Application of

EEG testWhen you think of a seizure, you probably picture a tonic-clonic seizure, in which the person stiffens and convulses. However, this is not the only kind of seizure. Absence seizures are just as problematic, but far more subtle. They often go unnoticed, especially in children, and can even be mistaken for daydreaming. There are two main types of absence seizures: typical absence seizures and atypical absence seizures. The most reliable way to distinguish between these two is to look at an electroencephalogram (EEG) reading. Typical absence seizures are associated with telltale brainwave abnormalities visible on an EEG readout.

What Happens in an Absence Seizure?

Absence seizures, also called petit mal seizures, are distinguished by brief “staring spells” that are not followed by a period of confusion or fatigue. They are very brief, often lasting only 30 seconds, and the person regains alertness immediately afterward. A person with absence seizures will periodically fall into these staring spells, during which they simply “stare off into space.” Because absence seizures are so brief and quiet, they can easily be mistaken for normal daydreaming. However, unlike a daydreamer, someone who is having an absence seizure is not conscious and does not remember the event afterward.

Typical and atypical absence seizures present with very similar symptoms, although there are a few differences. In a typical absence seizure, an individual will go into a “staring spell” for around 10 to 30 seconds, during which time they are unresponsive. In a complex absence seizure, automatisms, or repetitive motions, such as blinking or chewing, accompany the staring spell. The person then snaps back to normal with no memory of the time during which they had the seizure. Sometimes, the person with absence seizures may not be aware that they are even having them. An atypical absence seizure usually lasts a bit longer; often several minutes, and can begin more slowly. A person with an atypical absence seizure is also more likely to fall or slump over, and to feel drowsy and confused after the event.

Using EEG Testing to Diagnose Absence Seizures

Typical and atypical absence seizures can be distinguished from one another by looking at a person’s EEG when they are having a seizure. Typical absence seizures are associated with a telltale EEG pattern, consisting of 3-4 Hz spike-and-slow-wave complexes. These patterns reflect abnormal firing of neurons. Spike and wave patterns in typical absence seizures are very regular, whereas those in atypical absence seizures are slower and more variable. The EEG during a typical absence seizure is easily recognizable to a trained neurologist.

Electroencephalogram (EEG) testing is the most quantitative and reliable way to determine for sure if someone with staring spells has typical or atypical absence seizures. The differences in the spike-and-wave patterns are quite distinctive and allow physicians to determine which form of absence seizure someone has. This is important, because typical and atypical absence seizures differ in their underlying causes and require different treatment protocols. Using EEG testing to assess the nature of absence seizures is an important tool for neurologists and other healthcare professionals to determine the best course of treatment for a patient.


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