What Tests are Used to Diagnose Epilepsy?

What Tests are Used to Diagnose Epilepsy?

Is there a certain type of test needed for epilepsy diagnosis?

The diagnosis of epilepsy is a clinical diagnosis. Your doctor will diagnose epilepsy based on the information from the history, physical examination, EEG, and brain imaging studies.

There are certain tests to support the diagnosis of epilepsy such as electroencephalogram (EEG) and brain imaging. EEG amplifies electrical activity in brain and records and displays them on a computer screen. In the past EEG displays were on paper. Abnormalities such as spikes, sharp and slow waves occur during seizures. In between seizures EEG may not show any abnormalities. EEGs in between seizures can be normal. Multiple repeats of EEG tests will increase the chance to catch abnormalities supporting epilepsy diagnosis. There is no blood test for epilepsy.

Imaging such as computed axial tomography of head and magnetic resonance imaging of brain provide detailed information about brain structure. They can reveal birth defects, tumor, scars, and stroke, all of which can cause epilepsy.

Why EEG? What is the purpose?

Electroencephalogram (EEG) is a test to record brain activities. It amplifies brain activities and displays them as waves. EEG machines record the brain activities through the electrodes. The electrodes are glued or pasted on the scalp. Amplifiers in the machine magnify the brain signals. The recordings are written on paper or digitized and displayed on the computer monitor. Spike and wave is a distinctive pattern and occurs in patients with epilepsy.

EEGs are to support and eventually confirm the diagnosis and also can be helpful to classify the type of epilepsy syndrome. For example typical pattern 3 Hz spike and wave is seen in patients with idiopathic generalized epilepsy. Determining the type of epilepsy is very important in choosing therapeutic options, becasue some anti-epileptics may not control certain seizures.

Before EEG test you may be asked to be sleep deprived. It is very well known that sleep deprivation is a seizure trigger. Also it will help you sleep during EEG test, which can improve chance of detecting abnormalities on EEG test.

During EEG test you may be provoked by flashing lights and hyperventilation. These provocative techniques can cause seizures in some patients. Flashing lights trigger seizures in patients with photosensitive epilepsy. Hyperventilation lowers seizure threshold and can cause seizures.

CAT Scan versus MRI? What is the difference?

CAT scan was the first Xray machine to rely on computer in brain imaging. It uses Xrays to take the picture of brain. It is very sensitive test in identifying acute changes such as bleeding in the brain or skull fractures.

On the other hand, magnetic resonance imaging (MRI) employs magnetic field to produce the image of brain. There is no risk of radiation with MRI. It is superior to CAT scan in delineating the structural abnormalities in the central nervous system suc h as scarring, inflammation, infection, stroke, and tumor. An MRI may need to be conducted in almost all patients with new ons et epilepsy.

Single Photon Emission Computed Tomography (SPECT)

SPECT is another nuclear medicine imaging study. It is used when patients are considered for epilepsy surgery. It identifies the seizure focus by detecting altered focal blood flow. Increased blood flow is seen in epileptic tissue as the seizure starts.

The drawback of this test is the patient must have had seizure few minutes prior to the testing. At the onset of seizure the patient is injected a radioactive material. SPECT tracks the uptake of this radioactive substance in the brain to identify the epileptic tissue. Like PET, SPECT is not a routine study, utilized when patients are considered for epilepsy surgery. It is performed in inpatient hospital setting.

Positron Emission Tomography (PET)

PET is a nuclear medicine imaging test that has been used to localize the area of abnormality causing seizures. It is an additional supportive study to EEG and brain MRI in localizing the seizure focus. This test is not a routine test and performed when epilepsy surgery is considered to optimize seizure control in patients with uncontrolled seizures.

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