Epilepsy Talk

Beyond EEGs…Diagnostic Tools for Epilepsy | September 13, 2010

How many of us have heard: “Your EEG is normal. You’re fine..” (“It’s all in your head?”)

I know of people who have had 5 EEGs, only to be properly diagnosed when they finally had Video EEG Monitoring. So if someone is trying to pass you off or is ignoring your symptoms, perhaps you should become a little more familiar with your diagnostic options…

EEG (Electroencephalogram) – is a non-invasive test which detects and records electrical impulses on the surface of the brain. These impulses are transmitted from small metal discs, placed on the person’s scalp, through wires which are connected to an electroencephalograph. This instrument is used to register the activity and record it on graph paper or on a computer screen. It is a safe and painless procedure which will not affect you in any way. An EEG is used by a neurologist to determine whether there are any irregular electrical activities occurring in the brain which may produce seizures. It can help identify the location, severity, and type of seizure disorder. An abnormal EEG does not diagnose epilepsy nor does a normal EEG reading exclude it.

Video EEG Monitoring – allows prolonged simultaneous recording of the patient’s behavior and the EEG. Seeing EEG and video data at the same time, permits precise correlation between seizure activity in the brain and the patient’s behavior during seizures. Video-EEG can be vital in the diagnosis of epilepsy and epileptic seizures. It allows the doctor to determine: Whether events with unusual features are epileptic seizures, the type of epileptic seizure, and the region of the brain from which the seizures arise.

Continuous Video EEG Monitoring – studies the brain waves over time. This can be accomplished through continuous Video EEG Monitoring, where a patient stays in a special unit for at least 24 hours. Antiepileptic medication is stopped for the duration of this test, since the objective is for seizures to occur so the abnormal brain waves they produce can be recorded.

A video camera connected to the EEG provides constant monitoring, enabling the medical team to pinpoint the area where a seizure occurs and track the patient’s physiological response to the seizure. Continuous monitoring can also help distinguish between epilepsy and other conditions. It can characterize the seizure type for more precise medication adjustments and locate the originating area of seizures within the brain, prior to surgery.

AEEG (Ambulatory Electroencephalography) – is a relatively recent technology that allows a prolonged EEG recording in the home setting. Its ability to record continuously for up to 72 hours increases the recording of an ictal event or interictal discharges. An AEEG is a less expensive alternative to in-patient monitoring, with costs that are 51-65 percent lower than a 24 hour inpatient admission for Video-EEG monitoring.

CAT Scan (Computerized Axial Tomography) or CT (Computed Tomography) – is an imaging technique that is a safe and non-invasive, using low radiation X-rays to create a computer-generated, three-dimensional image of the brain. It provides detailed information about the structure of the brain by using a series of X-ray beams passing through the head to create cross-sectional images of the brain. These may reveal abnormalities (blood clots, cysts, tumors, scar tissue, etc.) in the skull or brain which may be related to seizures. It allows physicians to examine the brain, section by section, as the test is being conducted. The CAT scan helps to point to where a person’s seizures originate.

MRI (Magnetic Resonance Imaging) – is a safe and non-invasive scanning technique that uses a magnetic field, radio waves and a computer to produce two or three-dimensional images of the brain. This detailed picture of brain structures helps physicians locate possible causes of seizures and identify areas that may generate seizures. No X-rays or radioactive materials are used, therefore this procedure is not known to be harmful. An MRI offers doctors the best chance of finding the source of seizures. Because seizures can arise from scar tissue in the brain, an MRI can show scar tissue and allow doctors to determine the nature of it. The images produced from the MRI are extremely precise. The information provided by MRI is valuable in the diagnosis and treatment of individuals with epilepsy and in determining whether surgery would be beneficial.

Functional MRI – takes images in “real-time” sequence and faster than the traditional MRI. By providing information about active brain tissue function and blood delivery, it is more precise and is often used before surgery to create a map of the brain and indicate where language, motor and sensory areas are located. During the scan, the patient is asked to perform certain tasks, such as tapping fingers or repeating a list of words. From the image, the neurological team can locate the exact seizure area of the brain.

MEG (Magnetoencephalography) – this technique has been available for several decades, but it is only recently that scanners involving the whole head have been available. The brain scan is based on natural magnetic fields. Detectors are placed on the skin near the head and then magnetic waves are used to measure brain activity. MEG is most often used to find the precise point in the brain where the seizures start by detecting the magnetic signals generated by neurons. With these signals, doctors can monitor brain activity at different points in the brain over time, revealing different brain functions. While MEG is similar in concept to EEG, it does not require electrodes and it can detect signals from deeper in the brain than an EEG.

Doctors also are experimenting with brain scans called MRS (Magnetic Resonance Spectroscopy) – that can detect abnormalities in the brain’s biochemical processes, and with Infrared Spectroscopy, a technique that can detect oxygen levels in brain tissue.

PET (Positron Emission Tomography) – is a scanning technique which detects chemical and physiological changes related to metabolism. It produces 3-dimensional images of blood flow, chemical reactions and muscular activity in the body as they occur. It measures the metabolism of glucose, oxygen or other substances in the brain, allowing the neurologist to study brain functions. By measuring areas of blood flow and metabolism, the PET scan is used to locate the site from which a seizure originates. A small amount of radioactive substance is injected into the body. When this substance reaches the brain, a computer uses the recorded signals to create images of specific brain functions. A functional image of brain activity is important because these changes are often present before structural changes occur in tissues. The information provided by the PET scan is valuable in both the diagnosis of seizure type and the evaluation of a potential candidate for surgery. PET images are capable of detecting pathological changes long before they would be made evident by other scanning techniques.

SPECT (Single Photon Emission Computed Tomography) – is primarily used to view how blood flows through arteries and veins in the brain. Tests have shown that it might be more sensitive to brain injury than either MRI or CT scanning because it can detect reduced blood flow to injured sites. The test can track cerebral blood flow and detect alterations in brain metabolism between and during seizures. SPECT scanning is also useful for presurgical evaluation of medically uncontrolled seizures.

The Wada Test (Intracateroid Sodium Ambobarbital Test) – helps to identify the areas of a person’s brain that control speech and memory functions. During this pre-operative procedure, an angiogram of the brain is taken (an X-ray of the brain’s blood vessels). A drug is then injected into the patient that anesthetizes one side of the brain. The patient is asked to respond to a series of memory and speech-related tests. From this test, the neurosurgical team can determine where the areas of the brain that control speech and memory are located, and avoid those areas during surgery.

Blood Tests – often blood samples are taken for testing, particularly when a child is involved. These blood samples are screened for metabolic or genetic disorders that may be associated with the seizures. They also may be used to check for underlying problems such as infections, lead poisoning, anemia, and diabetes that may be causing or triggering the seizures.

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Resources:

http://www.ninds.nih.gov/disorders/epilepsy/detail_epilepsy.htm#152763109

http://www.netdoctor.co.uk/diseases/facts/epilepsy.htm

http://www.med.nyu.edu/cec/diagnosing/diagnostic/eeg_video_monitoring.html

http://www.everydayhealth.com/epilepsy/neuroimaging.aspx

http://www.nyuepilepsy.org/cec/diagnosing/diagnostic/meg.html

http://www.epilepsyyork.org/diagnosing%20epilepsy.htm

http://www.theuniversityhospital.com/epilepsy/html/diagnosisandtreatment/diagnostictests.htm

http://www.mayfieldclinic.com/PE-SPECT.htm

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