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Other conditions may be confused with epilepsy, such as syncope, stroke, and certain psychological conditions. The first step in evaluation is an accurate diagnosis. Once epilepsy is diagnosed, identifying the cause and determining treatment are the next priorities.
Several tests are used in the evaluation of epilepsy.
The EEG is a recording of a patient's brain-wave activity. In epilepsy, the electrical activity of the brain is disturbed, and this can often be detected on the EEG. The pattern of the brain-wave activity may help in diagnosing seizure type. In patients with partial epilepsy, the EEG may also help to localize the area of seizure onset.
During an EEG, a series of 32 electrodes are placed on the patient's scalp to record the electrical activity of the brain.
The EEG appointment takes one to two hours. The yield of the EEG in epilepsy is higher if a sleep recording is obtained. Therefore, patients are encouraged to limit their sleep the night before the EEG to four to six hours, so that they are more likely to sleep during the study. Sedation services overseen by trained nursing staff are available for pediatric patients.
Inpatient video-EEG monitoring is used to localize seizure onset in patients undergoing evaluation for epilepsy surgery. It is also used to confirm epilepsy when the diagnosis is uncertain.
More than 600 adult and pediatric patients are evaluated in the adult and pediatric monitoring units at Mayo Clinic each year. The average hospital stay in the EEG monitoring unit ranges from four to seven days. The EEG monitoring units are open 24 hours a day, seven days a week. The monitoring units are hospital-based, so that medication can be reduced if necessary to record a seizure.
Magnetic resonance imaging (MRI) allows detailed imaging of the brain. MRI has greatly enhanced the ability to detect certain lesions in the brain that cause seizures. MRI is an important tool in diagnosing the causes of epilepsy, and in evaluating potential candidates for surgery. MRI scanning, using special techniques, may detect very subtle asymmetries in the brain that may help determine on which side of the brain the seizures start.
Research at Mayo Clinic has resulted in the development of several techniques to evaluate patients with epilepsy. Abnormalities can be subtle, and may go undetected unless these techniques are used. A typical MRI takes approximately 45 minutes.
PET (positron emission tomography) gives an image of the activity of different parts of the brain. In a PET scan, a safely dosed radioactive "tracer" is injected into the vein, and the scan is performed afterwards. PET is potentially helpful in patients with partial seizures in whom the MRI does not show an abnormality causing the problem.
Ictal SPECT (single photon emission computed tomography) is an imaging technology which is used to assist in seizure localization. It is primarily used in patients being evaluated for epilepsy surgery when the area of seizure onset is not clear on MRI or EEG.
In this test, two scans are performed. In the first, a radioactive "tracer" is injected as soon as possible after a seizure begins. A scan is performed soon afterwards. The second scan is performed 24 hours later. The tracer is injected while the patient is not having a seizure, and a second scan performed. A computer compares the two images and highlights the area of greatest activity during the seizure. This image is placed on the patient's MRI. The resulting image is known as "SISCOM" (subtraction ictal SPECT co-registered to MRI). This technique was developed at Mayo Clinic, and has helped to improve the outcomes in patients undergoing epilepsy surgery.
In neuropsychological testing, a patient's memory and cognition are measured. The most familiar example of neuropsychological testing is the IQ test. Neuropsychological testing can sometimes help identify areas of the brain that are not functioning normally, which may provide a clue as to the area of seizure onset. For example, impaired memory for word lists may indicate abnormal left temporal function.
Because one risk of epilepsy surgery relates to the effects of surgery on memory and cognition, baseline neuropsychological testing is an important component in presurgical evaluation. Neuropsychological testing for pre-epilepsy surgery evaluation takes four hours to complete.
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