Diagnosing Seizures and Epilepsy
Seizures are unpredictable. When a person has a seizure, it is usually not in a doctor’s office or other medical setting where health care providers can observe what is happening, so diagnosing seizures is a challenge. Accurate diagnosis depends on taking a careful medical history and using brain imaging and other tests to assess abnormal patterns of electrical activity in the brain.
What You Need to Know
- Proper diagnosis of seizures and epilepsy is essential for effective treatment. Diagnostic tests can help determine if and where a lesion in the brain is causing seizures.
- The doctor will begin by taking a history —asking the person or parent questions about general health, and the seizures and their pattern of occurrence.
- Diagnostic imaging procedures such as brain MRI, MRS, PET, and fMRI help the doctor ascertain characteristics of the seizures such as their place of origin (focus or foci) in the brain.
- More assessments by neuropsychologists, speech and cognitive experts and others can help complete the clinical picture of a person’s seizures and indicate what course of treatment may be most beneficial.
Routine EEG: Monitoring of electrical signals in the brain with electrodes (sensors) attached to the scalp is usually first performed in a specialized outpatient clinic. These studies are interpreted, or “read,” by a trained neurologist. Clinicians can find evidence of abnormal electrical activity in the brain and figure out the type or types of seizures a patient is having, as well as the origin(s), by measuring brain waves over minutes to a couple of hours.
Prolonged EEGs: If a routine EEG is normal, diagnosing seizures may require a stay in an epilepsy monitoring unit for continuous EEG monitoring with video over several days. Prolonged video-EEG monitoring uses a video camera to capture onset and characteristics of seizures simultaneously with an EEG.
Some seizures and epilepsies are due to irregularities within the brain tissue, such as scars, tumors or other lesions that can show up on radiologic imaging. Some of these issues can be treated with epilepsy surgery. Radiologic tests include:
Magnetic Resonance Imaging (MRI)
A brain MRI allows a physician to clearly see a patient’s internal body structures, including brain tissue, using magnetic fields and radio waves.
By revealing details of the brain’s structure in cross-sectional images called “cuts,” MRI can help the doctor locate possible seizure-producing areas in or next to the regions of structural change (called a seizure focus in patients with focal epilepsy or foci in patients with multifocal epilepsy).
Diagnostic protocols for epilepsy may involve a 3-D portion and special coronal cuts so the epilepsy specialist can evaluate the temporal lobes for signs of mesial temporal sclerosis or malformation of a part of the brain called the hippocampus.
A brain MRI may not be necessary or indicated in patients with generalized epilepsy (seizures coming from the entire brain at once rather than focal or multifocal areas).
Functional magnetic resonance imaging (fMRI) of the brain can help locate areas where speech, memory, movement or other functions take place. Doctors understand the general brain areas responsible for these activities, but fMRI can help pinpoint them more precisely.
During fMRI of the brain, the technologist will ask the patient to perform a specific task, such as naming objects, which illuminates active areas of the brain. This helps doctors focus on specific functional centers that may be affected by seizure disorders.
Positron Emission Tomography (PET)
A brain scan called an interictal fluorodeoxyglucose (FDG) PET scan can show changes in brain metabolism and chemistry, which is valuable in evaluating patients with many different conditions affecting the brain, especially epilepsy.
This is a nuclear medicine procedure. The patient wears a plastic mask that helps with positioning in the scanner machine. A technologist injects a small amount of radioactive material into a vein in the patient’s arm while, at the same time, taking a blood sample from the other arm. As the material moves through the brain, the scanner machine reveals and records changes.
Single Photon Emission Computed Tomography (SPECT)
Also called “ictal SPECT”, this procedure can detect areas of the brain with changes in cell metabolism, blood flow, or transmissions between brain cells during a seizure. These areas of altered activity can indicate seizure-causing conditions in a particular patient.
The test takes place in a monitoring unit where the doctors and the patient wait for a seizure to occur. The first part of the test occurs during a seizure (ictal), and the second is after the seizure (interictal); the doctors then compare these two studies. During each of the two stages, a health professional injects an imaging agent and the patient is transported to a specialized scanner that can visualize blood flow in the brain.
Physicians use intracranial monitoring technology to observe the characteristics of a patient’s seizures and correlate these findings with the electroencephalogram, or EEG. The tests can include the following:
Depth electrodes: These are small, multi-contact probes that are inserted through small holes made in the skull and the coverings of the brain.
Strip and grid electrodes: These small platinum disks are set in a sheet of plastic and inserted underneath the covering of the brain called the dura.
Depth, strip and grid electrodes record brain wave activity in between and during seizures for planning epilepsy surgery.
Other Epilepsy Tests
When epilepsy surgery is indicated to address seizures, this two-part test is part of a patient’s pre-surgical work-up. The test can predict the impact of surgery on language and memory function. Information from the Wada test helps determine the type of surgery that will best treat seizures while preserving areas of the brain associated with speech, memory and thinking functions.
Some people with epilepsy suffer from memory problems or other cognitive difficulties, such as trouble coming up with the correct word to use in a conversation. These problems may result from repeated seizures, medications, or a brain disease that is causing the seizures.
A quantitative assessment can provide insight into the severity and indicate the location of lesions that are causing the seizures. Neuropsychological assessments can gauge a patient's cognitive (thinking) abilities as they relate to the function of different brain structures. For example, impaired memory may indicate an abnormality in the function of parts of the brain called the temporal lobe and the frontal lobe.