How is Epilepsy Diagnosed?
Epilepsy Diagnosis: Tests, Scans, and Medical History
For a person to be diagnosed with epilepsy, they must have one of these:
- At least two unprovoked seizures more than 24 hours apart
- A known seizure cause that makes future seizures more likely
- A known epilepsy syndrome
An unprovoked seizure is one in which there is no cause identified aside from abnormal electrical activity in the brain. The term “unprovoked” is also sometimes used for seizures caused by a brain lesion or neurodegenerative process, because these carry a higher risk for future epileptic seizures.
To determine whether symptoms are caused by epilepsy, other potential causes of seizures must be ruled out. There are many causes of epilepsy-like symptoms that are not caused by epilepsy.
A wide variety of tests can help to rule out other causes for seizures and find out what part of the brain is seizing. With a more detailed diagnosis, better treatment choices can be made.
An EEG records the brain’s electrical activity, including any abnormalities in the brain waves. Ideally this test is performed within 24 hours of a person’s first seizure.
The EEG is a standard test to assess the abnormal electrical brain activity that causes epilepsy. But some people who have epilepsy have a normal test, and some people without epilepsy have abnormalities that show up on an EEG.
Another drawback of the EEG is that the seizures can be too deep in the brain to be detected by the electrodes that are placed on the scalp during the test.
Sometimes a videotape is made of the person during a seizure while the EEG is also reading brain waves. This test is typically done in a hospital setting, where the seizure can be monitored. A video EEG allows specialists to compare the person’s brain waves with their symptoms, sometimes giving a more complete picture of what’s going on in the brain.
Blood Tests to Rule Out Other Causes
There isn’t a blood test for epilepsy itself, but there are blood tests that can help rule out other causes of seizures.
When a person has his first seizure, the emergency department team may order a drug screen to see whether the person was exposed to recreational drugs. That’s because a number of drugs, such as cocaine and PCP (phencyclidine, or “angel dust”), can cause seizures.
Some seizure disorders are syndromes caused by known genetic mutations, so genetic testing can be helpful in diagnosing these.
Other blood tests can indicate that seizures were caused by an illness or by abnormal levels of salts or sugar in the blood, not by epilepsy.
Radiologic Tests for Epilepsy
Radiologic tests for causes or evidence of epilepsy include: (1, 2)
- Magnetic resonance imaging (MRI) can reveal structural problems with the brain that may be causing seizures, like tumors or cysts. One type, called a functional MRI (fMRI), can be used to check for abnormalities in function.
- Computed tomography (CT) is used to look for bleeding or structural abnormalities in the brain that may cause seizures.
- Positron emission tomography (PET) is used to identify areas of lower metabolism in the brain, which happens after a seizure.
- Single photon emission computed tomography (SPECT) can be used to compare the brain blood flow during a seizure with the brain blood flow between seizures.
A person’s medical history can provide a lot of insight into the kind of seizures he or she is having and whether they're due to epilepsy. Some information that it is useful in making a diagnosis includes:
- Symptoms and duration of the seizures. If the person doesn’t remember the seizures or can’t recount them, a witness or caregiver account with as much detail as possible is helpful.
- Any information about family history of seizures
- A history of any other medical or psychological problems and medications taken
Seizures in Children
Infants and children have different EEG patterns from adults, and their response to antiseizure drugs is also different. The brain of a newborn infant or young infant is more prone to seizures for a variety of reasons, but an infant’s seizures are also more prone to disappear as the child grows.
Epilepsy in Older Adults
Nearly 25 percent of new-onset seizures occur in people older than 65. Researchers think that 2 to 5 percent of older adults have epilepsy, with the major causes being cerebrovascular disease, dementia, and trauma. For all these causes, the risk of epilepsy is highest in the first two years after onset of the underlying cause. For one-third to one-half of older adults with seizures, the cause is unknown.
Video: Video EEG Monitoring for Epilepsy
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