How is epilepsy (seizure disorder) diagnosed?

The diagnosis of epilepsy is based on careful and detailed accounts of the typical seizure as described by both the patient and the witness. This clinical information is more important in the diagnosis than any one of the subsequent tests. In addition to that, an EEG (electroencephalogram) may help confirm the suspected type of epilepsy. The EEG capturing the typical seizure has the highest diagnostic sensitivity, ideally with a video- EEG. If EEG is obtained between the seizures it may be entirely normal, and in this case is considered non-diagnostic. MRI of the brain is also required most of the time and is commonly normal. In addition, MEG (magneto-encephalography) is also helpful in the diagnosis of epilepsy.

Advanced diagnostic tests for diagnosing epilepsy include:

  • In-patient monitoring: Determines the frequency and severity of seizures and verifies the seizure type and site of onset in the brain.
  • Imaging tests: Includes MRI (magnetic resonance imaging), SPECT (single-photon emission computed tomography), and PET (positron emission tomography) scans to locate the exact source of the seizures.
  • Additional tests: Including Wada and functional MRI to identify the critical areas of the brain that are close to the source of the seizures.
  • Neuropsychological tests: To assess cognitive functioning.

The results of these tests help classify each patient's seizures and determine the next step in treatment—whether additional medications or surgery—that is most likely to eliminate seizures.

Dr. Jeanne Morrison, PhD
Family Practitioner

Your physician will make a diagnosis of epilepsy based on several criteria. Probably the most important tool is a complete summary of your health history and an accurate and complete description of your seizure activity. Abnormal findings on your electroencephalogram (EEG) will also be helpful in making a diagnosis of epilepsy. Other diagnostic tools may include lab work, a computed tomography (CT) scan, magnetic resonance imaging (MRI), cerebral angiography, single-photon emission computed tomography (SPECT), magnetic resonance angiography (MRA), magnetic resonance spectroscopy (MRS), and/or positron emission tomography (PET) scan.

In order to diagnose your seizure disorder, also known as epilepsy, your doctor will consider your symptoms, review your medical history, and conduct a neurological exam. The neurological exam will allow your doctor to evaluate your intellectual functioning, motor skills, and behavior. Your doctor might also ask you to undergo further tests, such as an electroencephalogram (EEG) that measures your brain activity or an imaging scan of the brain. An EEG involves placing electrodes on your scalp that measure the patterns of your brain waves. This test is most valuable if it is performed within 24 hours of your first seizure. Imaging scans of the brain can reveal problems in the structure of the brain, and some kinds of imaging scans can also show brain activity. When diagnosing some patients, particularly children, doctors will often order a blood test to check for illnesses and disorders that could cause seizures.

Epilepsy by definition means having more than one unprovoked seizure (meaning nothing else caused it such as low blood sugar or other electrolytes, substances like alcohol, or a bleed in the brain). The diagnosis is made through a careful history (very useful to have observers other than the patient there). A diagnosis can often be confirmed with an EEG (brain wave study) or MRI of the brain, however, if these studies are normal, history trumps the studies. If there is still question around the diagnosis and episodes are occurring frequently, a concrete diagnosis can be made by elective admission for continuous video (EEG monitoring), where a patient is admitted until their episodes are recorded; this will lead to a definitive diagnosis in the great majority of patients.

Diagnosis begins with a thorough history, followed by a series of diagnostics, including blood tests, MRIs and electroencephalograms (EEGs), which record electrical activity in the brain and can often distinguish whether a seizure is actually epilepsy. The EEG can also determine which parts of the brain are being affected to help devise a treatment strategy.

Dr. Jerome Engel, MD

Anyone who has had an epileptic seizure, even if it is thought to be reactive, deserves a full neurological evaluation, which consists most importantly of a careful history, neurological examination, description of the seizure(s) and routine laboratory tests, as well as a brain-wave test (electroencephalogram – EEG), brain imaging (magnetic resonance imaging – MRI), and in the case of some syndromes, genetic screening. The first objective is to rule out a large variety of intermittent neurological, general medical, and psychiatric conditions that can mimic epilepsy (nonepileptic seizures, pseudoepilepsy). It is essential that such disorders are recognized and treated, and that the patient is not mistakenly diagnosed with epilepsy. If another disease is suspected special tests may be required. Next, it is important to look for an underlying treatable cause because if such a cause is treated and the seizures stop, the patient does not have epilepsy. Then the diagnosis of epilepsy requires either two epileptic seizures occurring more than 24 hours apart that are not reactive, or one such seizure and evidence from history, EEG, MRI or other tests of an enduring brain abnormality that makes it highly likely that more seizures will occur. When there is difficulty distinguishing between epilepsy and a condition that causes nonepileptic seizures, referral to a specialized epilepsy center is recommended for in-patient video-EEG monitoring in order to carefully evaluate the electrical and behavioral features of the habitual seizures.

To diagnose epilepsy, also called seizure disorder, a doctor will arrange some tests. One test for diagnosing epilepsy is an electroencephalogram (EEG). In an EEG, lots of small sensors are placed on the person's head. The sensors pick up the electrical activity inside the brain and turn it into waves. The doctor will read the waves and be able to tell what kind of electrical activity is going on inside the brain. People might also have a magnetic resonance imaging (MRI) scan of their brain. This is when the person goes inside an MRI scanner to have a picture taken of the inside of the brain. These tests can help the doctor to find out which kind of epilepsy a person has, and which medicines will work best.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.