How Is Epilepsy Diagnosed?

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Epilepsy is a chronic neurological condition characterized by recurrent seizures. A seizure is a sudden flare of activity between your neurons—cells that transmit information in your brain. This can affect your nervous system and lead to common involuntary symptoms like sudden muscle contractions (called convulsions) and loss of consciousness.

Not everyone who has seizures has epilepsy, as a diagnosis for epilepsy usually requires having two or more unprovoked seizures greater than 24 hours apart.

Neurologists—doctors who treat the brain and nervous system—as well as other healthcare providers can diagnose epilepsy. Typically, the diagnostic process begins with discussing your medical history, followed by an electroencephalograph (EEG)—an imaging test that measures brain activity. Some diagnoses may require blood tests, additional imaging scans, and other tests to help determine the type of epilepsy you have and your health status.

A proper diagnosis can help your healthcare provider understand the best course of treatment for your condition. They can help you manage your symptoms and prevent complications.

Medical History

Your healthcare provider will ask about your medical history with seizures, including your symptoms, the frequency in which they occur, how long they last, and what warning signs appear before your seizures start. This information can help them pinpoint a diagnosis. Your medical history also includes past illnesses, other health conditions, medication, or a family history that could increase your risk of epilepsy. 

Often, people who experience the seizure can’t remember exactly what happened. Caregivers or other people who witnessed the seizure can help you gather this information to share with your provider.

Diagnostic Criteria for Type of Epilepsy

A neurologist can use your medical history and several tests to determine the type of seizures and form of epilepsy you have. They might use the following standard diagnostic criteria, which was developed by the International League Against Epilepsy—a global organization of health experts and researchers of epilepsy.

Seizure Type

The first level of diagnosis identifies where seizures start, which determines the seizure type:

  • Generalized onset seizure: This affects both sides of the brain. 
  • Focal onset seizure: This starts in one part of the brain, typically only affecting one side.
  • Unknown onset seizure: When the type of seizure isn’t clear, your healthcare provider may classify the onset as unknown.

Epilepsy Type

To determine the epilepsy type, a neurologist will use an electroencephalograph (EEG). To do this, they will attach an array of small discs (electrodes) to your scalp, which are connected to a machine that measures electrical activity across different regions of the brain.

Even if you do not have a seizure during an EEG, the test can show signs of unusual electrical activity. The brain signals look like waves with rising peaks and troughs. If there are spikes or sharp waves in the EEG recording, it shows that a region of the brain tends to develop seizures.

The major types of epilepsy and their symptoms include:

Generalized epilepsy: The EEG shows abnormal activity across the entire brain. This type of epilepsy can be further divided into one of the following subtypes, based on your symptoms:

  • Absence seizures (non-motor seizures): Staring absently into space, sometimes with muscle twitching (muscle spasms)
  • Myoclonic seizures: Muscle jerking (sudden uncontrolled movements) or twitching in the upper body, arms, or legs
  • Atonic seizures: Loss of muscle tension (muscle tone) that can result in falling down or head drooping
  • Tonic seizures: Muscle stiffening, usually in the back, arms, and legs
  • Tonic-clonic seizures (grand mal seizures): Muscle stiffening, loss of consciousness, and repeated muscle jerking in the arms and legs

Focal epilepsy: The EEG shows abnormal activity that starts on only one side of the brain. Subtypes of focal epilepsy can vary by awareness, motor symptoms, and brain activity. These include:

  • Aware seizures: Occurs while you are awake, conscious, and aware (formally called simple partial seizure)
  • Impaired awareness seizures: Occurs with confusion and lack of awareness (formally called complex partial seizure)
  • Motor seizures: Show symptoms that affect movement, such as muscle jerking (clonic), loss of muscle tension (atonic), tense or rigid muscles (tonic), muscle twitching (myoclonic), or epileptic spasms (brief stiffening of arms, legs, and head)
  • Non-motor seizures (absence seizures): Presence of absent staring, at times with brief twitching in the eyelids or in one part of the body
  • Focal to bilateral tonic-clonic seizures (secondarily generalized seizures): Starts on one side of the brain and spreads to both sides

Combined generalized and focal epilepsy: Some people will have both types of seizures described above. This occurs with some genetic conditions.

Unknown: This diagnosis is provided when a neurologist isn’t able to narrow down whether the epilepsy type is generalized or focal. Still, they may be to determine the symptom subtype:

  • Motor seizures: Tonic-clonic symptoms (muscle stiffening or jerking) or epileptic spasms 
  • Non-motor seizures: Movement stops (behavior arrest), including staring

Epilepsy Syndrome

Some forms of epilepsy can be further classified as a syndrome. An epilepsy syndrome is a group of seizures with similar features such as age of onset (when seizures began), symptoms, triggers, brain imaging results, genetic factors, occurrence by time of day, and other features.

Blood Tests

Your healthcare provider can take a blood sample and send it to a lab for testing. Blood tests can check for certain factors, such as hormone, protein, or cholesterol levels. These can help detect other health conditions such as anemia and diabetes, which may be an underlying cause or trigger for seizures.

Blood tests are also routinely used to assess these factors:

  • Infections
  • Complete blood count (a test that measured all the components of your blood)
  • Overall blood chemistry (a test that measures certain chemicals in your blood)

Genetic Testing

A genetic test for epilepsy is a type of blood test that can check whether you have certain genes commonly associated with different types of epilepsy. Some genes can be inherited in families and result in genetic conditions (such as SCN1A, CHRNA4, and LGI1), while others are gene variants that may not be inherited. 

There are multiple genes and genetic variants (formerly known as gene mutations) that scientists have identified to be associated with an increased risk of seizures. Generally, these genes affect the flow of electrical activity in the brain and can predispose someone to having seizures.

Other Imaging and Brain Function Tests

Aside from an EEG, there are other types of brain imaging tests and scans that can help diagnose epilepsy and monitor your brain function. 

Neurological Exam

A neurologist can conduct a manual neurological exam to assess your movement, behavior, memory, language ability, and other mental functions. This assessment may help when determining the type of epilepsy you have.

Magnetoencephalography (MEG)

A MEG is a non-invasive technique that maps brain activity by detecting magnetic signals from brain cells. They are especially useful for figuring out which parts of the brain produce a focal seizure. It helps identify the border between healthy and seizure-producing areas of the brain.

Computed Tomography (CT)

CT scans combine many X-ray images to get a detailed picture of the brain. It identifies structural abnormalities, including tumors or cysts, that can cause seizure symptoms.

Magnetic Resonance Imaging (MRI)

MRIs are non-invasive machines that use a magnetic field and radio waves to develop detailed images of the brain. These images can also show the brain’s internal structures. It can detect lesions (areas of damage) in the brain that contribute to focal epilepsy. However, if the epilepsy is not caused by a lesion, the MRI will not show any brain abnormalities.

Single-Photon Emission Computed Tomography (SPECT)

SPECT is an imaging technique that detects changes in blood flow during a seizure. Usually a spike of energy occurs during a seizure, leading to increased blood flow. 

During a hospital stay, a healthcare provider will inject a small amount of radioactive tracer within 30 seconds of a seizure. This tracer allows a SPECT scanner to spot the regions of the brain where the seizures started. This can be used to check if cognitive functions, like memory, are impaired in the epileptic region.

Wada Test

The Wada test may also help identify whether someone is a good candidate for surgery—a common treatment for some cases of epilepsy.

The Wada test can be used to assess your memory and language ability. The procedure involves injecting a sedative drug—either Amytal Sodium (sodium amobarbital) or Brevital (methohexital)—into one of your carotid arteries—which deliver blood from your heart to your head and neck. When the drug reaches the brain, it causes a one to five-minute paralysis of one side of the brain. 

In these five minutes, memory and language ability is tested in the non-paralyzed side of the brain. After, the neurologist will inject the medication into the other side of the brain and repeat the test. This is used in conjunction with other forms of imaging to verify the source of a seizure. 

Positron Emission Tomography (PET)

A PET scan is a form of imaging that measures the brain’s metabolism—how your brain uses energy. This scan is rarely used to diagnose epilepsy, but may be used if your neurologist suspects that you have a comorbid neurodegenerative disease to be diagnosed.

Before the scan, a neurologist will inject a small amount of radioactive sugar into your vein. The PET scanner can then take images of your brain regions.

Someone with epilepsy who is not experiencing a seizure has decreased metabolic function in the region of the brain that starts the seizures. If an MRI scan doesn’t show any lesions, a PET scan can detect other abnormalities in brain function.

Screening for Related Conditions

Not all seizures are caused by epilepsy. Figuring out what caused the seizure can help inform proper treatment. 

First Seizures

A first-time seizure, or first seizure, can be provoked by a variety of  factors. However, having a first seizure does not necessarily lead to the development of epilepsy. Some causes and conditions that may trigger a first seizure include:

  • Traumatic brain injury (TBI), which can be caused by a blow or jolt to the head resulting in immediate altered consciousness or neurological functioning
  • Stroke, such as a brain hemorrhage—when an artery in the brain ruptures and bleeds
  • Meningitis, or inflammation of the the brain and spinal cord membranes, often caused by a bacterial or viral infection
  • Encephalitis, or brain inflammation, often caused by a bacterial or viral infection
  • High blood pressure during pregnancy
  • Brain abscesses, which are swollen areas of pus, often due to a bacterial or fungal infection
  • Very high (hyperglycemia) or very low blood sugar (hypoglycemia)
  • Low sodium, calcium, or magnesium levels
  • Withdrawal from addictive substances and drugs

Febrile Seizures

Febrile seizures are very common in children under the age of 5. They are caused by fever that raises the body temperature above 100.4 degrees Fahrenheit. Often, the fever can occur following a viral or bacterial infection. These seizures likely will not cause long-term harm or ongoing neurological issues.

Non-Epileptic Events

A non-epileptic event resembles the symptoms of a seizure but, unlike an epileptic seizure, there is no underlying abnormal brain electrical activity during a non-epileptic seizure. Researchers aren’t sure what causes non-epileptic events. However, they hypothesize it involves stress and other psychological factors. 

Status Epilepticus

Status epilepticus is a potentially life-threatening condition associated with epilepsy. It is a medical emergency that requires urgent treatment and care. 

Status epilepticus can occur when a person has a prolonged seizure and does not fully regain consciousness. It can also occur if someone has repeated seizures in a row and does not regain consciousness in between. In general, if a seizure lasts for five minutes or more, it is considered status epilepticus. 

Depending on the symptoms, there are subtypes of this condition. Convulsive status epilepticus involves outward signs like jerking movements and other motor symptoms. A non-convulsive status epilepticus involves confusion, agitation, loss of consciousness, or coma. 

In the event of status epilepticus, a healthcare provider can provide an antiepileptic drug to slow or stop the seizure.

H3: Sudden Unexpected Death in Epilepsy (SUDEP)

Epilepsy is associated with a rare condition called sudden unexpected death in epilepsy (SUDEP). It can occur in people with epilepsy—with or without seizure activity. Researchers aren’t sure what causes SUDEP but suggest it involves complications in the heart and lungs. 

Responding to a Seizure

If you see someone who is having a seizure or is suddenly unconscious, check for a medical alert bracelet or ID and follow the directions indicated. If you cannot find one, call 9-1-1. Immediately seek out medical personnel, such as an emergency medical technician (EMT), a paramedic, or another healthcare provider.


A Quick Review

Epilepsy is a seizure disorder that is typically diagnosed by a neurologist. The diagnosis involves taking a medical history, measuring brain activity, and conducting various tests. A healthcare provider will determine the type of epilepsy and seizures, as well as use imaging scans, like an MRI, to assess your condition. 

It is important to differentiate epilepsy with provoked seizures, which could be caused by other life-threatening conditions. An accurate diagnosis informs treatment while making patients and their caregivers aware of associated conditions like status epilepticus and SUDEP.

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