Understanding epilepsy
Epilepsy is not one disease with one cause. Different biological processes can make a brain more likely to generate recurrent epileptic seizures, and sometimes more than one cause category applies to the same person.
Central point: Finding a cause can influence treatment, prognosis, genetic counselling, surgery assessment and the way epilepsy is explained — but not finding a cause does not make the epilepsy less real.
The six broad cause categories
The International League Against Epilepsy (ILAE) groups the causes, or aetiologies, of epilepsy into six broad categories: structural, genetic, infectious, metabolic, immune and unknown. These categories are not a hierarchy. A person may fit more than one at the same time.
Structural
A structural cause means there is an abnormality of brain structure that is judged, together with the clinical picture, to be likely to cause the seizures. Examples include stroke, traumatic brain injury, some brain tumours, hippocampal sclerosis and malformations of cortical development such as focal cortical dysplasia.
Structural does not necessarily mean acquired. Some structural abnormalities have a genetic basis. This is one reason a person’s epilepsy can belong to more than one cause category.
Explore Structural & Acquired Epilepsies → for detailed pages on hippocampal sclerosis, focal cortical dysplasia, post-stroke epilepsy and other structural causes.
Genetic
A genetic cause means that epilepsy is understood to result directly from a known or presumed genetic variation. This does not automatically mean the epilepsy was inherited from a parent. A genetic change may be inherited, may arise for the first time in that person, or the exact genetic change may not yet be identified even when the overall syndrome strongly suggests a genetic basis.
Genetic testing is most useful in selected clinical situations. NICE recommends specialist discussion about whether testing is appropriate and highlights circumstances such as very early-onset epilepsy, a suspected genetic epilepsy syndrome, learning disability, autism, congenital abnormalities or unexplained cognitive decline.
Infectious
An infectious cause means epilepsy develops as a consequence of infection affecting the brain. Examples include encephalitis, meningitis and neurocysticercosis. The infections associated with epilepsy vary around the world, so infectious causes are particularly important when considering epilepsy globally.
Sometimes the active infection has resolved long before recurrent unprovoked seizures begin. In other situations a seizure occurs during an acute infection; that distinction matters because an acute symptomatic seizure is not automatically the same as epilepsy.
Metabolic
In metabolic epilepsies, an inherited or acquired metabolic disorder is the underlying reason the brain has a persistent tendency to generate seizures. This category refers to specific metabolic diseases that cause epilepsy, rather than every temporary disturbance of body chemistry that can provoke a seizure.
For example, severe hypoglycaemia can cause an acute seizure, but that does not by itself mean a person has a metabolic epilepsy. The clinical context determines whether the event is an acute symptomatic seizure or part of an enduring epilepsy disorder.
Explore Metabolic Epilepsies → for the difference between metabolic epilepsy and acute metabolic triggers, examples of treatable metabolic causes, diagnostic clues and worldwide access issues.
Immune
An immune cause is considered when an immune process is understood to be directly responsible for the epilepsy. Autoimmune encephalitis is an important example. These cases may present with new-onset seizures alongside changes in memory, behaviour, cognition, movement or level of consciousness.
NICE advises considering antibody testing, in discussion with a neurologist, when autoimmune encephalitis is suspected in someone with new-onset epilepsy. Antibody testing is not a routine test for every person with seizures.
Unknown
Unknown means the cause has not been identified with the evidence currently available. It does not mean there is no biological cause, and it does not mean the seizures are unexplained because they are psychological.
WHO notes that the underlying cause remains unknown in around half of epilepsy cases globally. Better imaging, genetics, immune testing and future research may allow some people currently placed in the unknown group to be reclassified later.
More than one category can apply
The ILAE framework deliberately allows more than one aetiology. For example, a genetic condition may produce a structural brain abnormality that is itself responsible for seizures. Both descriptions can be clinically useful: the structural finding may matter when considering epilepsy surgery, while the genetic diagnosis may matter for counselling, family testing or targeted treatment.
A cause is not the same as a trigger
This distinction is important. A cause explains why someone has an enduring predisposition to epileptic seizures. A trigger is something that can make a seizure more likely in a person who already has that predisposition — for example sleep deprivation or missed antiseizure medication in some people.
A trigger does not necessarily explain why the epilepsy developed in the first place.
A seizure caused by an acute problem is not automatically epilepsy
Seizures can occur during acute illnesses or disturbances such as severe hypoglycaemia, acute brain injury, intoxication or withdrawal. These events require medical assessment, but they are not automatically evidence of an enduring epileptic disorder. This distinction is explored in our page on acute symptomatic and provoked seizures.
How clinicians look for a cause
The investigation depends on the person’s history, examination, age, seizure pattern and other clinical features. It may involve MRI or other neuroimaging, EEG, genetic testing, blood or metabolic investigations, and selected immune or infectious testing. Not everyone needs every test.
NICE recommends neuroimaging when a structural cause is suspected, specialist consideration of genetic testing in selected cases, and antibody testing when autoimmune encephalitis is suspected.
Why finding the cause matters
An aetiological diagnosis can affect treatment choices, whether surgery or another specialist treatment is considered, genetic counselling, investigation of associated health problems and discussions about prognosis. In some cases it may identify a condition for which treatment is directed at the underlying disease as well as the seizures.
But a person’s epilepsy remains valid even when the cause is unknown. Diagnosis is based on the overall clinical evidence, not on finding a visible lesion or a positive genetic test.
Related pages
What Is Epilepsy? · Diagnosis and Tests · Genetics & Epilepsy · Treatment Options
Sources
International League Against Epilepsy — Classification of the Epilepsies
World Health Organization — Epilepsy fact sheet
NICE NG217 — Diagnosis and assessment of epilepsy
This page provides general educational information and is not individual medical advice. New or changing seizures, suspected first seizures, or concerns about an underlying cause should be assessed by an appropriate healthcare professional.