There are four recognized types of epilepsy: focal, generalized, combined focal and generalized, and unknown. But that number only tells part of the story. Epilepsy classification works on multiple levels, and doctors also categorize epilepsy by the specific syndrome a person has and by what’s causing it. Depending on how you count, there are dozens of distinct epilepsy syndromes, each with its own pattern of seizures, age of onset, and outlook.
The Four Epilepsy Types
The International League Against Epilepsy (ILAE), the organization that sets the global standard for epilepsy diagnosis, defines four broad epilepsy types based on where seizures originate in the brain and how they spread.
- Focal epilepsy involves seizures that start on one side of the brain. This is the most common type, accounting for roughly two to six times as many cases as generalized epilepsy. Seizures may cause changes in awareness, unusual movements on one side of the body, or odd sensations.
- Generalized epilepsy involves seizures that begin on both sides of the brain simultaneously. These seizures typically cause loss of consciousness and may produce abnormal movements affecting both sides of the body. Generalized epilepsy makes up about 23% to 35% of all epilepsy cases.
- Combined focal and generalized epilepsy means a person experiences both types of seizures. Dravet syndrome and Lennox-Gastaut syndrome are two well-known conditions that fall into this category, where EEG recordings show patterns associated with both focal and generalized activity.
- Unknown epilepsy is the classification used when there isn’t enough information to place someone in one of the other three categories. A person might have seizures that can’t be clearly characterized, along with normal EEG results, making it impossible to determine the seizure’s origin.
How the Classification System Works
Epilepsy diagnosis follows a three-level framework. The first level is identifying the seizure type: focal onset, generalized onset, or unknown onset. Focal seizures start in one area of the brain and may or may not affect consciousness. Generalized seizures appear to engage both hemispheres from the start.
The second level is determining the epilepsy type, which is where those four categories above come in. A person who only has focal seizures has focal epilepsy. Someone with both focal and generalized seizures has combined epilepsy. This level takes into account not just individual seizures but the overall pattern, including EEG findings and brain imaging.
The third level is identifying a specific epilepsy syndrome, if one fits. Syndromes are defined by a cluster of features: the types of seizures involved, the age they started, EEG patterns, and sometimes genetic findings. Not everyone with epilepsy fits neatly into a recognized syndrome, but when they do, it gives doctors a much clearer picture of what to expect and how to treat it.
Epilepsy Syndromes by Age of Onset
The ILAE defined a comprehensive list of epilepsy syndromes in 2022, organized into groups based on when seizures first appear. There are syndromes that begin in newborns and infants (up to age two), syndromes that begin in childhood, and syndromes that can start at various ages in both children and adults. A separate group covers the idiopathic generalized epilepsies, which include some of the most common forms of epilepsy worldwide.
Neonatal and Infant Syndromes
Some epilepsy syndromes appear in the first months or years of life. Several of these are self-limited, meaning seizures typically resolve on their own. Self-limited neonatal epilepsy and self-limited infantile epilepsy fall into this group, and many have a genetic basis that runs in families.
Other infant-onset syndromes are far more serious. Dravet syndrome usually begins in the first year of life and involves prolonged seizures often triggered by fever, with developmental delays that become apparent over time. Infantile epileptic spasms syndrome causes brief clusters of jerking movements and can significantly affect development. Early-infantile developmental and epileptic encephalopathy is another severe form where both the seizures themselves and the underlying brain condition impair development.
Childhood Syndromes
Several epilepsy syndromes emerge during childhood and have a generally favorable outlook. Self-limited epilepsy with centrotemporal spikes (sometimes still called benign rolandic epilepsy) is one of the most common childhood epilepsy syndromes. It causes focal seizures, often during sleep, and virtually all children outgrow it by adolescence. Self-limited epilepsy with autonomic seizures and childhood occipital visual epilepsy follow a similar pattern of remission.
Childhood absence epilepsy is another common syndrome, causing brief staring spells that can happen dozens of times a day. It’s classified as an idiopathic generalized epilepsy, meaning it has a presumed genetic basis without any structural brain abnormality. Most children respond well to treatment, though some go on to develop other seizure types in adolescence.
On the more severe end, Lennox-Gastaut syndrome typically starts between ages three and five and involves multiple seizure types that are often difficult to control. It’s associated with intellectual disability and tends to persist into adulthood.
Variable-Age Syndromes
Some epilepsy syndromes don’t have a fixed window of onset. Genetic epilepsy with febrile seizures plus (GEFS+) can appear in infancy or childhood and involves seizures triggered by fever that continue beyond the age when typical febrile seizures stop. Epilepsy with eyelid myoclonia causes brief jerks of the eyelids, often triggered by closing the eyes or by flashing lights, and can begin anywhere from childhood into early adulthood.
Six Causes of Epilepsy
Alongside seizure type and epilepsy type, doctors classify epilepsy by its underlying cause. The ILAE recognizes six etiological categories, and a single person’s epilepsy can fall into more than one.
- Genetic: A known or presumed genetic change is the direct cause of seizures. This doesn’t always mean inherited. Some genetic mutations occur spontaneously.
- Structural: A visible abnormality in the brain is responsible. This could be damage from a stroke, a brain tumor, a malformation that formed before birth, or scarring from a head injury.
- Metabolic: A metabolic disorder disrupts brain function and leads to seizures. These are often genetic in origin but are classified separately because the metabolic problem itself is what drives the seizures.
- Immune: The body’s immune system attacks the brain, causing inflammation that triggers seizures. Autoimmune encephalitis is one example.
- Infectious: An infection in the brain, such as meningitis, encephalitis, or certain parasitic infections, causes seizures. This is one of the most common causes of epilepsy worldwide.
- Unknown: No cause has been identified despite investigation.
Older terms like “idiopathic,” “cryptogenic,” and “symptomatic” are no longer used in formal classification. They’ve been replaced by these more precise categories as advances in brain imaging and genetic testing have made it possible to pinpoint causes that were previously undetectable.
How Epilepsy Type Is Determined
Two tools do most of the heavy lifting in epilepsy classification. An EEG records electrical activity in the brain through sensors placed on the scalp. Even between seizures, people with epilepsy often show characteristic patterns in their brain waves that help identify whether the epilepsy is focal or generalized. High-density EEG can pinpoint more precisely which brain regions are involved. If a seizure is captured during recording, it provides even more definitive information about where it starts and how it spreads.
An MRI creates detailed images of the brain’s structure and can reveal abnormalities like tumors, scarring, or developmental malformations that may be causing seizures. Together, EEG and MRI findings are combined with a person’s seizure history, age of onset, family history, and sometimes genetic testing to arrive at a complete classification: seizure type, epilepsy type, syndrome (if applicable), and cause.
For some people, all of this still doesn’t produce a clear answer. When EEG results are normal and seizures can’t be precisely characterized, the diagnosis stays at “unknown” for both seizure type and epilepsy type. This isn’t a failure of the process. It simply reflects the limits of available information at that point in time, and the classification can be updated as more data becomes available.