Focal vs. Generalized Tonic-Clonic Seizures: Key Differences
Two people can both have seizures where they stiffen, fall and jerk. One has generalized epilepsy. The other has focal epilepsy that spreads. They may need different medicines, and they would be considered for different research studies. The difference comes down to where the seizure starts.
Key takeaways
Focal seizures begin in one area on one side of the brain. Generalized seizures begin on both sides at the same time.
A focal seizure can spread and become a “focal to bilateral tonic-clonic” seizure, which can look just like a generalized one.
EEG, video-EEG and MRI help confirm where seizures start.
Seizure type guides medicine choice, and research studies often enroll one type only.
Focal seizures: starting in one area
The CDC describes focal (or focal onset) seizures as seizures that begin on one side of the brain. What a person experiences depends on the area involved:
Focal aware seizures: the person stays aware. They may notice a rising feeling in the stomach, a sudden emotion, tingling, a strange taste or jerking in one arm.
Focal impaired awareness seizures: awareness is affected. The person may stare, fumble with clothing, smack their lips or not respond, and often does not remember it.
Focal to bilateral tonic-clonic seizures: the seizure starts in one area, then spreads to both sides and becomes a full convulsion.
Generalized tonic-clonic seizures: both sides from the start
Generalized seizures begin, or appear to begin, on both sides of the brain at once. In a tonic-clonic seizure, formerly called "grand mal," the person loses consciousness, the body stiffens (tonic phase) and then jerks rhythmically (clonic phase). It usually lasts a few minutes, followed by confusion and tiredness. When this happens in someone with generalized epilepsy, doctors call it a primary generalized tonic-clonic seizure.
The key differences at a glance
Where it starts: focal seizures begin in one area on one side of the brain. Primary generalized tonic-clonic seizures begin on both sides at the same time.
Awareness: during a focal seizure it may be kept or impaired. In a generalized tonic-clonic seizure it is lost from the start.
Warning (aura): common before focal seizures, since an aura is itself a focal aware seizure. Usually absent before generalized ones.
Convulsions: a focal seizure becomes one only if it spreads to both sides. A generalized tonic-clonic seizure is a convulsion from the start.
Typical age of onset: focal epilepsy can begin at any age. Generalized epilepsies often begin in childhood, adolescence or early adulthood.
Why an aura is a useful clue
If you notice a warning feeling before a convulsion, such as déjà vu, a smell or a rising sensation, tell your neurologist. It suggests the seizure may start focally, even if it ends as a full tonic-clonic seizure.
How doctors tell them apart
Descriptions from witnesses help, but they can mislead because the start of a seizure is often missed. Doctors rely on:
EEG: brain wave patterns between seizures often point toward focal or generalized epilepsy.
Video-EEG monitoring: a hospital stay that records seizures on video and EEG at the same time.
MRI: can show a scar, malformation or other structural cause behind focal seizures.
Phone videos: a short clip from a family member, taken safely, can be very helpful. Our seizure diary guide covers what else to note.
Why the type changes treatment
Some medicines work across many seizure types. Others are designed mainly for focal seizures, and a few of those can make certain generalized seizures, such as absence or myoclonic seizures, worse. Getting the type right can be the difference between ongoing seizures and better control. If you have tried several medicines without success, it may be worth asking whether your seizure type has been confirmed with video-EEG. Learn more in when seizures continue despite medication.
Know your seizure type, or not quite sure? Our questionnaire covers both.
Why research studies focus on one seizure type
Because focal and generalized epilepsies behave differently, trials usually study them separately. Two Phase 3 studies of the investigational medicine XEN1101 (azetukalner) are a good example:
Study snapshot: two Phase 3 epilepsy studies
What is being studied
XEN1101 (azetukalner), an investigational once-daily capsule taken with the evening meal. It is designed to act on Kv7 potassium channels, which help calm overactive electrical signals in brain cells.
How it is tested
Added to a person's current seizure medicines and compared with placebo in a randomized, double-blind design. A baseline period of up to about 9.5 weeks is followed by 12 weeks of blinded treatment.
X-ACKT (NCT05667142)
People aged 12 and older with generalized epilepsy who have primary generalized tonic-clonic seizures, have tried at least two seizure medicines, and currently take 1 to 3.
X-TOLE3 (NCT05716100)
Adults aged 18 and older with focal epilepsy diagnosed at least two years ago, who have tried at least two seizure medicines and currently take 1 to 3.
After the blinded period
People who complete the 12 weeks may be able to join a separate open-label extension study, where everyone receives XEN1101.
Where
X-ACKT has dozens of research sites across the U.S., including epilepsy centers in Boston, Philadelphia, Atlanta, Houston, Cleveland, Seattle and Los Angeles. The study team can tell you the nearest site for either study.
X-ACKT does not include people who also have a focal seizure diagnosis, which is why an accurate diagnosis matters. Parents of teens can read our guide for families of teenagers with seizures.
Frequently asked questions
What is the difference between focal and generalized seizures?
Focal seizures start in one area on one side of the brain. Generalized seizures start on both sides of the brain at the same time. A focal seizure can spread to both sides and become a tonic-clonic seizure.
Is a grand mal seizure the same as a tonic-clonic seizure?
Yes. Grand mal is the older name. Tonic-clonic seizures involve loss of consciousness, stiffening and rhythmic jerking.
What is a focal to bilateral tonic-clonic seizure?
It is a seizure that starts in one area of the brain and spreads to both sides, becoming a convulsion. It can look like a primary generalized tonic-clonic seizure, so tests such as EEG help tell them apart.
I do not know my seizure type. Can I still check study eligibility?
Yes. The questionnaire includes an option for people who are unsure, and the study team works with your medical records to confirm your diagnosis.