Partial onset seizures, now officially called focal onset seizures, are the most common type of seizure in people with epilepsy. They account for roughly 55% of all epilepsy cases in both adults and children. The defining feature is that they start in one specific area on one side of the brain, rather than affecting the whole brain at once. The term “partial seizure” was replaced in 2017 by the International League Against Epilepsy because it was confusing to patients, but you’ll still see the older name used frequently by doctors and in older medical literature.
Why the Name Changed
For decades, these seizures were split into “simple partial” and “complex partial” categories. The problem was that those labels didn’t mean much to the people actually experiencing them. In 2017, the international body that classifies epilepsy updated the terminology. “Simple partial seizures” became “focal aware seizures,” meaning you stay conscious and alert during the episode. “Complex partial seizures” became “focal impaired awareness seizures,” meaning your consciousness is affected in some way. The new names describe what’s actually happening, which makes them easier to understand and communicate.
What Happens in the Brain
During a focal seizure, a burst of abnormal electrical activity fires in a localized cluster of neurons on one side of the brain. The symptoms you experience depend entirely on where that cluster is located. If it’s in the area that controls movement, you might have involuntary jerking in one hand or one side of your face. If it’s in a region tied to emotion or memory, you might feel sudden fear or an intense wave of déjà vu.
The temporal lobe is the most common origin point, especially for seizures that affect awareness. At least 10% to 30% of focal seizures with impaired awareness start outside the temporal lobe, with the frontal lobe being the next most common source (accounting for up to 30% of focal epilepsy cases). In adults over 24, focal seizures are at least twice as common as seizures that affect the whole brain from the start.
Focal Aware Seizures
These are the episodes where you remain fully conscious throughout. You know what’s happening, you can hear people talking to you, and you remember the event afterward. Despite that, the experience can be strange and unsettling. Common symptoms include a sudden rising sensation in the stomach, a powerful feeling of déjà vu, a wave of unexplained fear or joy, unusual tastes or smells, or tingling and twitching on one side of the body.
These episodes are sometimes called “auras,” particularly when they serve as a warning sign that a larger seizure is about to follow. They typically last seconds to a couple of minutes. Because the person looks relatively normal from the outside, focal aware seizures often go unrecognized or get dismissed as anxiety or daydreaming.
Focal Impaired Awareness Seizures
These seizures affect your level of consciousness. You may appear awake but look confused or dazed, and you won’t be able to respond normally to questions or directions. People in the middle of one of these episodes often perform repetitive, automatic movements: picking at their clothes, smacking their lips, fumbling with objects, or wandering aimlessly. These involuntary behaviors are called automatisms.
An episode typically lasts one to three minutes, followed by a period of confusion that can stretch from minutes to an hour. Most people have little or no memory of what happened during the seizure itself. Because the person is not fully aware and may be moving around, these seizures carry a higher safety risk than focal aware seizures. Someone having one near a stove, a road, or a body of water is in real danger.
Focal to Bilateral Tonic-Clonic Seizures
Sometimes a focal seizure spreads from its starting point to both sides of the brain. When this happens, it triggers what most people picture when they think of a seizure: the body stiffens, then jerks rhythmically, and the person loses consciousness completely. This progression used to be called “secondary generalization.” Recognizing that a convulsive seizure actually started as a focal one matters for treatment, because the medications and surgical options differ from those used for seizures that are generalized from the start.
Common Causes
In many cases, no clear structural cause is found on brain imaging. When a cause is identified, it varies by age. In children, abnormal brain development (particularly malformations in the outer layer of the brain) and low-grade brain tumors are the most common culprits. In older adults, cerebrovascular disease, including stroke, is the leading cause.
Other identified causes include prior head trauma, brain infections, hippocampal sclerosis (scarring in the memory-related part of the temporal lobe), abnormal blood vessel formations, and certain genetic conditions like tuberous sclerosis complex. A history of oxygen deprivation at birth can also set the stage for focal epilepsy later in life.
How Focal Seizures Are Diagnosed
An electroencephalogram (EEG) is the primary tool. It records electrical activity across the brain and can pick up abnormal spikes or waves concentrated in one region, pointing to a focal origin. A standard EEG might be normal between seizures, so doctors sometimes use prolonged monitoring over 24 to 72 hours to catch an actual episode.
Brain imaging with MRI helps identify structural causes like scarring, tumors, or malformations. In cases where seizures don’t respond to medication and surgery is being considered, more advanced techniques can combine EEG data with functional brain imaging to pinpoint the exact source of seizure activity with greater precision.
Treatment Options
Anti-seizure medications are the first line of treatment. Several medications have proven effective specifically for focal onset seizures, and the field has expanded considerably beyond older options. Historically, carbamazepine was the standard based on its strong balance of effectiveness and tolerability. Newer options that perform equally well or better in terms of side effects include lamotrigine, oxcarbazepine, levetiracetam, lacosamide, topiramate, and zonisamide.
The choice among these depends on your other health conditions, other medications you take, and how you tolerate side effects. Most people start on a single medication at a low dose that gets gradually increased. About one-third of people with focal epilepsy continue to have seizures despite trying multiple medications. For those with drug-resistant focal epilepsy, surgery to remove or disconnect the area where seizures originate can be highly effective, particularly when the seizure focus is clearly identified on imaging.
What to Do if Someone Has a Seizure
If you’re with someone having a focal seizure with impaired awareness, the most important thing is to stay calm and stay with them. Guide them away from anything dangerous, like traffic, sharp objects, or hot surfaces. Don’t restrain them or try to hold them still. Don’t put anything in their mouth.
If they’re lying down, gently roll them onto their side with their mouth pointing toward the ground to keep the airway clear. Time the seizure. If it lasts longer than five minutes, call 911. Once the seizure ends, help them sit somewhere safe, let them recover, and calmly explain what happened. Don’t offer food or water until they’re fully alert.