Menu
Seizure Categories
Courtesy of the CEA, 2019
A special thank you to the Canadian Epilepsy Alliance for sharing their up to date and correct epilepsy information
Seizures are divided into three main categories: Focal Onset, Generalized Onset, or Unknown onset. The category is determined by the location of the seizure activity within the brain at the beginning of the seizure.
Seizures may also be described as either motor or nonmotor, depending on whether or not muscle movement is involved.
The description of what happens during the seizure, along with any changes that happen before or after the seizure, are important features used by a healthcare provider to determine the seizure category and the seizure type. The duration of the seizure is another important feature.
FOCAL SEZURES
Focal seizures start in a particular site, or ‘focus’, within one brain hemisphere. The location of the seizure activity in the brain will determine what the seizure will look or feel like.
A focal seizure in the part of the brain responsible for hearing could cause a sudden but temporary distortion in sound or the person could hear a sound that isn’t there (i.e. an auditory hallucination). A focal seizure in the part of the brain responsible for controlling finger movements could cause a sudden twitching of one or more fingers on the opposite side of the body.
Focal seizures can vary a lot from one person to another because of the wide range of functions that our brains control. However, an individual with a single seizure focus usually has the same experience each time their seizure starts.
FOCAL AWARE SEIZURES
During this type of seizure, a person will be alert, aware of everything that is happening, and able to have a conversation with others. People often refer to this seizure as an aura if they experience things that are not visible to others such as an unusual feeling.
Focal aware seizures could also result in visible changes, for example twitching of certain muscles on one side of the body or an uncontrollable movement.
FOCAL IMPAIRED AWARENESS SEIZURES
This type of focal seizure causes a change in awareness or in thinking abilities. During a focal impaired awareness seizure, a person may have trouble communicating or understanding language. They might have a blank stare and could be unresponsive. Some people exhibit repetitive movements or automatic behaviours, such as chewing movements, rearranging objects or fiddling with clothing. Healthcare providers call these behaviours “automatisms”. Some people wander during a focal impaired awareness seizure.
Some individuals who exhibit unusual behaviours during a focal impaired awareness seizure could be mistaken for being under the influence of alcohol or drugs. People could also be mistakenly viewed as uncooperative if they do not respond to someone’s questions or instructions during the seizure.
The seizure activity may remain in the part of the brain where it began, or it may spread to other areas in the brain. Some focal seizures evolve to a bilateral (both the left and right hemispheres) tonic-clonic seizure.
When a focal impaired awareness seizure ends, the person may initially be confused and disoriented. This can make it difficult to tell exactly when the seizure (or ictal period) has ended and the post-ictal phase that follows the seizure has begun.
FOCAL TO BILATERAL TONIC-CLONIC SEIZURE
Focal to bilateral tonic-clonic seizures start in a limited area on one side of the brain and spread to involve both sides. This differs from a generalized onset tonic-clonic seizure, which starts on both sides of the brain.
Another difference is that Focal onset seizures have an abnormal region of the brain leading to the electrical storm of a seizure. Testing may not detect the place or cause of focus, while Generalized onset seizures are believed to result from neurochemical and/or genetic abnormalities widespread throughout brain, and no focal injured brain region is involved.
Bilateral tonic-clonic seizures:
• happen in more than 3 out of 10 people with focal epilepsy.
• Sometimes the person will not recall the beginning of the seizure
• the seizure may spread quickly so the first part is hard to see. This part usually lasts seconds to less than a minute.
• The bilateral tonic-clonic part of these seizures usually lasts less than 2 or 3 minutes.
• After the seizure, consciousness returns slowly, and the person may be drowsy, confused, agitated, or depressed.
• Some people may need to rest for a few hours after a seizure, while others return to their pre- seizure state within minutes.
• If the person does not return to their pre-seizure state, or if another seizure occurs before they return to their pre seizure state, this may be a sign of a seizure emergency called status epilepticus.
• A person who has repeated or long tonic-clonic seizures (longer than 3 minutes) needs immediate medical help. Call 911.
• People who have had tonic-clonic seizures should talk to their health care team about first aid, when to go to the hospital, creating a seizure response plan, and whether rescue therapies are required.
GENERALIZED SEIZURES
Generalized seizures quickly spread across the left and right hemispheres of the brain. Many, but not all, generalized seizures are associated with a loss of awareness. Most generalized seizures cause changes in the body’s muscles, such as a stiffening of the muscles (tonic), a decrease in muscle tone (atonic), rhythmic jerking movements (clonic), or a sudden twitch or jolt-like movement (myoclonic). These various types of muscular changes are associated with different types of generalized seizures, as listed below, but could occur during focal seizures too.
There are six main types of generalized seizures: Tonic-Clonic, Absence, Clonic, Tonic, Atonic, and Myoclonic.
GENERALIZED OR UNKNOWN ONSET TONIC-CLONIC
For most people, this is the type of seizure they think of when they think of epilepsy. During the seizure there are two phases, tonic (a stiffening of the muscles) and clonic (rhythmic jerking of the muscles). These phases can happen in any order, but most often the tonic phase is first, followed by the clonic phase.
Generalized or Unknown Onset Tonic-Clonic seizures can occur if someone has generalized onset epilepsy and the seizure is a generalized seizure from the very start. A tonic-clonic seizure can also occur if someone has focal epilepsy if their focal seizure evolves to become a bilateral convulsive seizure. Generalized or Unknown Onset Tonic-Clonic seizures can also occur when people do not have epilepsy and can be brought on (or provoked) by various things such as fever, infection, low blood sugar, or alcohol withdrawal.
The typical length of a Generalized or Unknown Onset Tonic-Clonic seizure is from under a minute to a few minutes. Like other seizures, these seizures generally run their course and end naturally on their own. When the person regains consciousness, they will usually be confused and will gradually re-orient themselves to where they are and what has happened. People are often tired and sore after a Generalized or Unknown Onset Tonic-Clonic seizure and may want to rest.
GENERALIZED ABSENCE SEIZURES
These seizures are very brief, about 9 seconds on average. The most striking feature is a blank or vacant look that could be misinterpreted as a brief episode of daydreaming. The blank look may be the only outward sign, although some people have other features that could include eye movements, blinking or automatic behaviours.
A generalized absence seizure would typically start abruptly and end abruptly. After the brief seizure, the person will generally carry on with whatever they had been doing before. These seizures can go unnoticed, or, if noticed, they may not be recognized as being a seizure.
CLONIC SEIZURES
These seizures cause rhythmic jerking movements. When the rhythmic jerking movements are the only feature, it is a clonic seizure. These types of movements occur more frequently in association with a phase of muscle stiffening (see generalized or unknown onset tonic-clonic seizures above). These seizures may also have a focal onset.
TONIC SEIZURES
These seizures cause the muscles to stiffen. If a person is standing, a sudden increase in muscle tone could cause them to fall. Some people call this a “drop attack”. Generalized tonic seizures could also cause a sudden stiffening (or contraction) of the muscles in both arms. These seizures usually last less than 20 seconds, but sometimes they could be up to about 60 seconds.
These seizures may also have a focal onset.
FOCAL OR GENERALIZED ATONIC
These seizures cause a loss of muscle tone, which means the individual suddenly becomes limp. If a person is standing, the sudden loss of muscle tone will cause them to fall. Therefore, both generalized or unknown onset tonic seizures and focal or generalized atonic seizures can be associated with episodes that people may refer to as drop attacks.
These seizures may also have a focal onset.
FOCAL OR GENERALIZED MYOCLONIC
These seizures are extremely brief, jolt-like movements that resemble a startle response. For example, an individual could have a sudden jerk of their upper arms or shoulders. Sometimes the muscle contractions are subtle and may not be visible to an observer.
These seizures are usually less than a second in length. They may also have a focal onset.
WHAT ARE EPILEPSY SYNDROMES?
When a person’s seizure disorder has a characteristic group of features, it is called a syndrome. Syndromes have a cluster of symptoms or signs that define them. Some of the most common or well-defined epileptic syndromes are febrile seizures, infantile spasms, Lennox-Gastaut syndrome, Benign Rolandic epilepsy, juvenile myoclonic epilepsy, progressive myoclonic epilepsy, reflex epilepsies, temporal lobe epilepsy, and frontal lobe epilepsy.
WHAT IS STATUS EPILEPTICUS?
Seizures usually end naturally after a few seconds or minutes, but on rare occasions a seizure doesn’t stop. When a seizure goes on longer than 30 minutes, or repeats in a series, the person is in status epilepticus. This state of continuous seizure activity can happen with any type of seizure. Status epilepticus is considered a medical emergency. When a seizure is continuous for a period longer than 30 minutes, or repeats in a series without the individual regaining their normal level of consciousness during the 30-minute period, this is traditionally defined as a person in status epilepticus.
WHAT IS PHOTOSENSITIVE EPILEPSY?
Photosensitivity describes a sensitivity to flashing or flickering lights, usually of high intensity, which are pulsating in a regular pattern. Many people are uncomfortable when exposed to such lights, but people with photosensitive epilepsy can be triggered into seizures by them. When given an electroencephalogram (EEG test), the majority of such patients will show epileptiform brain discharges when exposed to flashing lights.
