Types of Seizures

What is a seizure?

Seizure is an uncontrolled burst of electrical activity in brain cells (nerves/neurons) that causes temporary abnormalities in movements, muscle activity/tone, behaviours, sensations, or states of awareness. Seizures are not alike as symptoms can vary between people depending on the causes and simply on the person experiencing it. A seizure can be a single, acute event or it can recur. When a person has recurring seizures, this is known as epilepsy.

What are the main types of seizure?

This graphic gives a brief overview of current classification of seizures. Overall, we can group seizures into 3 categories: focal onset, generalized onset and unknown onset.

What are focal onset seizures?

Focal onset seizures start in one area and can spread across the brain and cause mild or severe symptoms, depending on how the electrical discharges spread. Person affected by a focal onset seizure can be fully aware or have impaired awareness during the episode.

During a focal aware seizure, a person could be fully aware of what’s happening around them but might not be able to respond. They are usually last a short amount of time and can be mistaken for daydreaming.

During a focal impaired awareness seizure, the person might appear confused and disoriented.

What are generalized onset seizures?

Generalised onset seizures affect both sides of the brain. A person affected by generalised seizures is not aware during the episode. Generalised seizures can be further divided in generalised motor or non-motor seizures.

Motor symptoms include:

• jerking of the limbs (clonic focal onset) or sustained rhythmical jerking movements (clonic generalised onset)
• muscles becoming limp or weak (atonic),
• tense or rigid muscles (tonic), brief muscle twitching (myoclonus),
• epileptic spasms – body flexes and extends repeatedly (focal and generalized onset)
• automatisms or repeated automatic movements, like clapping or rubbing of hands, lip-smacking or chewing, or running (focal onset)

Non-motor symptoms include:

• changes in sensation or emotions,
• changes in thinking or cognition,
• changes in autonomic functions (such as gastrointestinal sensations, waves of heat or cold, goosebumps, heart racing, etc.),
• lack of movement (called behaviour arrest)

What are other types of generalized onset seizures?

There are many types of seizures in this classification. They include:

• Absence – a sudden lapse in awareness and responsiveness that look like brief staring spells or daydreaming. This usually occurs in children.
• Tonic-Clonic – the body stiffens (the tonic phase) and then the limbs begin to jerk
• rhythmically (the clonic phase)
• Myoclonic – sudden single jerks of a muscle or a group of muscles that may last no more than a second or two
• Tonic – Can occur when a person is asleep or awake and involves a brief stiffening of the body, arms or legs. The person will suddenly fall if standing or sitting.
• Atonic – brief seizures that cause a sudden loss muscle tone and the person often falls to the ground or will have a sudden head nod if sitting.
• Clonic – although uncommon they cause jerking in various parts of the body

What are unknown onset seizures?

These seizures can’t be diagnosed as focal or generalised onset seizures at the time of presentation. When more information is obtained, they are further classified.

Summary

Epilepsy is a neurological disease of recurring seizures, which are caused by uncontrolled electrical activity within the brain.

These can cause multiple symptoms, such as a lack of consciousness, jerking of the limbs, a lack of control of the bladder, drowsiness and abnormal sensations and smells.

Epilepsy is divided into two main categories: generalised, where the whole brain is involved, and focal, where only a part of the brain is involved.

Epilepsy can then be subdivided depending on whether the person is aware of their surroundings during the episode, the muscles and movements involved, and other symptoms.

In cases where the type of seizure isn’t clear, the seizures are classified as ‘unknown onset’, until further testing can determine the diagnosis.