May 21, 2021

What is the difference between generalized and focal seizures?

About Epilepsy

Do you know the difference between focal and generalized onset seizures? Read our overview and understand how they affect the brain.

Has your doctor spoken to you about ‘focal onset’ or ‘generalized onset’ seizures? Physicians use these words to describe where in the brain a seizure started – but medical terms are often confusing!

So, here’s everything you need to know about the difference between generalized and focal seizures. 

Focal vs generalized seizures

Seizures happen because of electrical discharges in the brain. When treating your seizures, doctors try to find out where in your brain abnormal electrical patterns start happening (this is known as ‘onset’). If they can find out, it might affect the kind of treatment they offer. The electrical patterns are also called discharges and can happen in two ways: generalized and focal. 

What is a generalized seizure?

This is when the electrical discharge happens in many different parts (both sides) of the brain and starts at the same time. About 40% of people with epilepsy have generalized onset seizures. 

Types of generalized seizure include:

  • Absence seizures (staring spells)
  • Atonic seizures (when your muscles go limp suddenly and you may fall over)
  • Myoclonic seizures (these are sudden jerks in your muscles)
  • Tonic clonic seizures (where you fall to the ground then shake)

What causes a focal seizure?

With a focal seizure, the electrical discharge starts in only one side of the brain and may stay there. But focal seizures sometimes spread to the whole brain and this is called a secondary generalized seizure. About 60% of people with epilepsy experience focal onset seizures. 

Types of focal seizure include:

  • Focal aware (when you understand what’s happening but cannot control it)
  • Focal impaired awareness (you are confused or not conscious of what’s happening)
  • Focal motor seizures (you will twitch and jerk a little, or walk around aimlessly)
  • Focal non-motor (you won’t move, but instead have intense feelings and emotions such as hot and cold, fear, or a rising stomach)

Depending on whether you have a generalized or focal onset seizure, what you experience before, during and after a seizure may be different.

Introduction to… Absence seizures

Similarities between focal and generalized onset seizures

While the symptoms are different, the phases of generalized seizures and focal seizures are the same:

  1. Beginning phase (prodrome)

You may notice mood changes or an ‘aura’ which tells you a seizure is coming soon

  1. Middle phase (ictal)

This is when intense electrical activity happens in the brain and symptoms of seizures occur

  1. Ending phase (postictal)

This is the recovery stage, where you experience the aftereffects of having a seizures, such as tiredness, frustration, sickness and confusion

Keep learning: What happens in your brain during a seizure?

Diagnosing focal vs generalized seizures

When you are first diagnosed with epilepsy, your treatment team will want to work out if you have focal or generalized seizures. This information will help them decide which treatment plan is best for you. 

For example, the drugs carbamazepine and lamotrigine are often used to treat focal seizures, while sodium valproate is often used for generalized tonic-clonic seizures. 

To work out if you have focal or generalized onset seizures, the treatment team may use an EEG, an MRI or visual observation. It can also be helpful to ask someone who’s seen your seizures to record a video or provide a detailed description. This might help identify the type of seizures you have. 

Learn more about seizures

Focal vs generalized seizures is the main division of seizures types. But within each of these two categories there are many other types of seizure and epilepsy syndrome. Learn more about specific types of seizures and syndrome in our blogs