What are focal onset seizures?

Telling one seizure type from another can be confusing to say the least as there are many different types of seizures. All of them can be classified by their ‘onset’ which refers to where in the brain the seizure originates from. 

Understanding the difference between types of seizure onsets and being able to recognise them can go a long way in helping form a diagnosis. It can also mean being better prepared to keep someone safe while they have a seizure. The type of seizure onset influences the choice of seizure medication, possibilities of surgery, management outcomes, and possible causes.

What are focal onset seizures?

Seizures are placed in three main categories: 

  1. Focal, 
  2. generalised, and 
  3. unknown onsets.  

[Image description: An illustration of two brains. One brain demonstrates a focal seizure and shows a seizure happening in one part of the brain. The other brain demonstrates a generalised seizure where the seizure is occurring all over the brain.]

A focal onset seizure describes a seizure that comes from (‘onset’) one area or side (‘focal’) of the brain. 

Around 60% of people with epilepsy have focal onset seizures, previously called partial seizures. These result from an abnormal electrical discharge originating from one area or side of the brain. The discharge may only affect that region of the brain or it may spread and become a focal to bilateral seizure, affecting both sides of the brain and changing how the seizure appears. 

Focal seizures present different symptoms to generalised seizures because they don’t affect both sides of the brain at onset.

Having said that, sometimes focal seizures can spread to involve the whole brain and become generalised seizures. 

[Image description: An illustration showing how a focal seizure can become a generalised seizure. The brain on the left shows a seizure starting off in one section of the brain (focal). Next to the brain is an arrow pointing to the right with text below, “seizure activity spreads”. The brain on the right shows how the seizure activity is now all over the brain, demonstrating a generalised seizure.]

How to recognise a focal onset seizure?

The first challenge in recognising a focal onset seizure is recognising that what’s happening is in fact a seizure in the first place. For some pointers on recognising these seizures check out this article and feel more confident to know when it’s happening. Once you’re comfortable with that, let’s look more closely at how to tell the difference between a focal and generalised onset seizures.

By observing the ways in which a seizure presents clinically — that is, looking at what the person is doing during the seizure — we can figure out if a seizure is likely to be a focal onset seizure.

Focal Generalised Unknown
  • The person may notice a strange sensation, smell, sound, taste or feeling known as an aura.
  • Jerking, shaking or contracting movements on one side of the body
  • For some — awareness is maintained as the event occurs — the person knows what is happening, who they are and where they are and can respond.
  • For others — loss, either partially or completely, of awareness — the person may become confused and is not able to respond clearly.
  • Nonpurposeful, stereotypical repetitive behaviours. This can appear as fidgeting, fumbling or lip-smacking.
  • No warning that a seizure is about to happen.
  • Limbs on both sides jerking, shaking or contracting in time (synchronously) with each other. This is known as tonic-clonic.
  • Awareness and responsiveness are lost completely.
  • The entire body becomes stiff. This is known as tonic.
  • Entire body losses tone causing collapse. This known as atonic.
  • Incontinence may occur.
  • May bite tongue or inside of their cheek.
  • Breathing affected causing cyanosis (blue lips).
  • May cry out or scream.
  • No warning that a seizure is about to happen.
  • No obvious movements.
  • Awareness was not tested.

One reason focal seizures can be hard to recognise is the similarity they can have with other conditions. It’s important to be aware that focal seizures symptoms can often be mistaken for other illnesses, so don’t ignore or mistreat any symptoms.

Some seizure imitators are:

  • Syncope
  • Migraines
  • Vertigo
  • Movement disorders
  • Behavioural or psychiatric
  • Sleep disorders
  • Daydreaming
  • Stroke
  • Heart attack

What happens during a focal onset seizure?

As you’re reading this your brain is continuously firing away countless small electrical impulses. These are responsible for coordinating everything you do from moving, thinking, speaking, remembering and much more. Some are converting the light reaching your eyes into visual pictures, others are working to help you comprehend this information and commit the parts you find interesting to memory, while other electrical impulses will be controlling the regulation of your body temperature and maintaining your posture. All these impulses work independently, travelling along cells called neurons and passing along messages in the chemical form called neurotransmitters. 

Damage to these neurons in one particular area, such as a traumatic brain injury, stroke or a tumour, can result in the electrical impulses becoming hyper synchronised i.e. all firing at the same time in a large uncontrolled burst. This disrupts all the normal impulses in that area causing a loss of normal function. The result is a focal onset seizure. 

What happens to the body when a focal seizure begins depends on where in the brain it is happening. Different areas of the brain control different functions. For example, one area of the brain just above your temple is responsible for producing speech and seizures originating here will therefore impair or block speech.

Whether they have been able to tell you they can feel a focal seizure coming on or you can read the signs yourself, here’s what to do when someone is having a seizure:

  • Make sure that person is safe where they are — Avoid moving them if possible. Move nearby objects if they are at risk of injuring themselves if they fall or lose control of their body movements. It’s important to act quickly to bring other people’s attention to the situation and help get them to a position of safety, especially if they are in a swimming pool, driving, or crossing the road. 
  • Time it — Once a seizure starts there is nothing you can do to stop it but it is important to monitor how long it lasts. If a seizure goes for longer than five (5) minutes then call ‘000’.
  • Roll into the recovery position — If the seizure results in a loss of consciousness, roll the person into the recovery position, clearing their airways to prevent them from choking. 
  • Stay with them — The person may become confused and distressed after a seizure. Help by reassuring them and keeping them calm.

Take a look at this article for more information on what to do when someone is having a seizure.

Woman Placing Man In Recovery Position After Accident

[Image description: A person is lying on the floor during a seizure. Another person is holding the head of the other individual to protect it from injury.]

Types of focal onset seizures

Focal seizures are categorised based on the person’s level of awareness and whether or not they have a loss in motor control during their event. 

Focal onset aware seizures

Previously referred to as focal simple onset, during these events the person remains aware of the surroundings and what is happening, even if they cannot move or respond.

Focal onset impaired awareness seizures

Previously referred to as focal complex seizures, the person loses a level of awareness during the event.

Focal motor or non-motor

The motor cortex is the area of the brain responsible for planning, coordinating and signalling movement in the body. Focal aware or impaired awareness seizures may cause uncontrolled movements such as jerking, twitching or repetitive movements if the seizure is occurring in the region of the motor cortex. These are described as focal motor seizures. What type of movements they are, and on what side of the body they occur can tell us a lot about the area of the brain the seizure is coming from.

Focal non-motor seizures occur where the person is having emotional, sensory or behavioural symptoms but no involuntary movements are seen.

What causes focal onset seizures? 

It can be very challenging to trace back the exact cause of an individual’s epilepsy and for many people it remains up to speculation. Focal epilepsies are most commonly caused by damage to or distorted neural tissue, such as:

  • Traumatic brain injury
  • Stroke
  • Tumours or lesions 
  • Developmental disorders
  • Infection

These causes lower the brain’s threshold for firing neurons which leads to having a seizure.

Triggers, different from causes, are external factors that provoke seizures in people with pre-existing epilepsy conditions. Triggers are factors that bring a person past that seizure threshold. 

Here are some examples of seizure triggers:

  • Sleep deprivation
  • Stress
  • Alcohol or drug use
  • Flashing lights
  • Certain foods
  • Time of day

When to speak to a doctor

Focal seizures can be hard to spot or realise they are happening. If you or your family members are concerned about unusual symptoms that come in episodes it might be time to speak to your doctor.

Try to provide as detailed a description of the events as you can. Filming videos on your mobile phone is very helpful.Think about if there are any patterns or triggers related to the event. When did they start? How frequent are they? The key to uncovering what’s going on is gathering as much information as possible about the events.

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