There are three classifications of seizure types. Generalised Onset is where the seizure starts and affects only one side of the brain. Focal Onset is where the seizure affects both sides of the brain. Unknown Onset seizure is where the area of the brain that is affected is not known. It is also possible for a focal seizure to spread to the whole brain and become a generalized seizure.
The following is a brief description of the more common seizures within these classifications:
An Absence seizure is a generalized seizure and they are brief. They may appear as a vacant stare some facial twitching and/or a rolling of the eyes. The person may show distinct behaviours prior to the seizure e.g. eye blinking, chewing movements, lip smacking, slight jerking movements of the lips or rubbing of the fingers/hands or other small hand movements..The seizures can be so brief that a person experiencing one is mistakenly thought to be ‘day-dreaming’.
A Tonic Clonic seizure involves a loss of consciousness, stiffening of muscle and muscle groups, followed by the shaking of the body .The stiffening of the muscles is the tonic phase and the clonic phase is the shaking movements.
A person experiencing this type of seizure may produce excess saliva, go blue in the face, lose control of their bladder and/or bowel, or bite their tongue and/or cheek. The person may also create vocal noises as the muscles in the chest contract and the air rushes through the vocal cords.
These seizures lasts for one to three minutes and the person often feels sleepy, confused or tired after the seizure. If a tonic-clonic seizure lasts for more than 5 minutes, it is considered a medical emergency and an ambulance should be called. If you witness a stranger experiencing a tonic-clonic seizure, an ambulance should be called irrespective of how long the seizure lasts.
A Myoclonic seizure is a brief shock like jerks of a muscle or groups of muscle, this only lasts for a couple of seconds and this may occur once or repetitive. When the seizure ends, the person is usually awake and alert, and can usually continue with what they were doing prior to the seizure.
A Tonic seizure causes the person’s body, arm and legs to become stiff and rigid (Tonic-stiffening of muscles) and may cause a person to fall and injure themselves. This type of seizure often occurs during sleep. Tonic seizures are usually brief, lasting around 20 seconds.
Atonic seizure causes a sudden loss or decrease of muscle tone, with the person to falling to the ground if standing prior to seizure. Atonic seizures usually involve both sides of the brain and typically last for less than 15 seconds. These seizures are often referred to as ‘drop attacks’ or ‘drop seizures’. Again, wearing a protective helmet is recommended.
During these seizures the person is aware and may experience feelings such as déjà vu, an unpleasant smell or taste, or sensations such as ‘butterflies’ or nausea. These seizures may also involve motor activity (such as involuntary and brief jerking of an arm or leg) or autonomic behaviours (such as fiddling with clothing or pointing).
In some cases, this type of seizure can come before another seizure type (e.g. tonic-clonic seizure). A feeling or movement that indicates a bigger seizure is going to happen is sometimes called an ‘aura’, although they are actually part of the seizure.
During these seizures the person may appear confused and dazed, and may do strange and repetitive actions (such as fiddling with their clothes, making chewing movements with their mouth or uttering unusual sounds). Following the seizure the person is likely to be confused, drowsy and may have a headache.
For some people, despite lots of tests and investigations, the type of seizure is unclear as to whether it is a focal or generalized onset, and is described as Unknown Onset. These seizures may be described as being Motor (symptoms include involvement of muscles) or Non-Motor (symptoms do not involve muscles). People may experience varied states of awareness.
Not all seizures have epilepsy as a cause. Some people experience symptoms which are similar to that of an epileptic seizure but without the unusual electrical brain activity. This is known as a psychogenic non-epileptic seizure (PNES). These seizures are very real to the person experiencing them, and they have no conscious or voluntary control over them. Outwardly, these seizures resemble epileptic seizure types and can occur at any age. PNES are believed to be complex physical reactions to significant psychological stresses.
Around 20% – 30% of patients referred to epilepsy centres for uncontrolled seizures are subsequently diagnosed with PNES. If a neurologist suspects that a person is experiencing PNES, they will conduct diagnostic tests to rule out epilepsy. Once it is determined that epilepsy is not the cause then other conditions which resemble seizures will also need to be discounted. This may include investigations to rule out heart disease, stroke, fainting and neuromuscular disorders. If these tests prove negative, then a psychological or psychiatric assessment is recommended in order to diagnose PNES.
Factors that may make a person vulnerable to developing PNES can include inherited factors, and difficult early experiences, including trauma. PNES may also start when people face difficulties or trauma in adulthood (e.g. unexpected life events, such as a death, accident, health problems or personal dilemmas).
For some people, a diagnosis of PNES may be a relief because there is no underlying physical cause of their illness. For others, however, the diagnosis can be upsetting because of the stigma that can be associated with psychiatric conditions.
Understanding that PNES is a complex reaction to stressful situations and not a conscious act is consequently very important.
Anti-epileptic drugs (AEDs) will not resolve PNES, but treatment for PNES may include psychological therapy and/or medication.
Reference:
International League Against Epilepsy (ILAE) website last updated 30 March 2020
Epilepsy Foundation Australia August Website 2021
Fisher et al, (2017) Instruction manual for the ILAE 2017 operational classification of seizure types Epilepsia, 58(4):531–542 http://doi.org/10.1111/epi.13671
Scheffer et al. ‘ILAE classification of the epilepsies: Position paper of the ILAE Commission for Classification and Terminology’ Epilepsia, 58(4):512–521, 2017 http://doi.org/10.1111/epi.13709