Seizures look very different in different people, depending on the location of the seizure in the brain. In general, seizures are classified as focal or generalized, depending on whether they begin in part of the brain or in the whole brain at once.
Seizures may be subtle or dramatic. A child with absence seizures can simply look like they are daydreaming or "spacing out" for a couple of seconds with no apparent movements whatsoever. A child with focal seizures may hear a sound that isn’t there or may twitch in just one arm. A child with generalized or focal to bilateral tonic-clonic seizures will fall to the floor and convulse. A child having a seizure may lose awareness, or they may be aware of their surroundings and able to talk.
Seizure classification
Seizures are classified as focal or generalized based on whether they begin in part of the brain or in the whole brain at once, with further separation based on level of awareness, motor symptoms, and any other seizure-related symptoms.
Generalized seizures seem to begin in the whole brain at the same time. They include the following.
- Absence seizures, in which the child briefly stares, sometimes with subtle repetitive eye blinking, and does not hear or see what is happening around them.
- Myoclonic seizures, in which the child has twitches or jerks in all or part of their body, usually upon awakening (it is common and normal to have brief body jerks when falling asleep or while sleeping. These types of jerks are not seizures.).
- Atonic seizures, in which the child goes limp and falls.
- Tonic seizures, in which the child goes stiff.
- Clonic seizures, in which the child jerks rhythmically.
- Tonic-clonic seizures, in which the child goes rigid, then shakes or jerks rhythmically.
Focal seizures begin in only one part of the brain. They may remain there and cause only symptoms related to that area of the brain, or they can become generalized (that is, they may spread out to involve the whole brain). They include the following.
- Focal aware seizures, in which the child is still aware of what is happening around them; these may have motor, somatosensory (e.g. numbness, tingling), autonomic (e.g., increased heart rate, flushing of the face), or cognitive (e.g., loss of speech, hallucinations) symptoms.
- Focal seizures with impaired awareness.
- Both focal aware and impaired awareness seizures may or may not present with motor symptoms.
Finally, some seizures may be unclassified because the health-care provider does not have enough information about what type of seizures they are. With babies, for instance, it may be difficult to tell exactly what type of seizure the baby is having, whether the seizure is focal or generalized, or where it began, because babies’ brains are not yet developed enough to show the clues that appear in older children and adults. Health-care providers cannot ask babies what they remember about the seizure and may not be able to tell whether they lost awareness during the seizure. Seizures in babies are called neonatal seizures.
Status epilepticus
Status epilepticus occurs when a seizure continues for a long time (more than half an hour), or when a child has several seizures without time to recover between them. It can happen with any seizure type.
Seizures in special situations
Not all seizures are caused by epilepsy. Seizures can be provoked by a head injury, lack of oxygen to the brain, a high fever, an infection such as meningitis, drugs, withdrawal from medication or high blood sugar. These are called provoked seizures. Children who have many provoked seizures may develop epilepsy over time.
Febrile seizures are provoked by fever and are the most common type of provoked seizures in childhood. They usually occur in children between six months and five years of age. About two to five per cent of children will have a febrile seizure before they turn five years old.
What do different types of seizures indicate?
Different seizure types often indicate different causes or syndromes. For instance, brain injury is more likely to cause focal seizures, while many epilepsy syndromes without a known cause produce generalized seizures. Generalized epilepsy syndromes without a known cause usually have an underlying genetic cause, with a tendency to recur in some families.
Different seizure types may also be treated differently and have different prognoses. Different medications are used to treat focal seizures as compared to generalized seizures. Also, children with drug resistant focal seizures often need epilepsy surgery.
Nearly 75 per cent of children with epilepsy have more than one type of seizure. For example, children with juvenile myoclonic epilepsy often have both myoclonic and generalized tonic-clonic seizures at different times.
One seizure may progress to a different type of seizure; for instance, focal seizures may become generalized, or a myoclonic seizure may progress to a generalized tonic-clonic seizure.