Epilepsy Program: Seizure types
A seizure is a temporary disruption of brain function due to abnormal, excessive activity in the nerve cells in the brain. It’s caused by an imbalance of brain chemicals called neurotransmitters.
Seizures can be provoked, which means they are caused by sudden alternations in nerve cell activity, or unprovoked, which means the seizure has genetic causes or is the result of an acquired brain disorder or injury.
Seizures also may be triggered by infection, drug use, metabolic changes in the body (such as hypoglycemia), ingestion of toxins or medical problems such as eclampsia.
Seizures usually fall into one of two categories: focal or generalized.
Focal seizures are also called partial seizures because they occur in one part of brain. About 60 percent of people with epilepsy have focal seizures.
These seizures are often further defined by the specific part of the brain in which they originate, such as:
- Temporal lobe — About 73 percent of people with epilepsy have the temporal lobe subset of the disorder.
- Frontal lobe — About 20 percent of patients have this form of the disorder.
- Posterior quadrant — Fewer than 10 percent of people with epilepsy have this subset.
During a focal seizure, a person may be aware of what’s happening or their awareness can be impaired.
Typically, a person having a focal seizure remains conscious and often experiences other symptoms. They may feel strong emotions of joy or anger. An individual’s sense of hearing, smell, taste or vision may be temporarily altered. It may feel like one part of the body is moving, such as a hand, although it is not.
Some people, although conscious, report feeling as if they are in dream. The body also can produce repetitious movements, like twitching, blinking, swallowing or walking in a circle. Focal seizures usually last one or two minutes.
Generalized seizures involve the entire brain. These seizures occur because of abnormal brain activity that rapidly emerges on both sides of the brain.
During this kind of seizure, a person loses consciousness and may fall. Strong muscle contractions may occur. There are several types of generalized seizures including:
- Absence seizures — During this type of seizure, which is also known as a petite mal seizure, a person may appear to be staring into space and may have a slight twitching of the muscles.
- Tonic seizures — This type of seizure causes stiffening of muscles, typically in the back, legs and arms.
- Clonic seizures — Clonic seizures usually produce repeated jerking movements of muscles on both sides of the body.
- Myoclonic seizures — This type of seizure is defined by jerking or twitching of the upper body, arms or legs.
- Atonic seizures — Atonic seizures typically produce a temporary loss of normal muscle tone, which often leads the affected person to fall down or drop the head involuntarily.
- Tonic-clonic seizures — Also called a grand mal seizure, this type causes a combination of symptoms, including stiffening of the body and repeated jerking of the limbs and a loss of consciousness.
Unknown onset seizures
Sometimes, seizures cannot be clearly defined as either focal or generalized. For example, some people have seizures that originate as a focal seizure then spread to the entire brain. Your seizures may be initially diagnosed as unknown onset but reclassified later as focal or generalized, after your doctor learns more about your condition.
Classification by cause
You may also hear other terms that describe seizures. For example, sometimes seizures are classified by the cause, including:
- Symptomatic — Also called structural or metabolic seizures, this term means that the cause is unknown and is not genetic.
- Idiopathic — This term means genetic factors are involved.
- Cryptogenic — This means the cause is unknown.
For more information about the UC Irvine Health Comprehensive Epilepsy Program or to schedule an appointment, call 714-456-6203 or request an appointment online.