Types of Seizures
What is a seizure?
A seizure is a burst of uncontrolled electrical activity between brain cells (also called neurons or nerve cells) that causes temporary abnormalities in muscle tone or movements (stiffness, twitching or limpness), behaviors, sensations or states of awareness.
Seizures are not all alike. A seizure can be a single event due to an acute cause, such as medication. When a person has recurring seizures, this is known as epilepsy.
- Seizures symptoms vary and can include a sudden change in awareness or full loss of consciousness, unusual sensations or thoughts, involuntary twitching or stiffness in the body or severe stiffening and limb shaking with loss of consciousness (a convulsion.)
- There are two major classes or groups of seizures: focal onset and generalized onset.
- Focal onset seizures start in one area and can spread across the brain and cause mild or severe symptoms, depending on how the electrical discharges spread.
- Generalized seizures can start as focal seizures that spread to both sides of the brain. They also can occur as “generalized onset” seizures in which seizure activity start simultaneously over both sides of the brain. Generalized onset seizures usually start during childhood and are similar to a thermostat surge or a light flash — abnormal regulation between parts of the brain of causes the seizures.
- Seizures of all kinds are most commonly treated with medication, and, if they are difficult to control, with diet therapy, nerve stimulation or surgery.
It is important for the doctor to get an accurate seizure diagnosis in order to implement the most appropriate kind of treatment. Focal and generalized onset seizures usually have different causes and accurately diagnosing seizure types often helps identify the cause for the seizures.
Whether or not the doctor can determine the cause for an individual’s seizures, treatment will likely mean medication. Seizures that are difficult to control may be improved with nerve stimulation or diet therapy. Patients whose seizures are due to a focal scar or other lesion in the brain may be good candidates for epilepsy surgery.
Focal, or Partial Seizures
Focal seizures are also called partial seizures since they begin in one area of the brain. They can be caused by any type of focal injury that leaves scar tangles. A medical history or MRI will identify a cause (such as trauma, stroke or meningitis) in about half of the people who have focal seizures. Developmental scars — ones that occur as part of fetal and early growth of the brain — are common causes of focal seizures in children.
Focal Seizures: What Happens
Focal seizures can start in one part of the brain and spread to other areas, causing symptoms that are mild or severe, depending on how much of the brain becomes involved.
At first, the person may notice minor symptoms, which is referred to as an aura. The person may have altered feelings or sense that something is about to happen (premonition). Some people experiencing an aura describe a rising sensation in the stomach similar to riding on a roller coaster.
As the seizure spreads across the brain, more symptoms appear. If the abnormal electrical activity involves a large area of the brain, the person may feel confused or dazed, or experience minor shaking, muscle stiffening, or fumbling or chewing motions. Focal seizures that cause altered awareness are called focal unaware seizures or complex partial seizures.
The electrical activity of the seizure can remain in one sensory or motor area of the brain, resulting in a focal aware seizure (also called simple partial seizure). The person is aware of what is happening, and may notice unusual sensations and movements.
Focal seizures can evolve into major events that spread to the entire brain and cause tonic clonic seizures. These seizures are important to treat and prevent since they can cause respiratory problems and injuries.
Generalized-onset seizures are surges of abnormal nerve discharges throughout the cortex of the brain more or less at the same time. The most common cause is an imbalance in the “brakes” (inhibitory circuits) and “accelerator” (excitatory circuits) of electrical activity in the brain.
Generalized-onset Seizures: Genetic Considerations
Generalized seizures may have a genetic component, but only a small number of people with generalized seizures have family members with the same condition. There is a slight increase in risk for generalized seizures in the children or other family members of an affected person with generalized seizures, but the severity of the seizures can vary from person to person. Genetic testing may reveal a cause for generalized seizures.
Sleep deprivation or drinking large amounts of alcohol can increase the excitatory response and increase the risk of generalized-onset seizures, especially in people with a genetic tendency to have them.
Types of Generalized-Onset Seizures
Absence Seizures (“Petit Mal Seizures”)
Childhood absence epilepsy shows up as brief staring episodes in children, usually starting between ages four and six. Children usually outgrow these. Juvenile absence epilepsy starts slightly later and can persist into adulthood; people with these kinds of seizures may develop tonic-clonic seizures in addition to absence seizures in adulthood.
Myoclonic seizures consist of sudden body or limb jerks that can involve the arms, head and neck. The spasms occur on both sides of the body in clusters, especially in the morning. When these seizures develop in adolescence along with tonic-clonic seizures, they are part of a syndrome called juvenile myoclonic epilepsy. People can also have myoclonic seizures as part of other epilepsy related-conditions.
Tonic and Atonic Seizures (“Drop Attacks”)
Some people, usually those with multiple brain injuries and intellectual disability, have tonic seizures consisting of sudden stiffness in the arms and body, which can cause falls and injuries. Many persons with tonic seizures have a syndrome called Lennox Gastaut syndrome. This condition may involve intellectual disability, multiple seizure types including tonic seizures. People with Lennox Gastaut syndrome can have a distinctive EEG pattern called slow spike and wave.
Persons with diffuse brain disorders also may have atonic seizures, characterized by a sudden loss of body tone that results in collapsing, often with injuries. A sequence of a brief tonic episode followed by an atonic seizure is called a tonic-atonic seizure. Tonic and atonic seizures are often managed with specific medications and sometimes with nerve stimulation and diet therapies.
Tonic, Clonic and Tonic-Clonic (Formerly called Grand Mal) Seizures
Tonic clonic seizures can evolve from any of the focal or generalized seizure types. For example, a focal seizure can spread to both sides of the brain and cause tonic-clonic seizures. A cluster of myoclonic seizures can become continuous and evolve into a tonic-clonic seizure. Generalized onset tonic-clonic seizures can occur alone or as part of another syndrome such as juvenile myoclonic epilepsy (JME) or juvenile absence epilepsy during adulthood.