seizure
seizure, sudden, uncontrolled electrical activity in the brain. Seizures produce a wide range of symptoms, including changes in behaviour, shaking or sudden movements, and changes in consciousness. Often the cause of a seizure is unknown.
Characteristics
About 25 to 30 percent of seizures are provoked seizures (also known as acute symptomatic seizures), being triggered by underlying conditions, such as fever or stroke, or by exposure to flashing lights or moving objects. Unprovoked seizures occur in the absence of any clear cause; in some cases, they happen days after a possible cause, such as a head injury or alcohol withdrawal. Seizures can be a onetime event—some 10 percent of people worldwide experience a single seizure in their lifetime—or a recurring event. Recurrent seizures typically are a sign of epilepsy, a chronic neurological disorder caused by an absence or excess of signaling of neurons in the brain; epilepsy affects more than 50 million people worldwide.
The duration of a seizure varies, some lasting 30 seconds and others lasting two minutes. A seizure that is more than five minutes in duration or having more than one seizure that occurs over that same amount of time, with no return to consciousness between episodes, is known as status epilepticus. Status epilepticus can result in brain damage or death.
Types of seizures
Seizures are categorized into two broad types: focal (partial) or generalized. Both types of seizures may be preceded by a prodrome, or an early warning symptom, in which the individual experiences an altered emotion or sensation. A prodrome may include an aura, with distortions in vision (e.g., seeing bright lights), hearing strange sounds, changes in taste or smell, feeling strange sensations on the skin, or experiencing a sense of déjà vu or unexplained emotions, such as fear or joy. The person may also sweat, drool, become pale, or experience a change in heart rate. Difficulty speaking or involuntary twitching may also occur.
Focal seizures
Focal seizures—which can be caused by prior injury to the brain, such as from stroke, meningitis, or physical trauma—begin in the left or right hemisphere and remain in that area; thus, symptoms occur in a specific part or on one side of the body. Focal seizures may be characterized as simple partial seizures when the electrical discharges do not spread and the affected person experiences only an aura. This is in contrast to a complex partial seizure, wherein the electrical discharges spread, resulting in a loss of or altered consciousness. Affected individuals may feel like they are dreaming and may stare into space and perform repetitive movements, such as walking in circles or rubbing their hands. Afterward they may not know that the seizure occurred.
Generalized seizures
Generalized seizures occur when electrical discharges of a focal seizure spread to both hemispheres of the brain. Generalized seizures may also have generalized onset, meaning that they begin on both sides of the brain simultaneously. There are several different types of generalized seizures.
- Absence seizures (or petit mal seizures) are brief, lasting about 5–10 seconds, and may happen dozens or hundreds of times per day; they often occur in children.
- Atonic seizures (also known as drop attacks) last about 15 seconds and involve a loss of muscle control, causing the affected individual to collapse.
- Clonic seizures involve repetitive or rhythmic jerking movements, particularly of the neck, face, and arms, on both sides of the body.
- Myoclonic seizures are characterized by sudden brief jerks or twitching movements and occur especially in the morning.
- Tonic seizures cause muscle stiffening in the arms, legs, and back and sometimes cause the individual to lose consciousness and fall.
- Tonic-clonic seizures (or grand mal seizures) are often seen in epilepsy but can also be caused by other conditions (e.g., brain injury, infection, congenital or development abnormalities, or drug or alcohol withdrawal). Tonic-clonic seizures may be several minutes in duration and involve a tonic phase, which lasts 10–30 seconds and frequently is characterized by screaming and an abrupt loss of consciousness, and a clonic phase, which lasts 30–60 seconds or longer and is characterized by convulsions.
- Tonic-atonic seizures involve a tonic episode followed by an atonic episode.
Causes
Seizures may be caused by genetic disorders or congenital abnormalities, such as abnormalities of blood vessels in the brain. Acquired conditions and injuries associated with seizures include stroke, severe concussion, traumatic brain injury, degenerative brain diseases (e.g., Alzheimer disease or frontotemporal dementia), infection, and lack of sleep. Flashing lights, moving patterns, and certain medications also can trigger a seizure in some persons. Some seizures are related to drug use, including alcohol intoxication and alcohol withdrawal. High fever can cause febrile seizures; this is especially common in children between six months and five years of age.
Diagnosis and treatment
Seizure disorders may be diagnosed based on medical history, symptoms, and various tests, including electroencephalogram (EEG), computed tomography (CT), magnetic resonance imaging (MRI), spinal tap, and blood testing. Treatment varies widely and is based on treating the underlying cause. If the cause cannot be identified or treated, antiepileptic drugs may be prescribed. Some patients also benefit from a ketogenic diet (a low-carbohydrate, high-protein diet). Surgery may be undertaken in cases in which scarred brain tissue is suspected of triggering seizures. Vagus nerve stimulation, in which an implanted device sends mild electrical pulses to the brain via the vagus nerve to stabilize electrical activity in the brain, may be used to prevent or reduce the frequency of seizures.