A seizure is a sudden change in the brain's normal electrical activity. During a seizure, brain cells "fire" uncontrollably at up to four times their normal rate, temporarily affecting the way a person behaves, moves, thinks or feels.
There are two major types of seizures:
- Primary generalized seizures – The seizure affects the entire cerebral cortex, the outer portion of the brain that contains the majority of brain cells. In this type of seizure, the abnormal firing of brain cells occurs on both sides of the brain at about the same time.
Partial (focal) seizure – The abnormal firing of brain cells begins in one region of the brain and remains in that one region.
Many conditions can affect the brain and trigger a seizure, including:
- Brain injury, either before or after birth
- Infections, especially meningitis and encephalitis
- Eating or drinking toxic substances
- Metabolic problems
- High fever (in children)
- Genetic conditions, including tuberous sclerosis
- Structural abnormalities in the brain's blood vessels
Seizures are common. A person may have only one seizure without a recurrence. Epilepsy is a condition in which seizures continue to recur.
Symptoms
Primary Generalized Seizures
The different types of primary generalized seizures cause different symptoms:
- Generalized tonic-clonic seizure (also called grand mal seizure) – In this type of seizure, the person usually loses consciousness and falls to the ground. All body muscles can contract at once in a sustained contraction, or they can contract in a series of shorter rhythmic contractions, or both. Some patients also lose bowel or bladder control. The seizure episode typically lasts for less than a minute and is followed by period of lethargy (sluggishness) and temporary confusion. Often muscles are very sore after a generalized seizure.
- Absence seizure (also called petit mal seizure) – In this type of seizure, loss of consciousness is so brief that the person usually doesn't change position. For a few seconds, the person may have a blank stare or rapid blinking. This type of seizure usually begins in childhood or early adolescence.
- Status epilepticus – A state of a prolonged seizure (20 minutes or longer) or a series of seizures without fully regaining consciousness. This is a life-threatening medical emergency.
Partial (Focal) Seizures
The different types of partial seizures cause different symptoms:
- Simple partial seizure – In a simple partial seizure, the seizure-related electrical discharges remain localized so that the person experiences a feeling, sensation, movement or other symptom without losing consciousness. During a simple partial seizure, the person remains awake and aware. Symptoms vary depending on the specific brain area involved and may include:
- Jerking movements in one part of the body
- An experience of abnormal smells or a distorted environment
- Unexplained fear or rage
Complex partial seizure – This is the most common type of partial seizure. In this type of seizure, the person loses awareness of his or her surroundings and is unresponsive or only partially responsive. There may be a blank stare, chewing or lip-smacking, or repetitive movements of the hands. After the seizure, the person typically is confused and has no memory of the episode.
Either type of partial seizure may become a generalized seizure if the electrical activity spreads from the part of the brain where the seizure started to the rest of the cerebral cortex.
Seizures often are followed by a period of lethargy, drowsiness and confusion. This happens most often with generalized seizures. These symptoms are not part of the seizure itself but are connected to the brain recovering from the effects of the seizure. In addition, warning symptoms called an aura may occur immediately before complex partial and generalized seizures. The aura is actually a brief simple partial seizure that generally involves changes in visual perception, smell, taste or emotional state.
Diagnosis
It's unlikely that you will have seizure symptoms while you are in a doctor's office or emergency department. For this reason, it is important to ask anyone who witnessed your seizure to describe the event and to write it down for your doctor. This description can help your doctor determine the type of seizure you had.
The diagnosis is based primarily on your symptoms that are described. Usually, the physical exam and neurological examination are normal between spells. An adult who experiences a seizure for the first time will be evaluated with a head scan and blood tests to look for chemical imbalances. Your doctor will order either computed tomography (CT) or magnetic resonance imaging (MRI) of the brain. Most people with a new diagnosis of seizure undergo an electroencephalogram (EEG), which monitors and records brain waves from a series of electrodes placed on the scalp. Specific abnormalities in brain wave patterns can help your doctor to determine what kind of seizure you may have. The EEG is a brief outpatient procedure.
