A seizure is a sudden change in behavior characterized by changes in sensory perception (sense of feeling) or motor activity (movement) due to an abnormal firing of nerve cells in the brain . Epilepsy is a condition characterized by recurrent seizures that may include repetitive muscle jerking called convulsions.
Seizure disorders and their classification date back to the earliest medical literature accounts in history. In 1964, the Commission on Classification and Terminology of the International League Against Epilepsy (ILAE) devised the first official classification of
seizures, which was revised in 1981 and again in 1989. They then proposed to use a diagnostic scheme of five diagnostic levels or axes, rather than a classification scheme, for characterizing seizures. These axes are (1) the events that occur during the seizure; (2) the type of seizure, chosen from a list that can include where the seizure localizes in the brain and what stimulates it; (3) the type of epileptic syndrome most closely associated with the seizure; (4) the underlying medical or other causes of the syndrome; and (5) the level of impairment the seizure causes. These are proposed recommendations that are still under discussion.
The ILAE classification, meanwhile, is accepted worldwide and is based on electroencephalographic (EEG) studies. Based on this system, seizures can be classified as either focal or generalized. Each of these categories can also be further subdivided.
A focal (partial) seizure develops when a limited, confined population of nerve cells fire their impulses abnormally on one hemisphere of the brain. (The brain has two portions or cerebral hemispheres—the right and left hemispheres.) Focal seizures are divided into simple or complex based on the level of consciousness (wakefulness) during an attack. Simple partial seizures occur in patients who are conscious, whereas complex partial seizures demonstrate impaired levels of consciousness.
A generalized seizure results from initial abnormal firing of brain nerve cells throughout both the left
and right hemispheres. Generalized seizures can be classified as follows:
- tonic-clonic seizures: This is the most common type among all age groups and is categorized into several phases beginning with vague symptoms that appear hours or days before an attack. These seizures are sometimes called grand mal seizures.
- tonic seizures: These are typically characterized by a sustained nonvibratory contraction of muscles in the legs and arms. Consciousness is also impaired during these episodes.
- atonic seizures (also called “drop attacks”): These are characterized by sudden, limp posture and a brief period of unconsciousness, and last for one to two seconds.
- clonic seizures: These are characterized by a rapid loss of consciousness with loss of muscle tone, tonic spasm, and jerks. The muscles become rigid for about 30 seconds during the tonic phase of the seizure and alternately contract and relax during the clonic phase, which lasts 30-60 seconds.
- absence seizures: These are subdivided into typical and atypical forms based on duration of attack and level of consciousness. Absence (petit mal) seizures generally begin at about the age of four and stop by the time the child becomes an adolescent. They usually begin with a brief loss of consciousness and last 1-10 seconds. People having petit mal seizures become very quiet and may blink, stare blankly, roll their eyes, or move their lips. A petit mal seizure lasts 15-20 seconds. When it ends, individuals resume whatever they were doing before the seizure began, will not remember the seizure, and may not realize that anything unusual happened. Untreated, petit mal seizures can recur as many as 100 times a day and may progress to grand mal seizures.
- myoclonic seizures: These are characterized by rapid muscular contractions accompanied with jerks in facial and pelvic muscles.
Subcategories are commonly diagnosed based on electroencephalographic (EEG) results. Terminology for classification in infants and newborns is still controversial.
Simple partial seizures can be caused by congenital abnormalities (abnormalities present at birth), tumor growths, head trauma, stroke , and infections in the brain or nearby structures. Generalized tonic-clonic seizures are associated with drug and alcohol abuse , and low levels of blood glucose (blood sugar) and sodium. Certain psychiatric medications, antihist-amines, and even antibiotics can precipitate tonic-clonic seizures. Absence seizures are implicated with an abnormal imbalance of certain chemicals in the brain that modulate nerve cell activity (one of these neurotransmitters is called gamma-aminobutyric acid or GABA, which functions as an inhibitor). Myoclonic seizures are commonly diagnosed in newborns and children.
Symptoms for the different types of seizures are specific.
SIMPLE PARTIAL SEIZURES
Multiple signs and symptoms may be present during a single simple partial seizure. These symptoms include specific muscles tensing and then alternately contracting and relaxing, speech arrest, vocalizations, and involuntary turning of the eyes or head. There could be changes in vision, hearing, balance, taste, and smell. Additionally, patients with simple partial seizures may have a sensation in the abdomen, sweating, paleness, flushing, hair follicles standing up (piloerection), and dilated pupils (the dark center in the eye enlarges). Seizures with psychological symptoms include thinking disturbances and hallucinations , or illusions of memory, sound, sight, time, and self-image.
COMPLEX PARTIAL SEIZURES
Complex partial seizures often begin with a motionless stare or arrest of activity; this is followed by a series of involuntary movements, speech disturbances, and eye movements.
Generalized seizures have a more complex set of signs and symptoms.
Tonic-clonic seizures usually have vague prodromal (pre-attack) symptoms that can start hours or days before a seizure. These symptoms include anxiety , mood changes, irritability, weakness, dizziness, lightheadedness, and changes in appetite. The tonic phases may be preceded with brief (lasting only a few seconds in duration) muscle contractions on both sides of affected muscle groups. The tonic phase typically begins with a brief flexing of trunk muscles, upward movement of the eyes, and pupil dilation. Patients usually emit a characteristic vocalization. This sound is caused by contraction of trunk muscles that forces air from the lungs across spasmodic (abnormally tensed) throat muscles. This
is followed by a very short period (10–15 seconds) of general muscle relaxation. The clonic phase consists of muscular contractions with alternating periods of no movements (muscle atonia) that gradually increase duration until abnormal muscular contractions stop. Tonic-clonic seizures end in a final generalized spasm. The affected person can lose consciousness during tonic and clonic phases of seizure.
Tonic-clonic seizures can also produce chemical changes in the body. Patients commonly experience lowered carbon dioxide (hypocarbia) due to breathing alterations, increased blood glucose (blood sugar), and an elevated level of a hormone called prolactin. Once affected people regain consciousness, they are usually weak, and have a headache and muscle pain. Tonic-clonic seizures can cause serious medical problems such as trauma to the head and mouth, fractures in the spinal column, pulmonary edema (water in the lungs), aspiration pneumonia (a pneumonia caused by a foreign body being lodged in the lungs), and sudden death. Attacks are generally one minute in duration.
Tonic and atonic seizures have distinct differences but are often present in the same patient. Tonic seizures are characterized by nonvibra-tory muscle contractions, usually involving flexing of arms and relaxing or flexing of legs. The seizure usually lasts less than 10 seconds but may be as long as one minute. Tonic seizures are usually abrupt and patients lose consciousness. Tonic seizures commonly occur during nonrapid eye movement (nonREM) sleep and drowsiness. Tonic seizures that occur during wakeful states commonly produce physical injuries due to abrupt, unexpected falls.
Atonic seizures, also called “drop attacks,” are abrupt, with loss of muscle tone lasting one to two seconds, but with rapid recovery. Consciousness is usually impaired. The rapid loss of muscular tone could be limited to head and neck muscles, resulting in head drop, or it may be more extensive involving muscles for balance, causing unexpected falls with physical injury.
Generalized clonic seizures are rare and seen typically in children with elevated fever. These seizures are characterized by a rapid loss of consciousness, decreased muscle tone, and a generalized spasm that is followed by jerky movements.
Absence seizures are classified as either typical or atypical. The typical absence seizure is characterized by unresponsiveness and behavioral arrest, abnormal muscular movements of the face and eyelids, and lasts less than 10 seconds. In atypical absence seizures, the affected person is generally more conscious, the seizures begin and end more gradually, and do not exceed 10 seconds in duration.
People with myoclonic seizures commonly exhibit rapid muscular contractions. Myoclonic seizures are seen in newborns and children who have either symptomatic or idiopathic (cause is unknown) epilepsy.
Epilepsy and seizures affect a reported 3 million— or 1%—of Americans of all ages, although up to 10% of the population may experience at least one seizure during their lives; some of these events are febrile convulsions associated with high fevers in childhood. Every year, about 200,000 new cases are diagnosed and about 300,000 people have their first convulsion. The annual costs of treatment for seizure and epilepsy, in direct and indirect costs, is about $12.5 billion. Men are slightly more likely than women to develop epilepsy, and its prevalence is higher among minority populations in the United States.
Seizures caused by fever have a recurrence rate of 51% if the attack occurred in the first year of life, whereas recurrence rate is decreased to 25% if the seizure took place during the second year. Approximately 88% of children who experience seizures caused by fever in the first two years experience recurrence.
About 45 million people worldwide are affected by epilepsy. The incidence is highest among young children (under age 2) and the elderly (over age 65). High-risk groups include people with a previous history of brain injury or lesions, children with mental retardation , cerebral palsy, or both, patients with Alzheimer’s disease or stroke, and children with at least one parent who has epilepsy.
Patients seeking help for seizures should first undergo an EEG that records brain-wave patterns emitted between nerve cells. Electrodes are placed on the head, sometimes for 24 hours, to monitor brainwave activity and detect both normal and abnormal impulses. Imaging studies such as magnetic resonance imaging (MRI) and computerized axial tomography (CAT)—that take still “pictures”—are useful in detecting abnormalities in the temporal lobes (parts of the brain associated with hearing) or for helping diagnose tonic-clonic seizures. A complete blood count (CBC) can be helpful in determining whether a seizure is caused by a neurological infection, which is typically accompanied by high fever. If drugs or toxins
in the blood are suspected to be the cause of the seizure(s), blood and urine screening tests for these compounds may be necessary.
Antiseizure medication can be altered by many commonly used medications such as sulfa drugs, erythromycin, warfarin, and cimetidine. Pregnancy may also decrease serum concentration of antiseizure medications; therefore, frequent monitoring and dose adjustments are vital to maintain appropriate blood concentrations of the antiseizure medication—known as the therapeutic blood concentration. Some medications taken during pregnancy could affect the fetus, and women must discuss with their doctors the costs and benefits of any medication taken during pregnancy.
Diagnosis requires a detailed and accurate history, and a physical examination is important because this may help identify neurological or systemic causes. In cases in which a central nervous system (CNS) infection (i.e., meningitis or encephalitis) is suspected, a lumbar puncture (or spinal tap) can help detect an increase in immune cells (white blood cells) that develop to fight the specific infection. (A lumbar puncture involves removing a small amount of cerebrospi-nal fluid—the fluid that bathes and nourishes the brain and spinal cord—from the spinal chord by syringe.)
Treatment is targeted primarily to:
- assist the patient in adjusting psychologically to the diagnosis and in maintaining as normal a lifestyle as possible.
- reduce or eliminate seizure occurrence.
- avoid side effects of long-term drug treatment.
Simple and complex partial seizures respond to drugs such as carbamazepine , valproic acid (valproate), phenytoin, gabapentin , tiagabine, lamotrigine , and topiramate. Tonic-clonic seizures tend to respond to valproate, carbamazepine, phenytoin, and lamotrigine. Absence seizures seem to be sensitive to ethosuximide, valproate, and lamotrigine. Myoclonic seizures can be treated with valproate and clonazepam . Tonic seizures seem to respond favorably to valproate, felbamate, and clonazepam.
People treated with a class of medications called barbiturates (Mysoline, Mebral, phenobarbital) have adverse cognitive (thinking) effects. These cognitive effects can include decreased general intelligence, attention, memory, problem solving, motor speed, and visual motor functions. The drug phenytoin (Dilantin) can adversely affect speed of response, memory, and attention. Other medications used for treatment of seizures do not have substantial cognitive impairment.
Surgical treatment may be considered when medications fail. Advances in medical sciences and techniques have improved methods of identifying the parts of the brain that generate abnormal discharge of nerve impulses. The most common type of surgery is the extratemporal cortical resection. In this procedure, a small part of the brain responsible for causing the seizures is removed. An option of last resort for people with extreme, uncontrollable seizures is functional hemispherectomy, in which communication between the two hemispheres of the brain is severed. Surgical intervention may be considered a feasible treatment option if:
- the site of seizures is identifiable and localized.
- surgery can remove the seizure-generating (epileptogenic) area.
- surgical procedure will not cause damage to nearby areas.
Another treatment approach that has been found to reduce seizures in some children is the ketogenic diet. This diet reduces available glucose in the body, forcing the child’s body to turn to fat stores for energy. It is a high-fat diet that results in the person getting about 80% of their calories from fat. No one is exactly sure why this diet, which mimics starvation in the body, works to prevent seizures. It also does not work for every child, and the reasons for that also are unclear.
About 30% of patients with severe seizures (starting in early childhood), continue to have attacks and usually never achieve a remission state. In the United States, the prevalence of treatment-resistant seizures is about one to two per 1,000 people. About 60-70% of people achieve a five-year remission within 10 years of initial diagnosis. Approximately half of these patients become seizure-free. Usually the prognosis is better if seizures can be controlled by one medication, the frequency of seizures decreases, and there is a normal EEG and neurological examination prior to medication cessation.
People affected by seizures have increased death rates compared with the general population. Patients who have seizures of unknown cause have an increased chance of dying due to accidents (primarily drowning). Other causes of seizure-associated death
Electroencephalograph (EEG) —An instrument that measures the electrical activity of the brain. The EEG traces the electrical activity in the form of wave patterns onto recording paper. Wave patterns that have sudden spikes or sharp waves strongly suggest seizures. An EEG with a seizure-type wave pattern is called an epileptiform EEG.
Hallucination —False sensory perceptions. A person experiencing a hallucination may “hear” sounds or “see” people or objects that are not really present. Hallucinations can also affect the senses of smell, touch, and taste.
Illusion —A misperception or misinterpretation in the presence of a real external stimulus.
include abnormal heart rhythms, water in the lungs, or heart attack.
There are no gold-standard recommendations for prevention because seizures can be caused by genetic factors, blood abnormalities, many medications, illicit drugs, infection, neurologic conditions, and other systemic diseases. If a person has had a previous attack or has a genetic propensity, care is advised when receiving medical treatment or if diagnosed with an illness correlated with possible seizure development.
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Epilepsy Foundation. 4351 Garden City Drive, Landover, MD 20785-7223. Telephone: (800) 332-1000. Web site: http://www.efa.org/
International League Against Epilepsy. “Overview of classification and other information.” Available online at: http://www.ilae-epilepsy.org/Visitors/Centre/ctf/overview.cfm
Laith Farid Gulli, MD
Alfredo Mori, MD, FACEM
Emily Jane Willingham, PhD