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 again in 1981. This classification 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 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 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 between one and 10 seconds. People having a petit mal seizure 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, the individual resumes whatever he or she was 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 EEG results. Terminology for classification in infants and newborns is still controversial.
Causes and symptoms
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, antihistamines, 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 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. 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) of gradually increasing 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 elevated level of a hormone called prolactin. Once the affected person regains consciousness, he or she is usually weak, and has 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 SEIZURES. Tonic and atonic seizures have distinct differences but are often present in the same patient. Tonic seizures are characterized by nonvibratory 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. 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.
CLONIC SEIZURES. 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 generalized spasm that is followed by jerky movements.
ABSENCE SEIZURES. 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.
MYOCLONIC SEIZURES. 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.
Approximately 1.5 million persons in the United States suffer from a type of seizure disorder. The annual incidence (number of new cases) for all types of seizures is 1.2 per 1,000 and, for recurrent seizures, is 0.54 per 1,000. Isolated seizures may occur in up to 10% of the general population. Approximately 10–20% of all patients have intractable epilepsy (epilepsy that is difficult to manage or treat). It is estimated that 45 million people in the world are affected by seizures. Seizures affect males and females equally and can occur among all age groups. There seems to be a strong genetic correlation, since seizures are three times more prevalent among close relatives than they are in the general population.
Children delivered in the breech position have increased prevalence (3.8%) of seizures when compared to infants delivered in the normal delivery position (2.2%). 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.
Approximately 45 million people worldwide are affected by epilepsy. The incidence is highest among young children and the elderly. High-risk groups include persons with a previous history of brain injury or lesions.
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 brain-wave activity and detect both normal and abnormal impulses. Imaging studies such as magnetic resonance imaging (MRI) and computed 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. Diagnosis requires a detailed and accurate history, and a physical examination is important since 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 is removing from the spinal chord, by syringe, of a small amount of cerebrospinal fluid—the fluid that bathes and nourishes the brain and spinal cord.)
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. Surgical treatment now accounts for about 5,000 procedures annually. The most common type of surgery is the focal cortical resection. In this procedure, a small part of the brain responsible for causing the seizures is removed. 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
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 persons. About 60–70% of persons 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 seizure 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 include abnormal heart rhythms, water in the lungs, or heart attack.
There are no gold standard recommendations for prevention, since 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.
See also ; ; ; Substance abuse and related disorders
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Epilepsy Foundation. 4351 Garden City Drive, Landover, MD 20785-7223. Phone: (800) 332-1000. Web site: <http://www.efa.org/> .
Laith Farid Gulli, M.D.
Alfredo Mori, M.D., FACEM