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|Classification and external resources|
Generalized 3 Hz spike and wave discharges in EEG
|ICD-10||G40, P90, R56|
|Classification and external resources|
Generalized 3 Hz spike and wave discharges in EEG
|ICD-10||G40, P90, R56|
An epileptic seizure (colloquially a fit) is a brief episode of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. The outward effect can vary from uncontrolled jerking movement (tonic-clonic seizure) to as subtle as a momentary loss of awareness (absence seizure). The disease of the brain characterized by an enduring predisposition to generate epileptic seizures is called epilepsy, but seizures can also occur in people who do not have epilepsy. Additionally, there are a number of conditions that look like epileptic seizures but are not.
5–10% of people who live to 80 years old have at least one epileptic seizure and the chance of experiencing a second seizure is between 40% and 50%. About 50% of patients with an unprovoked apparent “first seizure” have had other minor seizures, so their diagnosis is epilepsy. Epilepsy affects about 1% of the population currently and affects about 4% of the population at some point in time. Most of those affected—nearly 80%—live in developing countries.
The signs and symptoms of seizures vary depending on the type. The most common type of seizures are convulsive (60%). Two-thirds of these begin as focal seizures and become generalized while one third begin as generalized seizures. The remaining 40% of seizures are non-convulsive, an example of which is absence seizures.
Jerking activity may start in a specific muscle group and spread to surrounding muscle groups in which case it is known as a Jacksonian march. Unusual activities that are not consciously created may occur. These are known as automatisms and include simple activities like smacking of the lips or more complex activities such as attempts to pick something up.
There are six main types of generalized seizures: tonic-clonic, tonic, clonic, myoclonic, absence, and atonic seizures. They all involve a loss of consciousness and typically happen without warning.
A seizure can last from a few seconds to more than five minutes at which point it is known as status epilepticus. Most tonic-clonic seizures last less than two or three minutes. Absence seizures are usually around 10 seconds in duration.
After the active portion of a seizure, there is typically a period of confusion referred to as the postictal period before a normal level of consciousness returns. This usually lasts 3 to 15 minutes but may last for hours. Other common symptoms include: feeling tired, headache, difficulty speaking, and abnormal behavior. Psychosis after a seizure is relatively common, occurring in between 6 and 10% of people. Often people do not remember what occurred during this time.
Seizures have a number of causes. Of those with seizure about 25% have epilepsy. A number of conditions are associated with seizures but are not epilepsy including: most febrile seizures and those that occur around an acute infection, stroke, or toxicity. These seizures are known as "acute symptomatic" or "provoked" seizures and are part of the seizure-related disorders. In many the cause is unknown.
Different causes of seizures are common in certain age groups.
A number of disorders including: low blood sugar, low blood sodium, hyperosmolar nonketotic hyperglycemia, high blood sodium, low blood calcium and high blood urea levels may cause seizures. As may hepatic encephalopathy and the genetic disorder porphyria.
Both medication and drug overdoses can result in seizures, as may certain medication and drug withdrawal. Common drugs involved include: antidepressants, antipsychotics, cocaine, insulin, and the local anaesthetic lidocaine. Difficulties with withdrawal seizures commonly occurs after prolonged alcohol or sedative use.
Seizures may occur as a result of high blood pressure, known as hypertensive encephalopathy, or in pregnancy as eclampsia when accompanied by either seizures or a decreased level of consciousness. Very high body temperatures may also be a cause. Typically this requires a temperature greater than 42 °C (107.6 °F).
Electroconvulsive therapy (ECT) deliberately sets out to induce a seizure for the treatment of major depression.
Normally brain electrical activity is non synchronous. In epileptic seizures, due to problems within the brain, a group of neurons begin firing in an abnormal, excessive, and synchronized manner. This results in a wave of depolarization known as a paroxysmal depolarizing shift.
Normally after an excitatory neuron fires it becomes more resistant to firing for a period of time. This is due in part from the effect of inhibitory neurons, electrical changes within the excitatory neuron, and the negative effects of adenosine. In epilepsy the resistance of excitatory neurons to fire during this period is decreased. This may occur due to changes in ion channels or inhibitory neurons not functioning properly. This then results in a specific area from which seizures may develop, known as a "seizure focus". Another cause of epilepsy may be the up regulation of excitatory circuits or down regulation of inhibitory circuits follow an injury to the brain. These secondary epilepsies, occur through processes known as epileptogenesis. Failure of the blood–brain barrier may also be a causal mechanism.
Focal seizures begin in one hemisphere of the brain while generalized seizures begin in both hemispheres. Some types of seizures may change brain structure, while others appear to have little effect. Gliosis, neuronal loss, and atrophy of specific areas of the brain are linked to epilepsy but it is unclear if epilepsy causes these changes or if these changes result in epilepsy.
It is important to distinguish primary seizures from secondary causes. Depending on the presumed cause blood tests and/or lumbar puncture may be useful. Hypoglycemia may cause seizures and should be ruled out. An electroencephalogram and brain imaging with CT scan or MRI scan is recommended in the work-up of seizures not associated with a fever.
Seizure types are organized by whether the source of the seizure is localized (focal seizures) or distributed (generalized seizures) within the brain. Generalized seizures are divided according to the effect on the body and include tonic-clonic (grand mal), absence (petit mal), myoclonic, clonic, tonic, and atonic seizures. Some seizures such as epileptic spasms are of an unknown type.
Focal seizures (previously known as partial seizures) used to be divided into simple partial or complex partial seizure. This is no longer recommended, and instead it is preferred to describe what has occurred during a seizure.
Most people are in a postictal state following a seizure (drowsy or confused). There may be signs of other injuries. A bite to the side of the tongue is helpful to confirm a seizure when present; however, only a third of those with seizures had such a bite.
An electroencephalography is only recommended in those who likely had an epileptic seizure and may help determine the type of seizure or syndrome present. In children it is typically only needed after a second seizure. It cannot be used to rule out the diagnosis and may be falsely positive in those without the disease. It certain situations it may be useful to prefer the EEG while sleeping or sleep deprived.
Diagnostic imaging by CT scan and MRI is recommended after a first non-febrile seizure to detect structural problems inside the brain. MRI is generally a better imaging test except when intracranial bleeding is suspected. Imaging may be done at a later point in time in those who return to their normal selves while in the emergency room. If a person has a previous diagnosis of epilepsy with previous imaging repeat imaging is not usually needed with subsequent seizures.
In adults testing electrolytes, blood glucose and calcium levels is important to rules these out as causes. As is an electrocardiogram. A lumbar puncture may be useful to diagnose a central nervous system infection but is not routinely needed. Routine antiseizure medical levels in the blood are not required in adults or children. In children additional tests may be required.
A high blood prolactin level within the first 20 minutes following a seizure may be useful to confirm an epileptic seizure as opposed to psychogenic non-epileptic seizure. Serum prolactin level is less useful for detecting partial seizures. If it is normal an epileptic seizure is still possible and a serum prolactin does not separate epileptic seizures from syncope. It is not recommended as a routine part of diagnosis epilepsy.
Differentiating an epileptic seizure from other conditions such as syncope can be difficult. Other possible conditions that can mimic a seizure include: decerebrate posturing, psychogenic seizures, dystonia, migraine headaches, and strychnine poisoning. In addition, 5% of people with a positive tilt table test may have seizure-like activity that seems to be due to cerebral hypoxia. Convulsions may occur do to psychological reasons and this is known as a psychogenic non-epileptic seizure. Non-epileptic seizures may also occur due to a number of other reasons.
In those with a history of febrile seizures medications (both antipyretics and anticonvulsants) have not been found effective for prevention; however, some appear to be associated with harm. In those without a history of seizures and a subdural hematoma the evidence is unclear regarding a benefit versus harm from using anticonvulsants. This is also true following a craniotomy as well as after stroke, intracranial venous thrombosis, and subarachnoid haemorrhage both in those who have and have not had seizures.
Potentially sharp or dangerous objects should also be moved from the vicinity, so that the individual is not hurt. After the seizure if the person is not fully conscious and alert, they should be placed in the recovery position. A seizure longer than five minutes is a medical emergency known as status epilepticus. Contrary to a common misconception, bystanders should not attempt to force objects into the mouth of the person suffering a seizure, as doing so may cause injury to the teeth and gums.
The first line treatment of choice for someone who is actively seizing is a benzodiazepine, most guidelines recommend lorazepam. This may be repeated if there is no effect after 10 minutes. If there is no effect after two doses, barbiturates or propofol may be used.
Ongoing medication is not typically needed after a first seizure and is generally only recommended after a second one has occurred or in those with structural lesions in the brain. After a second seizure anti-epileptic medications are recommended. Approximately 70% of the people are able to get full control with continuous use of medication. Typically one type of anticonvulsant is preferred.
Following a first seizure, the risk of more seizures in the next two years is 40%–50%. The greatest predictors of more seizures are problems either on the electroencephalogram or on imaging of the brain. In adults, after 6 months of being seizure-free after a first seizure, the risk of a subsequent seizure in the next year is less than 20% regardless of treatment. Up to 7% of seizures that present to the emergency department (ER) are in status epilepticus. In those with a status epilepticus, mortality is between 10% and 40%. Those who have a seizure that is provoked (occurring close in time to an acute brain event or toxic exposure) have a low risk of re-occurrence, but have a higher risk of death compared to those with epilepsy.
5–10% of people who live to 80 years old have at least one epileptic seizure and the chance of experiencing a second seizure is between 40% and 50%. About 0.7% in the general population of the United States will present to an emergency department after a seizure in a given year, 7% of them with status epilepticus. Known epilepsy though is an uncommon cause of seizures in the emergency department, accounting for a minority of seizure-related visits. About 50% of patients with an unprovoked apparent “first seizure” have had other minor seizures, so their diagnosis is epilepsy.
Following standardization proposals devised by Henri Gastaut and published in 1970, terms such as "petit mal", "grand mal", "Jacksonian", "psychomotor", and "temporal-lobe seizure" have fallen into disuse.
Seizures result in direct economic costs of about one billion dollars in the United States. Epilepsy results in economic costs in Europe of around 15.5 billion Euros in 2004. In India epilepsy is estimated to result in costs of 1.7 billion USD or 0.5% of the GDP. They make up about 1% of emergency department visits (2% for emergency departments for children) in the United States.
Many areas of the world require there to be a minimum of six months from the last seizure before people can return to driving.
Scientific work into the prediction of epileptic seizures began in the 1970s. Several techniques and methods have been proposed, but evidence regarding their usefulness is still lacking.
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