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Absence seizure
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Absence seizures are one of several kinds of seizures. These seizures are sometimes referred to as petit mal seizures (from the French for "little illness", a term dating from the late 1700s).
In absence seizures, the person may appear to be staring into space with or without jerking or twitching movements of the eye muscles. These periods last for seconds, or even tens of seconds.
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Encyclopedia
Absence seizures are one of several kinds of seizures. These seizures are sometimes referred to as petit mal seizures (from the French for "little illness", a term dating from the late 1700s).
In absence seizures, the person may appear to be staring into space with or without jerking or twitching movements of the eye muscles. These periods last for seconds, or even tens of seconds. Those experiencing absence seizures sometimes move from one location to another without any purpose. Under normal circumstances thalamocortical oscillations maintain normal consciousness of an individual, however in certain circumstances the normal pattern can become disrupted; thereby leading to an episode of absence. Drugs, such as ethosuximide work by binding to t-type Ca2+ channels on thalamic neurones to modify these oscillations and prevent these episodes from occurring.
Types
Absence seizures may occur in several forms of epilepsy. Absence epilepsy refers to epilepsy in which the only seizures are absence seizures. Absence epilepsy is often characterized by age of onset, e.g., childhood absence epilepsy for epilepsy beginning in childhood between the ages of 4 and 12. Absence epilepsy has also been termed pyknolepsy (from the Greek "pyknos", meaning closely packed, dense, or aggregated) and was commonly used in early 20th century German psychiatry
Epilepsy is the most common cause of recurrent seizures, where seizures are single events that reoccur with seemingly random frequency. Single seizures can be caused by blows to the head, fever (febrile seizure), reactions to medications, tumours, or as a symptom of a larger disease, among other causes.
Just as there are many different kinds of seizures, there are many different kinds of epilepsy. Doctors have identified hundreds of different epilepsy syndromes - disorders characterized by a specific set of symptoms that include epilepsy. Some of these syndromes appear to be hereditary. For other syndromes, the cause is unknown. Epilepsy syndromes are frequently described by their symptoms or by where in the brain they originate. People should discuss the implications of their type of epilepsy with their doctors to understand the full range of symptoms, the possible treatments, and the prognosis.
Presentation
Some people with absence epilepsy report seeing flashing or blinking lights in the corner of one or both eyes, possibly followed by a 'flash vision change', shortly before they slip into a seizure . Some have purposeless movements during their seizures, such as a jerking arm or rapidly blinking eyes. Others have no outwardly noticeable symptoms except for brief times when they are "spaced out", as repeated absence seizures can cause momentary lapses of consciousness. Immediately after a seizure, the person will usually resume whatever he or she was doing prior to its onset.
These seizures can happen a few times a day or in some cases hundreds of times a day, to the point that the person cannot concentrate in school or other situations requiring sustained, concentrated attention. Childhood absence epilepsy may stop when the child reaches puberty. Absence seizures usually have no lasting effect on intelligence or other brain function.
It is well known that bright lights, nervous, stressful, uncomfortable situations, or other strong sensory stimuli may trigger seizures. Hyperventilation is also a common trigger. However, loud noises can help to either bring a person back to consciousness or keep him or her conscious. Reciting one's name can be very helpful in an emergency as can repetitively asking the victim to "stay with you". Such can be accomplished by counting methods, alphabets and so on.
A person having an absence seizure shows no emotional expressions during the absent period. While the ability to express emotion in the face may be dissociated from the experience of emotion, the lack of any emotionally charged facial expression may indicate that a certain level of consciousness and arousal are needed to experience emotions.
A bilateral synchronous, symmetrical 3-Hz spike-and-wave discharge EEG pattern accompanies absence seizures.
Treatment
The primary goal of treatment of recurrent absence seizures is to prevent accidental injury that may occur through the lapses of consciousness that accompany seizures. For those with frequent seizures, treatment also seeks to prevent them from interfering with learning or other activities of daily life.
The purpose of medication of absence seizures is to accomplish the goals above, by eliminating or reducing the frequency of the absence seizures, without causing side-effects more serious than the epilepsy itself.
Certain anticonvulsant drugs are used to minimize the number of seizure episodes. Absence seizures appear to respond well to sodium valproate, ethosuximide, and lamotrigine. Each of these medications has potential side effects, some of them possibly serious, which makes it important that the patient and/or their caregivers understand the specific medication prescribed.
Clonazepam (Klonopin, Rivotril) is effective in the short term but is not generally recommended for treatment of absence seizure due to the rapid development of tolerance and high frequency of side effects.
In the treatment of absence seizures there is often insufficient evidence for which of the available medications has the best combination of safety and efficacy for a particular patient. Nor is it easily known how long a medication must be continued before an off-medication trial should be conducted to determine whether the individual has outgrown the absence seizures, as is often the case in children.
To date there have been no published results of any large, double-blind, placebo-controlled studies comparing the efficacy and safety of these or any other medications for absence seizures. The studies that exist have been small and not produced clear conclusions.
The U.S. government is currently sponsoring such a study. Its purpose is to determine the best initial treatment for childhood absence epilepsy from among valproic acid, ethosuximide and lamotrigine. In addition the researchers hope to develop future methods to help in choosing the best medicine for a child diagnosed with absence seizures. The 5-year study began in 2004 and is expected to involve more than 400 children.
Also included in the study will be pharmacokinetics and pharmacogenetics research. Pharmacokinetics is the study of how the body absorbs, distributes, metabolizes, and excretes drugs. Pharmacogenetics is the study of genetic determinants of the responses to drugs. Knowledge gained from this study may improve the individualized treatment of children with absence seizures.
See also
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