ILAE definition of Seizure:
A seizure is (1) transient (2) occurrence of symptoms and signs (3) due to abnormal enhanced synchronous neuronal activity (4) in the brain
From: Fisher, R. S., Boas, W. v. E., Blume, W., Elger, C., Genton, P., Lee, P. and Engel, J. (2005), Epileptic Seizures and Epilepsy: Definitions Proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE). Epilepsia, 46: 470–472.
Discussion:
(1) It has an onset and termination - transient
(2) Clinical manifestations: Seizure presentation depends on location of onset in the brain, patterns of propagation, maturity of the brain, confounding disease processes, sleep–wake cycle, medications, and a variety of other factors. Seizures can affect sensory, motor, and autonomic function; consciousness; emotional state; memory; cognition; or behavior. Not all seizures affect all of these factors, but all influence at least one. In this context, sensory manifestations are taken to include somatosensory, auditory, visual, olfactory, gustatory, and vestibular senses, and also more complex internal sensations consisting of complex perceptual distortions. In previous definitions, these complex internal sensations were referred to as “psychic” manifestations of seizures.
(3) Hughlings Jackson in 1870 provided a now classic definition of an epileptic seizure as a “symptom … an occasional, an excessive and a disorderly discharge of nerve tissue.” By “disorderly,” Jackson probably meant “capable of producing dysfunction,” which is certainly accurate. However, EEG discharges during epileptic seizures are orderly and relatively stereotyped. Firing of neurons may involve inhibition as well as excitation, so it is not always the case that an epileptic seizure involves an excess of excitation over inhibition. A feature more common to epileptic seizures is abnormal enhanced synchrony of neurons.
(4) Definition of an epileptic seizure becomes operationally difficult without ascribing it to the brain. Trigeminal neuralgia, for example, can result from an abnormal enhanced synchrony of neurons in the trigeminal ganglion or the fifth cranial nerve, but would not be considered an epileptic seizure. Neither would hyperactive spinal reflexes resulting in excessive discharge of anterior horns cells and tonic stiffening of a limb. Cerebral cortex is the primary element in the generation of epileptic seizures, but it is not the only one. In some circumstances, epileptic seizures can originate in thalamocortical interactive systems or in the brainstem.
Some further questions to be answered:
1. Why does it have to be 'transient'? Some seizures are fairly prolonged.
Ans: More than transient, what it really implies is that there is a definite onset (change from baseline) and termination (return to baseline activity). That is, there has to be a beginning and an end to this phenomenon.
2. So, is there a situation where we can have abnormal enhanced synchrony that is present from the time of development of brain (no beginning) or persistent abnormal enhanced synchrony (no end)?
Ans:??
3. Why does the abnormal enhanced synchronous activity occur transiently at certain times in certain brains?
Ans: This assumes that there have to be certain provoking factors (time) with neurons that are susceptible (threshold).
4. What are triggering factors versus provoking factors?
Ans: Some seizures are provoked, that is, they occur in the setting of metabolic derangement, drug or alcohol withdrawal, and acute neurologic disorders such as stroke or encephalitis. Such patients are not considered to have epilepsy, because the presumption is that these seizures would not recur in the absence of the provocation. (from Uptodate)
Triggers: Some patients with epilepsy tend to have seizures under particular conditions, and their first seizure may provide a clue to their so-called seizure trigger. Triggers include (but are not limited to) strong emotions, intense exercise, loud music, and flashing lights. Other physiological conditions such as fever, the menstrual period, lack of sleep, and stress can also precipitate seizures, probably by lowering seizure threshold rather than directly causing a seizure. As a result, the temporal relationship to the presenting seizure is often less clear. Triggers may also precipitate nonepileptic paroxysmal disorders, especially syncope.
However, the majority of patients with epilepsy have no identifiable or consistent trigger to their seizures. In addition, triggers are the sole cause of epileptic seizures in only a very small percentage of patients.
4. So, when do we say that someone has epilepsy?
Ans: We can go back to the article cited above. But generally, epilepsy is characterized by recurrent epileptic seizures due to a genetically determined or acquired brain disorder. Approximately 0.5 to 1 percent of the population has epilepsy.
Discussion:
(1) The central concept in the definition of epilepsy is an enduring alteration in the brain that increases the likelihood of future seizures. The diagnosis of epilepsy, under this concept, would not require two seizures; it would require only one epileptic seizure in association with an enduring disturbance of the brain capable of giving rise to other seizures. Multiple epileptic seizures due to multiple different causes in the same patient would not be considered to be epilepsy. A single epileptic seizure due to an enduring epileptogenic abnormality would indicate epilepsy, and a single epileptic seizure in a normal brain would not.
(2) At times, epilepsy must be defined by more than just the recurrence, or a potential for recurrence, of seizures. For some people with epilepsy, behavioral disturbances, such as interictal and postictal cognitive problems, can be part of the epileptic condition. Patients with epilepsy may suffer from stigma, exclusion, restrictions, overprotection, and isolation, which also become part of the epileptic condition. Seizures and the potential for recurrence of seizures also often have psychological consequences for the patient and for the family.
(3) At least one seizure is required to establish the presence of epilepsy; a predisposition, as determined, for example, by a family history, or by the presence of epileptiform EEG changes, is not sufficient to determine epilepsy. The definition does not include a requirement that the seizure be “unprovoked,” a feature of several prior individual definitions. Instead, the definition requires, in addition to at least one seizure, the presence of an enduring alteration in the brain.
Further questions:
1. How do we judge that an individual has "an enduring disturbance of the brain capable of giving rise to further seizures"?
Ans: to be continued....
A seizure is (1) transient (2) occurrence of symptoms and signs (3) due to abnormal enhanced synchronous neuronal activity (4) in the brain
From: Fisher, R. S., Boas, W. v. E., Blume, W., Elger, C., Genton, P., Lee, P. and Engel, J. (2005), Epileptic Seizures and Epilepsy: Definitions Proposed by the International League Against Epilepsy (ILAE) and the International Bureau for Epilepsy (IBE). Epilepsia, 46: 470–472.
Discussion:
(1) It has an onset and termination - transient
(2) Clinical manifestations: Seizure presentation depends on location of onset in the brain, patterns of propagation, maturity of the brain, confounding disease processes, sleep–wake cycle, medications, and a variety of other factors. Seizures can affect sensory, motor, and autonomic function; consciousness; emotional state; memory; cognition; or behavior. Not all seizures affect all of these factors, but all influence at least one. In this context, sensory manifestations are taken to include somatosensory, auditory, visual, olfactory, gustatory, and vestibular senses, and also more complex internal sensations consisting of complex perceptual distortions. In previous definitions, these complex internal sensations were referred to as “psychic” manifestations of seizures.
(3) Hughlings Jackson in 1870 provided a now classic definition of an epileptic seizure as a “symptom … an occasional, an excessive and a disorderly discharge of nerve tissue.” By “disorderly,” Jackson probably meant “capable of producing dysfunction,” which is certainly accurate. However, EEG discharges during epileptic seizures are orderly and relatively stereotyped. Firing of neurons may involve inhibition as well as excitation, so it is not always the case that an epileptic seizure involves an excess of excitation over inhibition. A feature more common to epileptic seizures is abnormal enhanced synchrony of neurons.
(4) Definition of an epileptic seizure becomes operationally difficult without ascribing it to the brain. Trigeminal neuralgia, for example, can result from an abnormal enhanced synchrony of neurons in the trigeminal ganglion or the fifth cranial nerve, but would not be considered an epileptic seizure. Neither would hyperactive spinal reflexes resulting in excessive discharge of anterior horns cells and tonic stiffening of a limb. Cerebral cortex is the primary element in the generation of epileptic seizures, but it is not the only one. In some circumstances, epileptic seizures can originate in thalamocortical interactive systems or in the brainstem.
Some further questions to be answered:
1. Why does it have to be 'transient'? Some seizures are fairly prolonged.
Ans: More than transient, what it really implies is that there is a definite onset (change from baseline) and termination (return to baseline activity). That is, there has to be a beginning and an end to this phenomenon.
2. So, is there a situation where we can have abnormal enhanced synchrony that is present from the time of development of brain (no beginning) or persistent abnormal enhanced synchrony (no end)?
Ans:??
3. Why does the abnormal enhanced synchronous activity occur transiently at certain times in certain brains?
Ans: This assumes that there have to be certain provoking factors (time) with neurons that are susceptible (threshold).
4. What are triggering factors versus provoking factors?
Ans: Some seizures are provoked, that is, they occur in the setting of metabolic derangement, drug or alcohol withdrawal, and acute neurologic disorders such as stroke or encephalitis. Such patients are not considered to have epilepsy, because the presumption is that these seizures would not recur in the absence of the provocation. (from Uptodate)
Triggers: Some patients with epilepsy tend to have seizures under particular conditions, and their first seizure may provide a clue to their so-called seizure trigger. Triggers include (but are not limited to) strong emotions, intense exercise, loud music, and flashing lights. Other physiological conditions such as fever, the menstrual period, lack of sleep, and stress can also precipitate seizures, probably by lowering seizure threshold rather than directly causing a seizure. As a result, the temporal relationship to the presenting seizure is often less clear. Triggers may also precipitate nonepileptic paroxysmal disorders, especially syncope.
However, the majority of patients with epilepsy have no identifiable or consistent trigger to their seizures. In addition, triggers are the sole cause of epileptic seizures in only a very small percentage of patients.
4. So, when do we say that someone has epilepsy?
Ans: We can go back to the article cited above. But generally, epilepsy is characterized by recurrent epileptic seizures due to a genetically determined or acquired brain disorder. Approximately 0.5 to 1 percent of the population has epilepsy.
ILAE definition of Epilepsy:
Epilepsy is (1) a disorder of the brain characterized by an enduring
predisposition to generate epileptic seizures (2) and by the neurobiologic,
cognitive, psychological, and social consequences of this condition. (3) The
definition of epilepsy requires the occurrence of at least one
epileptic seizure.Discussion:
(1) The central concept in the definition of epilepsy is an enduring alteration in the brain that increases the likelihood of future seizures. The diagnosis of epilepsy, under this concept, would not require two seizures; it would require only one epileptic seizure in association with an enduring disturbance of the brain capable of giving rise to other seizures. Multiple epileptic seizures due to multiple different causes in the same patient would not be considered to be epilepsy. A single epileptic seizure due to an enduring epileptogenic abnormality would indicate epilepsy, and a single epileptic seizure in a normal brain would not.
(2) At times, epilepsy must be defined by more than just the recurrence, or a potential for recurrence, of seizures. For some people with epilepsy, behavioral disturbances, such as interictal and postictal cognitive problems, can be part of the epileptic condition. Patients with epilepsy may suffer from stigma, exclusion, restrictions, overprotection, and isolation, which also become part of the epileptic condition. Seizures and the potential for recurrence of seizures also often have psychological consequences for the patient and for the family.
(3) At least one seizure is required to establish the presence of epilepsy; a predisposition, as determined, for example, by a family history, or by the presence of epileptiform EEG changes, is not sufficient to determine epilepsy. The definition does not include a requirement that the seizure be “unprovoked,” a feature of several prior individual definitions. Instead, the definition requires, in addition to at least one seizure, the presence of an enduring alteration in the brain.
Further questions:
1. How do we judge that an individual has "an enduring disturbance of the brain capable of giving rise to further seizures"?
Ans: to be continued....
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