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.
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....
