An epileptic seizure is a change in neurologic function (motor,
sensory, experiential, or autonomic) that is associated with an
abnormal synchronous discharge of cortical neurons. Usually that
discharge can be recorded by routine electroencephalogram (EEG)
using scalp electrodes, although occasionally, because the discharge’s
location is on a surface distant from the scalp (eg, mesial temporal,
orbitofrontal, mesial frontal, basal, or insular cortex), it can
only be recorded by surgically implanted electrodes. Although the
term seizure is sometimes used to refer to any
paroxysmal event, in this chapter seizure always
refers to an epileptic seizure, driven by an abnormal neuronal discharge.
A convulsion is an epileptic seizure that results in involuntary
muscle contractions. The term epileptic seizure always
requires some clinical change in the patient, either observed by
others or reported by the patient himself or herself. Occasionally,
a seizure discharge is recorded on the EEG without any associated
clinical change. Such discharges are referred to as electrographic
seizures or electrographic seizure patterns.
Epilepsy refers to a tendency to spontaneous, recurrent seizures usually
defined by the experience of having had two or more unprovoked seizures.
This definition excludes certain types of provoked seizures, such
as seizures caused by fever during childhood (febrile seizures),
seizures caused by a temporary metabolic derangement such as hypoglycemia
or hyponatremia, or seizures that occur in the setting of an acute
central nervous system (CNS) insult such as stroke, trauma, or meningitis. Seizures
that occur exclusively during the newborn period are also traditionally
excluded from the definition of epilepsy because the majority of
these are considered provoked seizures.
A Note on the Terms
Idiopathic, Cryptogenic, and Symptomatic
The term idiopathic epilepsy literally refers
to an epilepsy “unto itself” (idios, Greek),
meaning an epilepsy that has not occurred as a consequence of another
condition or disorder (eg, head trauma) but a situation in which
epilepsy is the disorder. The primary generalized epilepsies come
under this category, and in this usage, the term primary is synonymous
with idiopathic. The genetic focal epilepsy syndromes
also belong to this category of idiopathic epilepsies. Note that
the term idiopathic epilepsy does not imply an
epilepsy without known cause, as the genetic underpinnings of the
primary generalized (idiopathic) epilepsies are rapidly being elucidated.
The term idiopathic epilepsy does not, however,
simply apply to any epilepsy syndrome in which all neurological
testing is negative. In some instances, an underlying cause is suspected,
although it cannot be specifically identified. Such cases are referred
to as cryptogenic epilepsy (the cause is hidden but
presumed to exist). Finally, the term symptomatic epilepsy is used
for a seizure disorder that has a clear cause (eg, the seizures
that follow the occurrence of a stroke).
Variations in the reported population rates of epilepsy in children
may be due to true differences in the populations studied but ...