C h a p t e r 3 7
Disorders of Brain Function
945
Seizure Disorders
A
seizure
represents an abrupt and transient occurrence
of signs and/or symptoms resulting from an abnormal,
excessive discharge from an aggregate of neurons in
the brain.
7,54–57
Manifestations of a seizure, which vary
according to site of discharge, can include sensory, motor,
autonomic, or psychic phenomena. A
convulsion
refers
specifically to a motor seizure involving the entire body.
Seizure activity is the most common disorder encountered
in pediatric neurology, and among adults its incidence is
exceeded only by cerebrovascular disorders.
57
In most
persons, the first seizure episode occurs before 20 years
of age.
58
After 20 years of age, a seizure is caused most
often by a structural change, trauma, tumor, or stroke.
Clinically, seizures may be categorized as provoked
(secondary or acute symptomatic) or unprovoked (pri-
mary or idiopathic).
7,55
Provoked seizures
may occur
during almost all serious illnesses or injuries affecting
the brain, including metabolic derangements, infections,
tumors, drug abuse, vascular lesions, and brain injury.
Unprovoked seizures
are those for which no identifi-
able cause can be determined, and are thought to be
genetic. Most unprovoked seizures occur in the setting
of an epileptic syndrome. Persons with this type of sei-
zure usually require chronic administration of antiepi-
leptic medications to limit seizure recurrences.
Epilepsy
is characterized by recurrent seizures that are not pro-
voked by other illnesses or circumstances.
55–60
Many theories have been proposed to explain the cause
of the abnormal brain electrical activity that occurs with
seizures. Seizures may be caused by alterations in perme-
ability or distribution of ions across neuronal cell mem-
branes. Another cause may be decreased inhibition of
excitability of neurons. Neurotransmitter imbalances such
as an acetylcholine excess or
γ
-aminobutyric acid (GABA,
an inhibitory neurotransmitter) deficiency have also been
proposed as causes. Certain epilepsy syndromes have been
linked to specific genetic mutations in ion channels.
Provoked Seizures
Provoked seizures include febrile seizures, seizures pre-
cipitated by systemic metabolic conditions, and those
that follow a primary insult to the CNS. Transient sys-
temic metabolic disturbances may precipitate seizures.
Examples include electrolyte imbalances, hypoglycemia,
hypoxia, hypocalcemia, uremia, alkalosis, and rapid
withdrawal of sedative drugs. Specific CNS injuries such
as toxemia of pregnancy, water intoxication, meningi-
tis, trauma, cerebral hemorrhage and stroke, and brain
tumors may precipitate a seizure. In most cases of pro-
voked seizures, treatment of the immediate underlying
cause often results in their resolution.
Febrile Seizures
One form of provoked seizures is febrile seizures that
occur in children, between the ages of 6 and 60 months,
with a temperature of 100.4°F (38°C) or higher that is
not the result of a CNS infection or metabolic disor-
der. The fact that febrile seizures occur in this age group
suggest that factors related to specific stages of brain
development contribute to their occurrence.
59
A simple
febrile seizure is a primary generalized seizure associ-
ated with fever that lasts for a maximum of 15 minutes
and does not recur within a 24-hour period. Between
2% and 5% of neurologically healthy infants experience
one simple seizure without any long-term ill effects.
59
Complex febrile seizures are more prolonged (>15 min-
utes), are focal, and/or recur within 24 hours. Febrile
status epilepticus is a febrile seizure lasting longer than
30 minutes. Whether prolonged febrile seizures lead to
epilepsy is still uncertain.
59
Children who present with
complex febrile seizures or status epilepticus require a
detailed history and thorough general and neurological
examination.
Unprovoked (Epileptic) Seizures
The International League Against Epilepsy (ILAE) Com
mission on Classification and Terminology determines
seizure type by clinical symptoms and EEG activity.
60
It divides epileptic seizures into two broad categories:
focal and generalized.
Focal seizures
are those in which
the seizure begins in a specific or focal area of one cere-
bral hemisphere.
Generalized seizures
are those which
begin simultaneously in both hemispheres. The system
also has a category of unknown origin, such as epileptic
spasms (Chart 37-1).
Focal Seizures
Focal seizures, which are the most common type of sei-
zures among newly diagnosed cases of epilepsy, can be
viewed as those with neural networks limited to one
CHART 37-1
Classification of Epileptic Seizures
Generalized Seizures
Tonic–clonic (in any combination)
Absence
Typical
Atypical
Absence with special features
Myoclonic
Myoclonic atonic
Myoclonic tonic
Clonic
Tonic
Atonic
Focal Seizures
Unknown
Epileptic spasms
Adapted from Berg AT, Berkovic SF, Brodie MJ, et al. Revised
terminology and concepts for organization of seizures and
epilepsy: Report of ILAE Committee on Classification and
Terminology, 2005–2009. Epilepsia. 2010;51(4):678.
