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INTRODUCTION AND PATHOPHYSIOLOGY
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A seizure is an episode of abnormal neurologic function caused by inappropriate electrical discharge of brain neurons. Neuronal electrical discharge, in its most simple form, can be thought of as the homeostasis of glutaminergic (excitatory) and γ-aminobutyric acid (inhibitory) activity. The seizure is the clinical attack experienced by the patient in the setting of inappropriate excitatory activity. Some patients with "epileptic" electroencephalographic (EEG) discharges may not experience any overt clinical symptoms. Some seizure-like episodes may be due to causes other than abnormal brain electrical activity, but such attacks are not true seizures.
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Epilepsy is a clinical condition in which an individual is subject to recurrent seizures. It implies a fixed, more excitatory condition of the brain with a lower seizure threshold. The term epileptic does not refer to an individual with recurrent seizures caused by reversible conditions such as alcohol withdrawal, toxins, hypoglycemia, or other metabolic derangements.
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Primary, or idiopathic, seizures are those in which no evident cause can be identified. Secondary, or symptomatic, seizures are a consequence of an identifiable neurologic condition, such as a mass lesion, previous head injury, or stroke. Electrical stimulation of the brain, convulsant potentiating drugs, profound metabolic disturbances, or a sharp blow to the head all may cause reactive seizures in otherwise normal individuals. Reactive seizures are generally self-limited, and a reactive seizure is not considered to be a seizure disorder or epilepsy.
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There are further definitions of seizures based on clinical factors: a provoked seizure has an acute precipitating event within 7 days of the insult; an unprovoked seizure has no acute precipitating factor or may result from a very remote incident; status epilepticus is seizure activity for ≥5 minutes or two or more seizures without regaining consciousness between seizures1; and refractory status epilepticus is persistent seizure activity despite the IV administration of adequate amounts of two antiepileptic agents.
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SEIZURE CLASSIFICATION
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The International League Against Epilepsy recommends dividing seizures into two major groups: generalized seizures and partial seizures (Table 171–1). When there are inadequate data to categorize the seizure, the seizure is considered unclassified.
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Generalized seizures are thought to be caused by a nearly simultaneous activation of the entire cerebral cortex, perhaps caused by an electrical discharge originating deep in the brain and spreading outward. The attacks begin with abrupt loss of consciousness. Loss of consciousness may be the only clinical manifestation of ...