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Content Update October 2023

Updates are provided in Tables 171-2 and 171-3 to provide additional information on seizure risk factors and treatment of Status Epilepticus. Figure 171-1 has been replaced by Table 171-3. Also see Differential Diagnosis: Cardiac electrical instability or chanellopathies.

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 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.

Epilepsy is a clinical condition in which an individual is subject to recurrent seizures. It implies a fixed, 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 or metabolic derangements.

Primary or idiopathic seizures are those in which no evident cause can be identified. Secondary 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 significant head trauma all may cause reactive seizures in otherwise normal individuals. Reactive seizures are generally self-limited and not considered to be a seizure disorder or epilepsy.

Additional definitions of seizures are based on clinical factors or duration: status epilepticus is seizure activity ≥5 minutes, or two or more seizures without regaining consciousness or returning to one's neurologic baseline between seizures1; refractory status epilepticus is persistent seizure activity despite the IV administration of adequate amounts of two antiepileptic agents.


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.

TABLE 171-1 Classification of Seizures


Generalized seizures are thought to be caused by near 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, and this may be the only clinical manifestation of ...

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