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A seizure is an episode of abnormal neurologic function caused by the inappropriate electrical discharge of brain neurons. Primary seizures are those without an identified specific cause. Secondary seizures result from another identifiable neurologic condition, such as a mass, head injury, or stroke (Table 145-1).
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Seizures are classified as generalized or partial. Generalized seizures are characterized by widespread involvement of the entire cerebral cortex and are typically associated with an abrupt loss of consciousness. Generalized tonic-clonic seizures (grand mal) often begin with a sudden onset of muscle rigidity where the trunk and extremities are extended and the patient falls to the ground. This rigid (tonic) phase is followed by a symmetric and rhythmic (clonic) jerking of the trunk and extremities. Generalized seizures are commonly associated with incontinence and an immediate postictal period where the patient remains flaccid and unconscious. A typical episode may last from 60 to 90 seconds with a gradual return of consciousness afterwards, although postictal confusion may persist for hours. Absence (petit mal) seizures are a subclass of generalized seizures typically seen in school-aged children and often last only a few seconds. Patients suddenly lose consciousness without losing postural tone and appear confused, detached, or withdrawn. An absence seizure typically ends abruptly with a return to normal functioning.
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Partial seizures are due to electrical discharges that begin in a localized region of the cerebral cortex. These seizures may remain localized to one area of the brain or may later spread to other regions. Partial seizures are described as simple, in which consciousness is not affected, or complex, in which consciousness is altered. Complex partial seizures are often due to discharges in the temporal lobe (also termed temporal lobe seizures) and may include automatisms, visceral complaints, hallucinations, memory disturbances, distorted perception, and affective disorders.
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Status epilepticus is defined as a single seizure lasting for longer than 5 minutes, or as two or more seizures that occur sequentially without an intervening recovery of consciousness. Nonconvulsive status epilepticus is characterized by altered mental status without perceptible muscular convulsive activity and is confirmed by electroencephalogram (EEG).
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