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A seizure is caused by the abnormal synchronous firing of large ensembles of neurons. Epilepsy refers to any neurologic disorder that is characterized by recurrent seizures.
Seizures can be classified as focal, which indicates that the initial abnormal firing is limited to a specific area in one hemisphere, or generalized, which indicates that a large population of neurons in both hemispheres is involved.
Seizures occur because of a change in the brain’s delicate balance of excitatory and inhibitory synaptic processes. This change can be caused by any number of different brain insults, including tumors, strokes, and head injury as well as developmental abnormalities.
Many forms of epilepsy have a genetic component, although the inheritance of epilepsy is rarely simple.
Most anticonvulsants work by modifying the function of sodium or calcium channels or by enhancing GABA-mediated inhibitory synaptic transmission.
Other known actions of a smaller number of anticonvulsants include potentiation of potassium channels, inhibition of glutamatergic transmission, and poorly defined actions on a synaptic vesicle-associated protein termed synaptic vesicle protein 2A (SV2A).
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This chapter is devoted to seizure-related disorders such as epilepsy. Seizures are characterized by uncontrolled firing of sets of neurons in the brain and can have devastating consequences. Seizure disorders are common: approximately 5% to 10% of people will experience at least one seizure in their lifetime. Fortunately, the treatment of seizures has steadily improved with the introduction of safer and more effective anticonvulsant agents.
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SEIZURES AND EPILEPSY
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A seizure is a paroxysmal derangement of cerebral function caused by excessive and generally synchronized activity of a group of neurons. Seizure activity can occur in many different regions of the brain, and its physical manifestations vary according to the region in which it occurs. Thus, the term seizure may refer to a 3-second lapse of consciousness that is barely noticeable to the affected individual or to witnesses of the event. The same term also applies to a “grand mal” tonic–clonic seizure that causes an individual to lose consciousness and contract all muscles of the body followed by a jerking of his or her entire body that is violent enough to result in muscle damage and electrolyte abnormalities.
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In many cases a seizure can be traced to a specific insult, such as head trauma, high fever, or alcohol withdrawal. An isolated seizure does not mean that an individual has epilepsy, a disorder defined by an increased propensity for recurring seizures. The traditional clinical definition of epilepsy is the occurrence of two or more unprovoked seizures. In the US population, epilepsy has a prevalence of 1 in 100 and an incidence of 1 in 2000. Inherited vulnerabilities, focal brain injury, or chronic illness can produce lower seizure thresholds in epileptic individuals, who generally require medication to control their seizures.
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Because there are many varieties of seizures, ...