Etiology and Pathogenesis

Seizures can arise from many different sources (Figure 74-1). Primary seizures are thought to have a genetic or biochemical origin. Intracranial pathology, including tumor, vascular infarct or hemorrhage, arteriovenous malformation, trauma, infection, or congenital or developmental brain defects, can also result in seizure. They may also be provoked by electrolyte abnormalities (hypoglycemia, hypo or hypernatremia, hypocalcemia, hypomagnesemia), infection, anoxia, certain medications, drug intoxication or withdrawal, kidney or liver failure, and inborn errors of metabolism.

Figure 74-1 Causes of seizures.

Clinical Presentation

Seizure Classification

Classifying seizures is the most important first step toward appropriate diagnosis and treatment. Seizures are typically categorized as either partial or generalized. Whereas partial seizures begin in a focal area of the cerebral cortex, generalized seizures are characterized by onset simultaneously in both hemispheres and are usually associated with a loss of consciousness.

Partial seizures are further classified as either simple or complex. In simple partial seizures, consciousness is preserved, but in complex partial seizures, consciousness is impaired. Both types of partial seizures can spread to other cortical areas, resulting in a secondarily generalized seizure.

Symptoms of simple partial seizures are often determined by the cortical area involved. These symptoms may be motor, sensory, autonomic, or psychic in nature. For example, those arising from the motor cortex result in rhythmic movements of the contralateral face, arm, or leg. See Figure 74-2 for more examples.

Figure 74-2 Partial seizures.

A complex partial seizure typically begins with behavioral arrest and is followed by staring, automatisms, and postictal confusion. Occasionally, there is a preceding simple partial seizure or aura, warning of the oncoming seizure. Automatisms can include chewing, lip smacking, mumbling, or picking at clothes. Complex partial seizures typically last less than 3 minutes, and patients have no memory of the event. The postictal state can last from minutes to hours with symptoms of sleepiness, confusion, and headache, and a postictal (“Todd”) hemiparesis, which typically lasts less than 1 day.

Generalized seizures are classified into six major categories: primary generalized tonic-clonic, tonic, clonic, myoclonic, atonic, and absence. The most commonly recognized type is the generalized tonic clonic seizure. These seizures are usually preceded by a cry followed by the sudden onset of tonic stiffening and convulsive movements. They are often associated with biting of the sides of the tongue and urinary incontinence.

Tonic seizures cause sudden stiffening of extensor muscles and are often associated with falls. Clonic seizures are characterized by rhythmic or semirhythmic muscle contractions, typically involving the upper extremities or the face. Myoclonic seizures consist of sudden, brief muscle contractions and may occur in clusters. Atonic seizures typically occur in patients with significant neurologic abnormalities. They are often referred to as drop attacks and result in sudden loss of muscle tone and collapse, frequently resulting in injury.

Absence seizures are brief episodes of impaired consciousness with no aura or postictal confusion. They typically last less than 20 seconds and are accompanied by few or no automatisms. Hyperventilation or photic stimulation often precipitates these seizures, which typically begin during childhood or adolescence, although they may persist into adulthood. In children, these seizures may initially go unnoticed and are often associated with decreased school performance or poor attention. The classic ictal electroencephalographic (EEG) correlate of absence seizures consists of 3-Hz generalized spike and slow-wave complexes (Figure 74-3).

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