Seizures

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74 Seizures

A seizure is a transient neurologic event caused by excessive or synchronous cortical neuronal activity in the brain. This can manifest as involuntary changes in body movement or function, sensation, awareness, or behavior. Seizures can be related to temporary conditions or associated with epilepsy, the syndrome of recurrent, unprovoked seizures.

Epilepsy is the most common serious neurologic condition, affecting 50 million people worldwide with prevalence in the United States of about 1%. Incidence rates vary by age with peaks both in early childhood and in adults older than the age of 65 years. Children with epilepsy are at higher risk for learning disorders and behavior problems.

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).

Figure 74-3 Epilepsy syndromes.

Febrile Seizures

Febrile seizures are very common in childhood, affecting one in every 25 children between the ages of 6 months and 6 years. Children with recurrent febrile seizures are not considered to have epilepsy because the seizures are provoked by fever. Simple febrile seizures occur in neurologically normal children, are generalized, last less than 15 minutes, and do not occur more than once in a 24-hour period. Children with simple febrile seizures are at no greater risk for epilepsy than the general population. The risk is greater in children with complex febrile seizures (focal, prolonged, or multiple within 1 day) and in those with abnormal neurologic examination results or if they have a family history of epilepsy.

Epilepsy Syndromes

Certain patterns of epilepsy in childhood have been further classified into syndromes (Figure 74-3). The diagnosis of these syndromes can further guide treatment choices and help to predict developmental outcome. The etiology may be symptomatic (secondary to a known cause), idiopathic (presumed to be genetic), or cryptogenic (presumed to be symptomatic but with an unknown underlying abnormality).

West’s syndrome is the clinical triad of infantile spasms, an interictal EEG pattern termed hypsarrhythmia, and developmental delay or deterioration. Infantile spasms are sudden, brief flexor or extensor myoclonic jerks, which often occur in clusters upon waking or falling asleep. The cause of the syndrome may be symptomatic or cryptogenic. The typical age range is from 2 months to 2 years, but most children present in the first year of life. Although the spasms usually remit by age 2 years, often other seizure types emerge.

Lennox-Gastaut syndrome is a severe form of symptomatic generalized epilepsy. Seizures typically begin between 1 and 7 years of age and there are often premorbid developmental delays. Common seizure types include tonic, atonic, myoclonic, and atypical absence seizures. These patients are often refractory to treatment.

Benign rolandic epilepsy is the most common form of idiopathic focal epilepsy. The seizures usually occur upon awakening and involve unilateral facial sensory or motor symptoms, often with speech arrest, but without impairment of consciousness. The onset is typically between 3 and 14 years of age, and seizures usually resolve by the late teenage years. Treatment is often not necessary unless there is secondary generalization or seizures occur during the day.

Childhood absence epilepsy is a generalized idiopathic epilepsy syndrome affecting neurologically normal children between 4 and 10 years old. Absence seizures may be subtle and are often underrecognized. The EEG shows characteristic 3-Hz spike and wave discharges. The absence seizures occur multiple times a day and may be provoked in the pediatrician’s office with hyperventilation.

Juvenile myoclonic epilepsy begins in the teenage years with myoclonic jerks; tonic-clonic seizures; and occasionally, absence seizures. The myoclonic jerks are typically bilateral and occur within the first few hours of waking. Patients will often describe dropping a toothbrush or silverware during breakfast. The EEG shows spike and wave complexes that may be precipitated by photic stimulation and sleep deprivation. It is an idiopathic generalized epilepsy that usually requires lifelong treatment.