A general simplified definition of a seizure is a sudden temporary change in brain function caused by an abnormal rhythmic electrical discharge. Epilepsy is, simply put, a state of recurrent seizure activity. The mechanism whereby a seizure turns into epilepsy, a process known as epileptogenesis, is controversial.

Seizures are common in humans, with an incidence of approximately 80/100,000 per year and an overall risk of epilepsy of 1% to 3%.1 Status epilepticus is a less common form of severe prolonged seizure activity with a high morbidity and mortality.

Seizures arise secondary to a number of etiologies. Idiopathic seizures, or “cryptogenic” seizures, are fairly common. Contrary to what many patients and families might think, the inability to find a cause for the seizure is not necessary “bad.” In fact, this may portend a somewhat better prognosis for long-term seizure control. Febrile seizures are common in children and are covered in detail in Chapter 4.

Trauma contributes to the risk of seizures in two fairly distinct fashions. Early posttraumatic seizures are typically associated with intracranial hemorrhage, focal neurological deficits, posttraumatic amnesia exceeding 24 hours, and linear skull fractures. Late posttraumatic seizures are also associated with intracranial hemorrhage and posttraumatic amnesia exceeding 24 hours, but are usually seen in patients with depressed skull fractures and with the injury after age 16 years.2-4

A number of congenital malformations increase the risk for epilepsy. Disorders associated with migrational disorders and structural anomalies often increase the risk of subsequent seizures. The genetic diseases listed in Table 3-1 also increase the risk of epilepsy whether or not they are associated with structural malformations.5-7

Infections are also common causes of seizure activity in the pediatric population. Meningitis and encephalitis can result in seizures either related to the fever or to the direct effects of the infection. These are covered in detail in the chapters on infectious disease. Bacterial infections can result in meningitis, encephalitis, and abscess formation. Herpes simplex virus (HSV) is a well known cause of seizures and can be catastrophic.8 Other viral infections including cytomegalovirus (CMV) infection and various viral encephalitides can result in seizures. Fungal infections and toxoplasmosis also raise the risk of developing seizures.

A wide array of toxic and metabolic disorders can result in seizures. These derangements can cause seizures to occur de novo but can also worsen a pre-existing epilepsy. The common metabolic and toxic causes of seizures are listed in Table 3-2.

Cerebral ischemia is a common cause of seizures in the neonate and in the older adult but is relatively uncommon in the older pediatric population.

Seizures usually occur in the more slowly growing tumors. Tumors located in the supratentorial region cause seizures more frequently than do cerebellar or brainstem tumors.

Epilepsy is divided into several categories with significant differences in the characteristics of the electrical discharges as well as the clinical manifestations. Localization-related epilepsy or partial epilepsy has a primary focus from which the electrical discharges arise. Complex partial seizures occur with alteration of awareness while simple partial seizures have no alteration of awareness. Jacksonian motor seizures, Rolandic epilepsy, temporal lobe epilepsy, and frontal lobe epilepsy are all examples of partial epilepsy.

The Revised International Classification of Epilepsies, Epileptic Syndromes and Related Seizure Disorders divides the localization-related epilepsies as follows:10

• Idiopathic localization-related epilepsy
  
• Symptomatic or secondary localization-related epilepsy
  
• Cryptogenic localization-related epilepsy

Generalized seizures are the other major seizure type. In this category of epilepsy, the seizure affects the entire cortex electrically. Several subtypes of generalized seizures have also been identified, including absence epilepsy with 3-Hz spike and wave activity, generalized tonic-clonic seizures, juvenile myoclonic epilepsy, and progressive myoclonic epilepsy.

The Revised International Classification of Epilepsies, Epileptic Syndromes and Related Seizure Disorders divides the generalized epilepsies as follows10:

• Primary generalized epilepsy
  
• Symptomatic generalized epilepsy
  
• Cryptogenic epilepsy

A number of seizures and epilepsies may be very difficult to categorize. The Revised International Classification of Epilepsies, Epileptic Syndromes and Related Seizure Disorders groups these disorders in the “undetermined” category. These seizures may be divided as follows10:

• Both focal and generalized
  
• Situation-related epilepsy
  
• Febrile convulsions
  
• Isolated seizure
  
• Isolated status epilepticus
  
• Toxic/metabolic

In each of these cases, the electroencephalographic (EEG) findings may be different. The EEG serves as a vitally important tool in the correct diagnosis of the various epilepsy subtypes and syndromes.

Seizure Types

Generalized Tonic-Clonic Seizures

Generalized tonic-clonic seizures typically have no preceding aura but may have a prodrome of apathy or irritability. During the tonic phase, the jaw snaps shut followed by 10 to 15 seconds or longer of tonic spasms, apnea, and cyanosis. The clonic phase usually consists of 1 to 2 minutes of rhythmic generalized muscle contractions and increased blood pressure. The postictal phase lasts for minutes to hours, with confusion, somnolence, and possibly agitation.

The ictal EEG usually consists of generalized spike and wave or polyspike activity. The interictal EEG is highly variable with a normal background in some patients and slowing present in others.

Generalized seizures are rare in newborns. Generalized seizures occur most frequently in children secondary to fevers and metabolic derangements.

Absence Seizures

Absence seizures typically have no preceding aura or prodrome. An absence seizure usually lasts for only several seconds to minutes. There is a sudden interruption of consciousness, staring, 3-Hz blinking, and less frequently automatisms. There is no postictal confusion.11

The ictal EEG usually consists of 3-Hz generalized spike and wave activity with some slowing of the discharge frequency during the seizure. The interictal EEG usually has a normal background. Atypical absence seizures have generalized spike and wave activity but usually have a frequency less than 3 Hz.12

Absence seizures typically start between ages 4 and 10 years and resolve by age 20 years. Atypical absence epilepsy usually occurs in children who are neurologically or developmentally abnormal.13

Febrile Seizures

Febrile seizures occur with a prodromal fever. A simple febrile seizure occurs as a brief generalized tonic clonic seizure occurring after the onset of fever. A complicated febrile seizure has prolonged seizure activity or focal seizure activity. Febrile seizures are covered in detail in Chapter 4.

Juvenile Myoclonic Epilepsy

The seizures associated with juvenile myoclonic epilepsy typically have no preceding aura but may have a prodrome of morning myoclonus. The seizures may consist of generalized tonic-clonic activity; however, absence seizures may also occur. The postictal phase is variable depending on the seizure type.11

The ictal EEG usually consists of generalized polyspike and slow wave activity. The interictal EEG is typically unremarkable.12

The age of onset of juvenile myoclonic epilepsy is typically 10 to 20 years. Patients are usually developmentally and neurologically normal.13

Progressive Myoclonic Epilepsy

The family of disorders known as the progressive myoclonic epilepsies (Table 3-3) consists of a number of loosely related disorders. These epilepsy subtypes are quite rare and have complex presentations and diagnostic findings. Most of these disorders have a genetic basis, though sporadic cases have occurred in some cases (Table 3-4). The EEG associated with these disorders is variable. The background is often slow. The seizures are typically generalized.11

Infantile Spasms

West syndrome typically begins between 3 months and 3 years of age.14-16 The seizures associated with West syndrome consist of a jack-knifing movement and myoclonus. The EEG consists of a hypsarrhythmia pattern with bursts of asynchronous slow waves; spikes and sharp waves alternate with a suppressed EEG.17 The clinical features of West syndrome include infantile spasms and mental retardation, which varies according to the etiology of the spasms.

Aicardi syndrome is an X-linked disorder present from birth that is associated with infantile spasms. The seizures are described as infantile spasms, but alternating hemiconvulsions may also be seen. The clinical features of Aicardi syndrome include coloboma, chorioretinal lacunae, agenesis of the corpus callosum, vertebral anomalies, and seizures.18

Lennox–Gastaut Syndrome

Lennox–Gastaut syndrome typically begins between 1 and 10 years of age. There are multiple seizure types, associated with variable degrees of mental retardation.

The EEG reveals a slow spike wave complex with a frequency of 1 to 2.5 Hz, multifocal spikes, and generalized paroxysmal fast activity (GPFA).19

Partial Seizures: Localization-Related Epilepsy

Jacksonian motor seizures are simple partial seizures with no alteration of consciousness. These seizures begin with tonic contractions of the face, fingers, or feet and transform into clonic movements that march to other muscle groups on the ipsilateral hemibody. There is no alteration in consciousness, but postictal aphasia may occur if the primary epileptogenic zone involves the dominant hemisphere. Simple partial seizures may involve autonomic (Table 3-5), sensory, motor, or psychic functions.

Complex Partial Seizures

Benign Rolandic Epilepsy

Benign Rolandic epilepsy usually begins between ages 5 and 10 years and is transmitted in an autosomal dominant pattern with variable penetrance. It is fairly common, with an incidence of 21/100,000 children.20 The clinical features include a single nocturnal seizure with clonic movement of the mouth and gurgling. Secondary generalization is common. Alteration in consciousness, aura, and postictal confusion are rare. The seizures resolve by age 16 years.21,22

The interictal EEG consists of central and mid-temporal high-amplitude spike and wave with a characteristic dipole. The ictal EEG usually consists of a focal central or mid-temporal ictal onset, with the possibility of secondary generalization.23,24