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
Table 3–1. Genetic Causes of Epilepsy |Favorite Table|Download (.pdf)
Table 3–1. Genetic Causes of Epilepsy
|Lysosomal storage diseases|
|Phakomatoses—tuberous sclerosis, von Hippel–Lindau disease, neurofibromatosis|
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.
Table 3–2. Toxic/Metabolic Causes of Seizures