Porth's Essentials of Pathophysiology, 4e

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Disorders of Brain Function

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not the result of a CNS infection or metabolic disor- der. The fact that febrile seizures occur in this age group suggest that factors related to specific stages of brain development contribute to their occurrence. 59 A simple febrile seizure is a primary generalized seizure associ- ated with fever that lasts for a maximum of 15 minutes and does not recur within a 24-hour period. Between 2% and 5% of neurologically healthy infants experience one simple seizure without any long-term ill effects. 59 Complex febrile seizures are more prolonged (>15 min- utes), are focal, and/or recur within 24 hours. Febrile status epilepticus is a febrile seizure lasting longer than 30 minutes. Whether prolonged febrile seizures lead to epilepsy is still uncertain. 59 Children who present with complex febrile seizures or status epilepticus require a detailed history and thorough general and neurological examination. Unprovoked (Epileptic) Seizures The International League Against Epilepsy (ILAE) Com­ mission on Classification and Terminology determines seizure type by clinical symptoms and EEG activity. 60 It divides epileptic seizures into two broad categories: focal and generalized. Focal seizures are those in which the seizure begins in a specific or focal area of one cere- bral hemisphere. Generalized seizures are those which begin simultaneously in both hemispheres. The system also has a category of unknown origin, such as epileptic spasms (Chart 37-1). Focal Seizures Focal seizures, which are the most common type of sei- zures among newly diagnosed cases of epilepsy, can be viewed as those with neural networks limited to one CHART 37-1   Classification of Epileptic Seizures Generalized Seizures Tonic–clonic (in any combination) Absence Typical Atypical Absence with special features Myoclonic

Seizure Disorders A seizure represents an abrupt and transient occurrence of signs and/or symptoms resulting from an abnormal, excessive discharge from an aggregate of neurons in the brain. 7,54–57 Manifestations of a seizure, which vary according to site of discharge, can include sensory, motor, autonomic, or psychic phenomena. A convulsion refers specifically to a motor seizure involving the entire body. Seizure activity is the most common disorder encountered in pediatric neurology, and among adults its incidence is exceeded only by cerebrovascular disorders. 57 In most persons, the first seizure episode occurs before 20 years of age. 58 After 20 years of age, a seizure is caused most often by a structural change, trauma, tumor, or stroke. Clinically, seizures may be categorized as provoked (secondary or acute symptomatic) or unprovoked (pri- mary or idiopathic). 7,55 Provoked seizures may occur during almost all serious illnesses or injuries affecting the brain, including metabolic derangements, infections, tumors, drug abuse, vascular lesions, and brain injury. Unprovoked seizures are those for which no identifi- able cause can be determined, and are thought to be genetic. Most unprovoked seizures occur in the setting of an epileptic syndrome. Persons with this type of sei- zure usually require chronic administration of antiepi- leptic medications to limit seizure recurrences. Epilepsy is characterized by recurrent seizures that are not pro- voked by other illnesses or circumstances. 55–60 Many theories have been proposed to explain the cause of the abnormal brain electrical activity that occurs with seizures. Seizures may be caused by alterations in perme- ability or distribution of ions across neuronal cell mem- branes. Another cause may be decreased inhibition of excitability of neurons. Neurotransmitter imbalances such as an acetylcholine excess or γ -aminobutyric acid (GABA, an inhibitory neurotransmitter) deficiency have also been proposed as causes. Certain epilepsy syndromes have been linked to specific genetic mutations in ion channels. Provoked Seizures Provoked seizures include febrile seizures, seizures pre- cipitated by systemic metabolic conditions, and those that follow a primary insult to the CNS. Transient sys- temic metabolic disturbances may precipitate seizures. Examples include electrolyte imbalances, hypoglycemia, hypoxia, hypocalcemia, uremia, alkalosis, and rapid withdrawal of sedative drugs. Specific CNS injuries such as toxemia of pregnancy, water intoxication, meningi- tis, trauma, cerebral hemorrhage and stroke, and brain tumors may precipitate a seizure. In most cases of pro- voked seizures, treatment of the immediate underlying cause often results in their resolution. Febrile Seizures One form of provoked seizures is febrile seizures that occur in children, between the ages of 6 and 60 months, with a temperature of 100.4°F (38°C) or higher that is

Myoclonic atonic Myoclonic tonic

Clonic Tonic Atonic Focal Seizures Unknown

Epileptic spasms

Adapted from Berg AT, Berkovic SF, Brodie MJ, et al. Revised terminology and concepts for organization of seizures and epilepsy: Report of ILAE Committee on Classification and Terminology, 2005–2009. Epilepsia. 2010;51(4):678.