Febrile seizures are defined as events in infancy or childhood that usually occur between three months and five years of age and are associated with a fever, but without evidence of intracranial infection or a defined cause for the seizure.

• Simple febrile seizures are generalized in onset, last less than 15 minutes, and do not occur more than once in 24 hours. Complex seizures last longer, have focal symptoms, and can recur within 24 hours. This review only deals with simple febrile seizures.

• Approximately 2 to 5 percent of children in the United States and Western Europe, and 6 to 9 percent of infants and children in Japan, will have experienced at least one febrile seizure by five years of age.

• Simple febrile seizures may slightly increase the risk of developing epilepsy, but have no known adverse effects on behavior, scholastic performance, or neurocognition.

  We do not know whether antipyretics are useful in treating episodes of fever to prevent seizure recurrence in children with one or more previous simple febrile seizures.

• Intermittent anticonvulsants used in treating episodes of fever to prevent seizure recurrence in children are associated with adverse effects, including hyperactivity; irritability; and difficulties with speech, activity level, or sleep.

  Continuous anticonvulsant treatment may be effective for reducing recurrence in children with a history of simple febrile seizures, but it is associated with adverse effects. For example, phenobarbital is associated with cognitive impairments and behavioral adverse effects (e.g., hyperactivity, irritability, aggressiveness).

• Anticonvulsants do not appear to reduce the risk of epilepsy up to 12 years later in children with a history of simple febrile seizures.

Definition

Febrile seizures are divided into three types: simple febrile seizures, complex febrile seizures, and febrile status epilepticus. The National Institutes of Health define a febrile seizure as “an event in infancy or childhood usually occurring between three months and five years of age associated with a fever, but without evidence of intracranial infection or defined cause for the seizure,” after having excluded children with previous afebrile seizures. Another definition, from the International League Against Epilepsy, is “a seizure occurring in childhood after one month of age associated with a febrile illness not caused by an infection of the central nervous system, without previous neonatal seizures or a previous unprovoked seizure, and not meeting the criteria for other acute symptomatic seizures.”

In working practice, the lower age limit for febrile seizures is generally considered to be six months, given concerns regarding the possibility of an underlying serious, but treatable, infection in younger infants masquerading as a febrile seizure (e.g., meningitis). A simple febrile seizure is a generalized seizure, often tonic-clonic, lasting less than 15 minutes in duration that does not occur more than once in 24 hours, and is followed by full recovery within one hour.

Treatment for the actual seizure is generally not indicated, given the short duration. In over 80 percent of children, the duration of the febrile seizure is less than 10 minutes, and in only about 9 percent of children do they last longer than 15 minutes. Often, by the time the child presents to a hospital, the seizure has already stopped. A febrile seizure may also be the presenting sign of a fever episode.

This review does not include children experiencing complex febrile seizures, which are characterized by any of the following features: longer than 15 minutes in duration, focal symptoms, recurrence within 24 hours, and not followed by full consciousness within one hour. Investigations, including neuroimaging and lumbar puncture, are often warranted. Also excluded from this review are children experiencing febrile status epilepticus, which lasts longer than 30 minutes and requires treatment.

Addressing parental anxiety forms a key part of the management of simple febrile seizures, because parents' (unspoken) worry with a first seizure is that their child might have died. However, there is little in the medical literature about this aspect of education and reassurance in the management of simple febrile seizures.

Etiology

Although the exact cause of simple febrile seizures is unknown, it is thought to be multifactorial, with genetic and environmental factors having been shown to contribute to its pathogenesis. Increasingly, a genetic predisposition is recognized, with febrile seizures occurring in families. However, the exact mode of inheritance is not known and seems to vary between families. Although polygenic inheritance is likely, there is a small number of families identified with an autosomal dominant pattern of inheritance of febrile seizures, leading to the description of a “febrile seizure susceptibility trait” with an autosomal dominant pattern of inheritance with reduced penetrance.

In addition, mutations in several genes have been found that account for enhanced susceptibility to febrile seizures. A familial epilepsy syndrome exists (generalized epilepsy with febrile seizures plus [GEFS+]), in which patients can have classic febrile seizures, febrile seizures that persist beyond five years (hence, the “FS+”), or epilepsy. Similar genetic factors have been identified that are involved in both febrile seizures and GEFS+.

Although the exact molecular mechanisms of febrile seizures are yet to be understood, underlying mutations have been found in genes encoding the sodium channel and the gamma-aminobutyric acid A receptor. Both of these channels are also associated with another early epilepsy syndrome, severe myoclonic epilepsy of infancy, which often begins with prolonged febrile seizure (either complex febrile seizure or febrile status) with subsequent seizures precipitated by fever.

With regard to risk factors, febrile seizures are more frequent in children attending day care centers, and in those with a first- or second-degree relative with a history of febrile seizures. The risk of another child having febrile seizures is one in five if one sibling is affected, and one in three if both parents and a previous child have had febrile seizures. Other risk factors associated with an increased rate of febrile seizure recurrence include young age at onset (younger than 12 months), history of simple or complex febrile seizures, and body temperature at onset of less than 40°C. Among these, age at onset seems the most constant predictive factor, with 50 percent of children younger than 12 months and 30 percent of children older than 12 months presenting with a recurrent febrile seizure. Positive family history of epilepsy is not consistently associated with an increased recurrence of simple febrile seizures.

Prognosis

The risk of developing epilepsy is increased in children with a history of complex febrile seizures. A strong association exists between febrile status epilepticus or febrile seizures characterized by focal symptoms and later development of temporal lobe epilepsy.