Febrile Seizures

Updated: Sep 19, 2017
  • Author: Nooruddin R Tejani, MD; Chief Editor: Kirsten A Bechtel, MD  more...
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Febrile seizures are the most common type of seizures observed in the pediatric age group.

Although described by the ancient Greeks, it was not until this century that febrile seizures were recognized as a distinct syndrome separate from epilepsy. In 1980, a consensus conference held by the National Institutes of Health described a febrile seizure as, "An event in infancy or childhood usually occurring between three months and five years of age, associated with fever, but without evidence of intracranial infection or defined cause." [1] It does not exclude children with prior neurological impairment and neither provides specific temperature criteria nor defines a "seizure." Another definition from the International League Against Epilepsy (ILAE) is "a seizure occurring in childhood after 1 month of age associated with a febrile illness not caused by an infection of the central nervous system (CNS), without previous neonatal seizures or a previous unprovoked seizure, and not meeting the criteria for other acute symptomatic seizures." [2]

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Febrile seizures occur in young children at a time in their development when the seizure threshold is low. This is a time when young children are susceptible to frequent childhood infections such as upper respiratory infection, otitis media, viral syndrome, and they respond with comparably higher temperatures. Animal studies suggest a possible role of endogenous pyrogens, such as interleukin 1beta, that, by increasing neuronal excitability, may link fever and seizure activity. [3] Preliminary studies in children appear to support the hypothesis that the cytokine network is activated and may have a role in the pathogenesis of febrile seizures, but the precise clinical and pathological significance of these observations is not yet clear. [4, 5]

Febrile seizures are divided into 2 types: simple febrile seizures (which are generalized, last < 15 min and do not recur within 24 h) and complex febrile seizures (which are prolonged, recur more than once in 24 h, or are focal). [6] Complex febrile seizures may indicate a more serious disease process, such as meningitis, abscess, or encephalitis. Febrile status epilepticus, a severe type of complex febrile seizure, is defined as single seizure or series of seizures without interim recovery lasting at least 30 minutes.

Viral illnesses are the predominant cause of febrile seizures. Recent literature documented the presence of human herpes simplex virus 6 (HHSV-6) as the etiologic agent in roseola in about 20% of a group of patients presenting with their first febrile seizures. Shigella gastroenteritis also has been associated with febrile seizures. One study suggests a relationship between recurrent febrile seizures and influenza A. [7, 8]

Febrile seizures tend to occur in families. In a child with febrile seizure, the risk of febrile seizure is 10% for the sibling and almost 50% for the sibling if a parent has febrile seizures as well. Although clear evidence exists for a genetic basis of febrile seizures, the mode of inheritance is unclear. [9]

While polygenic inheritance is likely, a small number of families are 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. 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 amino-butyric acid A receptor. [10, 11, 12]




United States

Between 2% and 5% of children have febrile seizures by their fifth birthday. [13]


A similar rate of febrile seizures is found in Western Europe. The incidence elsewhere in the world varies between 5% and 10% for India, 8.8% for Japan, 14% for Guam, [14] 0.35% for Hong Kong, and 0.5-1.5% for China. [15]


Children with simple febrile seizures do not have increased mortality risk. However, seizures that were complex, occurred before age 1 year, or were triggered by a temperature of less than 39°C were associated with a 2-fold increased mortality rate during the first 2 years after seizure occurrence. [16]

Children with febrile seizures have a slightly higher incidence of epilepsy compared with the general population (2% vs 1%). Risk factors for epilepsy later in life include complex febrile seizure, family history of epilepsy or neurologic abnormality, and developmental delay. Patients with 2 risk factors have up to a 10% chance of developing afebrile seizures. [17, 18]


Febrile seizures occur in all races.


Some studies demonstrate a slight male predominance.


By definition, febrile seizures occur in children aged 3 months to 5 years.