Febrile seizure: seizure in ≤60-month-old child accompanied by a fever (≥100.4°F or 38°C by any method) but without central nervous system infection or prior unprovoked seizure (American Academy of Pediatrics [AAP] guidelines use 6 months as the lower age limit, whereas International League Against Epilepsy uses 1 month)

2 types:

  • Simple: febrile seizures that are generalized, last <15 minutes, AND do not recur in 24 hours
  • Complex
    • Febrile seizures that are focal (including postictal weakness), last ≥15 minutes, OR occur >1 time in 24 hours
    • Febrile status epilepticus: 1 febrile seizure or series of febrile seizures without full recovery in between lasting ≥30 minutes


  • Age
    • Most febrile seizures occur between 6 months and 3 years of age.
    • Peak age is about 18 months.
  • Type
    • 65–70% are simple febrile seizures.
    • 20–35% are complex febrile seizures.
    • ∼5% are febrile status epilepticus.
  • Timing of seizure
    • ∼20% before or <1 hour of fever onset
    • ∼60% 1–24 hours after fever onset
    • ∼20% >24 hours after fever onset


  • Most common childhood seizure
  • Febrile seizures occur in 2–5% of children in the United States and Western Europe, 9–10% of children in Japan, and 14% of children in Guam.

Risk Factors

Positive family history of febrile seizures


Usually multifactorial or polygenic inheritance

General Prevention

Antipyretics do not reduce the recurrence risk of simple febrile seizures.


  • Elevated temperatures in developing brain may increase neuronal excitability.
  • Fever increases cytokines that may enhance neuronal excitability.
  • Genetic factors
  • Hyperventilation from fever causes a respiratory alkalosis that may promote seizures.


  • Any viral or bacterial infection
    • Human herpesvirus 6 and 7
    • Influenza A
  • Vaccines
    • MMR(V) and DPT
    • Both increase the risk of febrile seizures but not epilepsy.
    • Benefits greatly outweigh any risk, and families should be encouraged to vaccinate.
  • Shigellosis

Commonly Associated Conditions

  • Generalized epilepsy with febrile seizures plus (GEFS+)
    • Febrile seizures beyond 6 years of age or afebrile seizures of varying types ranging from mild to severe
    • Multiple genes identified including SCN1A, SCN2A, SCN1B, GABRG2, GABRD, and PCDH19
  • Febrile infection–related epilepsy syndrome (FIRES)
    • Catastrophic epileptic encephalopathy of unknown etiology that begins with a febrile illness and refractory status epilepticus
    • Has high morbidity and mortality

There's more to see -- the rest of this topic is available only to subscribers.