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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.)
- Two types:
- Simple: febrile seizures that are generalized from the start, last <15 minutes, AND do not recur in 24 hours
- Febrile seizures that are focal (including postictal weakness), last ≥15 minutes, OR occur >1 time in 24 hours (simple febrile seizures plus—a proposed new category for those whose only complex feature is >1 seizure in 24 hours)
- Febrile status epilepticus: one febrile seizure or series of febrile seizures without full recovery in between lasting ≥30 minutes
- Most febrile seizures occur between 6 months and 3 years of age.
- Peak age is about 18 months.
- 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 to 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.
- Positive family history of febrile seizures
- Prior febrile seizure (see “Prognosis” section)
Usually multifactorial or polygenic inheritance
- Antipyretics do not reduce the recurrence risk of simple febrile seizures.
- Very low risk of febrile seizure after some vaccinations, for example, DPT, influenza and MMR(V)
- Nonetheless, routine childhood immunizations are recommended, as the morbidity of vaccine-preventable illnesses outweighs the risk of febrile seizures.
- Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP) does not list febrile seizures as a contraindication to any commonly used vaccine; seizures ≤3 days after a previous dose of DTP/DTaP is listed as a precaution for future doses.
- 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
- Influenza, DPT, and MMR(V)
- These may increase the risk of febrile seizures but not epilepsy.
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
- High morbidity and mortality