Description

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
  • Complex
    • 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

Epidemiology

• 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 to 24 hours after fever onset
  • ~20% >24 hours after fever onset

Risk Factors

• Positive family history of febrile seizures
• Prior febrile seizure (see “Prognosis” section)

General Prevention

• 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.

Pathophysiology

• 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.

Etiology

• Any viral or bacterial infection
  • Human herpesvirus 6 and 7
  • Influenza A
  • Shigellosis
• Vaccines
  • 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