Seizures, Febrile

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Febrile seizures occur in children aged 6 months to 5 years with fever ≥100.4°F (38°C) and absence of underlying neurologic abnormality, metabolic condition, or intracranial infection. Three distinct categories (1):

  • Simple febrile seizure (70–75%; must meet all criteria)
    • Generalized clonic or tonic–clonic seizure activity without focal features
    • Duration <15 minutes
    • Does not recur within 24 hours
    • Resolves spontaneously
    • No history of previous afebrile seizure or seizure disorder
  • Complex (CFS) (20–25%; only one criterion must be met)
    • Partial seizure, focal activity
    • Duration >15 minutes but <30 minutes
    • Recurrence within 24 hours
    • Postictal neurologic abnormalities (e.g., Todd paresis) (2)
  • Febrile status epilepticus (FSE) (5%)
    • Lasts >30 minutes


  • Approximately 500,000 febrile seizures occur in the United States annually.
  • Peak incidence is 18 months of age (2).
  • Only 6% of febrile seizures occur before age 6 months, and 4% of febrile seizures occur after age 3 years (3).
  • Bimodal seasonal pattern that mirrors peaks of febrile respiratory (November to January) and gastrointestinal infections (June to August) (2)

  • 2–5% of children in the white population aged 6 months to 3 years in United States and Western Europe (3)
  • Cumulative incidence varies in other populations (0.5–14%) (1).

Etiology and Pathophysiology

A variety of mechanisms have been proposed:

  • A lower baseline seizure threshold in the age group affected by febrile seizures
  • Familial genotypes may influence seizure thresholds.
  • Fever may alter ion channel activity, resulting in increased circuit excitability.
  • Cytokines released secondary to infection, specifically interleukin (IL)-1β, increase neuronal activity.
  • Evidence for genetic association:
    • Greater concordance in monozygotic than dizygotic twins
    • 25–40% of cases have positive family history (3).
    • Risk of febrile seizure with a previously affected sibling is increased.
    • Having two affected parents doubles a child’s risk of febrile seizure.
    • Mode of inheritance is multifactorial, although autosomal dominant inheritance reported (2).
  • Several rare familial epileptic syndromes present with febrile seizure.

Risk Factors

  • Any condition causing fever
  • Risk increases with the number of affected first-degree relatives.
  • Risk is increased for male children (1).
  • Recent vaccination
    • As febrile seizures are a benign entity, the benefits of vaccination outweigh the risk.
    • Possible increased risk with vaccinations, mainly MMR and DTaP, is a matter of much debate (3), and absolute vaccination-associated risk is very low.
  • Prenatal exposure to alcohol and tobacco, daycare attendance, premature birth, developmental delay, and prolonged NICU stay
  • Children with iron deficiency anemia may have increased risk for febrile seizures. Consider checking for anemia if the history suggests a risk for iron deficiency (4)[C].

General Prevention

Prevention is not usually indicated given the benign nature of this condition, lack of effective interventions, and side effects of prophylactic medications.

Commonly Associated Conditions

  • Viral infections: Common pathogens include human herpesvirus 6 (HHV-6), influenza, parainfluenza, adenovirus, and respiratory syncytial virus (RSV).
    • HHV-6 infection found in 30% of FSE in one study (3)
  • Bacterial infections: Frequently associated infections include otitis media, pharyngitis, urinary tract infection (UTI), pneumonia, and gastroenteritis (specifically with Shigella).

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