Febrile seizure

Last revised by David Carroll on 3 May 2022

Febrile seizures are a largely idiopathic phenomenon which may occur between 6 and 60 months of age, defined by a seizure occurring concomitantly with a temperature over 38C (100.4F). This entity excludes seizures associated with infections of the central nervous system such as bacterial meningitis.


Febrile seizures are often referred to as "simple" or "complex" based on several features, with the former designation assigned if the following criteria are met:

  • absence of seizure recurrence within 24 hours 
  • return to prior neurologic baseline
  • seizure activity lasted for less than 15 minutes
  • seizure activity was "generalized" from onset 2
    • focal activity would be activity localized to e.g. one limb and would imply a pathologic epileptogenic focus

If one of the above was violated the episode is defined as a "complex" febrile seizure. Depending on the clinical context including factors such as age, recent antibiotics, and the presence or absence of abnormal features on the neurologic examination consideration may be made to pursue diagnostic imaging of the brain.


The peak incidence occurs around 18 months of age 3. A familial predilection has been incompletely described; over 25% of patients with febrile seizures have a family history of the same. 

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