• Clinical science

Febrile seizures

Abstract

Febrile seizures are one of the most common pediatric emergencies and are usually associated with high fever in children between six months and five years of age. The exact pathophysiology is unknown. Simple febrile seizures are the most common type; they are usually generalized, last under 15 minutes, and do not recur within 24 hours. Complex febrile seizures have a focal onset, last longer than 15 minutes, or recur within 24 hours. Diagnostic examination of simple febrile seizures focuses on addressing the cause of fever. Further diagnostics are required for patients with complex febrile seizures, particularly to exclude herpes encephalitis, and include lumbar puncture, CT scan, and/or EEG. Most febrile seizures end spontaneously and do not require any treatment. If seizures persist after five minutes or present as complex febrile seizures, however, IV benzodiazepines are the treatment of choice. Caregivers should be reassured as the prognosis of febrile seizures is good, with the risk of epilepsy being less than 10%.

Definition

Febrile seizures are seizures that are associated with fever; (mainly temperatures exceeding 38°C (100.4°F); ) in the absence of CNS infection, metabolic abnormalities, or a history of afebrile seizures.

References:[1][2][3]

Epidemiology

  • Peak incidence: : 2nd year of life; most commonly occurs between 6 months and 5 years of age
  • Prevalence: Febrile seizures occur in ∼ 4% of all children.

References:[4]

Epidemiological data refers to the US, unless otherwise specified.

Pathophysiology

The exact pathophysiological mechanisms of febrile seizures are not known. Risk factors:

  • Genetic predisposition
  • High fever (> 40°C (104°F))
  • Viral infection (e.g., HHV-6, influenza)
  • Recent immunization (especially MMR and TDap)

References:[1]

Clinical features

International League Against Epilepsy (ILAE) classification of febrile seizures

Simple febrile seizure (∼75%) Complex febrile seizure* (∼25%)
Clinical presentation
  • Focal onset
  • Pronounced on one side of the body
  • Transient hemiparesis and speech impairment
Duration and frequency
  • < 15 min
  • Maximum of one seizure within 24 h

Age

  • 6 months to 5 years

  • More commonly outside the typical range of 6 months to 5 years

Postictal phase
  • Typically a quick return to normal
  • Confusion and drowsiness may be present for a short period of time
  • Prolonged drowsiness or deviated eyes may be a sign of other etiology (e.g., meningitis) or of ongoing seizure activity (see status epilepticus)
*Febrile seizures are considered complex if at least one of the criteria are met!

References:[1][2]

Diagnostics

  • Approach
    • Simple febrile seizures do not require specific diagnostic workup
    • Diagnostic examination focuses on identifying the cause of fever
    • Complex febrile seizures always require specific investigative tests (e.g., EEG and imaging).
  • Determine the cause of fever
    • Physical examination
    • Urinalysis and urine cultures
    • Consider blood tests (CBC with differential blood, CRP, electrolytes, blood glucose)
    • Consider imaging to locate the source of infection (ultrasound, X-ray)
    • In suspected cases of intoxication: toxicology screen
  • Additional diagnostic steps: for complex febrile seizures and/or abnormal neurological examination

References:[1][2]

Differential diagnoses

Differential diagnoses of seizures
Febrile seizures Non-epileptic events or movements CNS infection (e.g., bacterial meningitis) Epilepsy
Findings
  • Chorea
    • Irregular, dance-like movements
  • Tremor
    • Rhythmic shaking of an extremity
  • Dystonia
    • Abnormal and uncoordinated contraction of muscle groups
  • Altered mental status
  • Petechial rash possible
  • Abnormal CSF findings (see differential diagnoses of meningitis)

The differential diagnoses listed here are not exhaustive.

Treatment

Uncomplicated seizures usually resolve after a few minutes spontaneously. However, abortive therapy should be administered if seizures ≥ 5 min or complex.

  • Abortive therapy
    • Treatment of choice: IV lorazepam
    • Alternative: IV diazepam , buccal/intranasal midazolam (when IV access is not possible)
    • If necessary, repeat medication after 5 min
    • Additional measures are needed with status epilepticus
    • Caregivers may administer rectal diazepam gel if seizures are prolonged while at home.
  • Reassure caregivers and provide information
  • After a febrile seizure, initiate antipyretic therapy (NSAIDs and acetaminophen) at an early stage (temperatures from 38°C (100.4°F)) as they restore the central thermoregulatory setpoint back to normal by reducing the synthesis of prostaglandin E2.

Febrile seizures primarily occur during the rise in temperature; therefore, prophylactic measures are often too late and a seizure cannot be prevented!

References:[3]

Prognosis

References:[2][5]