Febrile Seizures
Based on Nelson Textbook of Pediatrics, 21st Edition and recent updates
Table of Contents
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| febrile seizures definition |
Introduction
Febrile seizures are the most common seizure disorder in childhood, occurring in association with fever but without evidence of central nervous system infection or acute electrolyte imbalance. They represent a benign, age-limited condition affecting genetically predisposed children.
Epidemiology
Age group: 6 months to 5 years (peak: 12–18 months)
Incidence: ~2–5% of children in most populations
Recurrence rate: ~30–35% after first episode; higher in early onset (<1 year)
Family history: Positive in up to 25–40% cases, suggesting genetic susceptibility
Definition (Nelson)
A febrile seizure is defined as a seizure accompanied by fever (>38°C or 100.4°F), without evidence of CNS infection, metabolic abnormality, or a history of afebrile seizures.
Classification
1. Simple Febrile Seizure (SFS)
Generalized tonic-clonic in onset
Duration <15 minutes
Occurs once in 24 hours
No postictal neurological deficit
2. Complex (Atypical) Febrile Seizure (CFS)
Focal onset or focal features during/post seizure
Duration >15 minutes
Recurrent within 24 hours
May have postictal weakness (Todd’s paresis)
3. Febrile Status Epilepticus (FSE)
Febrile seizure lasting >30 minutes (or series lasting ≥30 min without full recovery)
Requires urgent management
Etiopathogenesis
Genetic predisposition:
Polygenic inheritance; linkage to FEB1–FEB11 loci (e.g., FEB4 on 5q14–q15)
GABRG2, SCN1A gene mutations implicated (especially when overlapping with GEFS+)
Fever and cytokine response:
Elevated IL-1β, IL-6, and TNF-α lower seizure threshold
Rapid temperature rise rather than peak temperature triggers seizure
Immature brain excitability:
Age-dependent increased neuronal excitability due to GABA-A receptor subunit composition and immature synaptic inhibition
Environmental factors:
Viral infections (HHV-6, HHV-7, influenza, adenovirus, parainfluenza)
Post-immunization (rare, within 24–72 hours, e.g., MMR)
Clinical Features
Typically occur within 24 hours of fever onset
Usually generalized tonic-clonic lasting <5 minutes
Postictal drowsiness but quick recovery
No signs of meningitis (neck stiffness, photophobia, etc.)
No pre-existing neurological abnormality
Evaluation
Goal: Exclude CNS infection, structural lesion, or metabolic cause.
History and examination:
Onset, duration, type of seizure
Timing relative to fever onset
Past neurological status, family history
Investigations:
Lumbar puncture:
Indicated if <12 months with incomplete immunization or signs of meningitis
Optional in 12–18 months if unclear
Not routinely needed in typical SFS
EEG:
Not indicated after first simple febrile seizure
Consider if complex, focal, or abnormal development
Neuroimaging:
Not indicated for simple FS
Consider MRI if focal deficits, prolonged seizures, or abnormal neurological findings
Serum electrolytes, calcium, glucose:
Only if atypical features or prolonged postictal state
Differential Diagnosis
| Condition | Distinguishing Feature |
|---|---|
| Meningitis/encephalitis | Signs of CNS infection, altered consciousness |
| Rigors | Consciousness maintained, no postictal phase |
| Epilepsy | Occurs without fever, may have preceding aura |
| Hypocalcemia, hypoglycemia | Biochemical abnormalities |
| CNS structural lesion | Focal deficits, developmental delay |
Management
Acute Episode
Ensure airway, breathing, circulation
Abort seizure if >5 minutes:
IV/rectal diazepam: 0.3–0.5 mg/kg
IV lorazepam: 0.1 mg/kg (max 4 mg)
IV midazolam (buccal/nasal): 0.2 mg/kg
Control fever:
Paracetamol 10–15 mg/kg/dose
Tepid sponging (avoid cold water)
Long-term Management
Antipyretics: No evidence they prevent recurrence
Intermittent prophylaxis:
Oral diazepam 0.3 mg/kg every 8 hr during febrile illness may reduce recurrence but causes sedation/ataxia
Used only in high-risk cases (e.g., frequent recurrent FS, high parental anxiety)
Continuous prophylaxis:
Phenobarbital or valproate previously used but not recommended due to adverse effects and limited benefit
Parental counseling:
Excellent prognosis
Not associated with brain damage, mental retardation, or epilepsy in most cases
2–7% risk of later epilepsy (higher if complex, family history, or abnormal neurodevelopment)
Educate about seizure first-aid: side positioning, not inserting objects in mouth, emergency use of rectal diazepam if >5 min
Prognosis
Recurrence risk factors:
Age <12 months at first episode
Family history of febrile seizure
Low-grade fever at first seizure onset
Short interval between fever onset and seizure
Epilepsy risk:
SFS: ~1–2%
CFS: up to 4–6%
FS with neurodevelopmental delay: up to 10%
Recent Updates (per Nelson & AAP guidelines)
Continuous anticonvulsant prophylaxis not recommended for either simple or complex FS
Intermittent diazepam during febrile illness may be used selectively
Vaccination-associated febrile seizures do not contraindicate further vaccination
Genetic studies indicate overlap between FS and GEFS+ (Generalized Epilepsy with Febrile Seizures Plus), suggesting a spectrum
Key Takeaways
Febrile seizures are benign, self-limited events related to fever in young children.
The mainstay of management is parental reassurance and acute seizure control, not long-term anticonvulsant therapy.
Investigations should focus on excluding CNS infection rather than diagnosing epilepsy.
References:
Kliegman RM, et al. Nelson Textbook of Pediatrics, 21st Edition, 2020.
American Academy of Pediatrics. Guidelines for the Neurodiagnostic Evaluation of the Child with a Simple Febrile Seizure. Pediatrics, 2011.
Shinnar S, et al. N Engl J Med, 2012;366:195–203.