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