Key Facts

Febrile seizures are the most common seizure type in childhood. Parents should be reassured that simple febrile seizures are benign, do not cause brain damage, and have an excellent prognosis. The main clinical challenge is distinguishing febrile seizures from seizures caused by meningitis/encephalitis.

Epidemiology

Prevalence 2-5% of all children (higher in some populations — up to 8% in Japan). Peak incidence at 18 months. M:F 1.5:1. Strong genetic component — risk is 10-20% if first-degree relative affected. Most children have only one febrile seizure; ~30% have recurrence.

Aetiology

• Seizure occurs in the context of fever (≥38°C) from any cause (usually viral URTI, otitis media, UTI, roseola/HHV-6)
• NOT caused by CNS infection (meningitis/encephalitis must be excluded)
• Genetic predisposition: polygenic; FEB1-FEB8 loci identified; SCN1A mutations associated with severe forms
• The rapidly rising temperature rather than the absolute temperature is thought to be the key trigger

Pathophysiology

The immature brain (6 months-5 years) has a lower seizure threshold. Fever lowers this threshold further through: (1) enhanced neuronal excitability (temperature-dependent ion channel effects), (2) cytokine release (IL-1β), (3) altered GABA-A receptor function at elevated temperatures. The susceptibility resolves with brain maturation, hence the age-limited nature.

Simple Febrile Seizure (80%)

• Generalised tonic-clonic seizure
• Duration <15 minutes (usually <5 minutes)
• Single episode within 24-hour period
• No focal features
• Complete recovery within 1 hour
• Child developmentally normal

Complex Febrile Seizure (20%)

• Focal onset or features (one-sided jerking, eye deviation)
• Duration >15 minutes
• Multiple seizures within 24 hours
• Incomplete recovery within 1 hour
• Post-ictal neurological deficit (Todd's paresis)

Febrile Status Epilepticus

• Febrile seizure lasting >30 minutes (or >5 minutes by operational definition)
• Treat as per status epilepticus protocol

Red Flags (Exclude Meningitis/Encephalitis)

• Prolonged post-ictal state (>1 hour)
• Petechial/purpuric rash (meningococcal disease)
• Bulging fontanelle (infant — raised ICP)
• Neck stiffness (unreliable in <18 months)
• Persistent irritability/drowsiness after seizure resolves
• Complex features in child <18 months (low threshold for LP)

Simple Febrile Seizure

• No routine investigations needed (NICE CG160)
• Identify source of fever: clinical examination (ENT, urine dip, CXR if indicated)
• No EEG, no neuroimaging required for simple febrile seizures

Complex Febrile Seizure

• Bloods: FBC, CRP, U&Es, glucose, calcium, blood cultures (if unwell)
• Urine: MC&S (UTI is common occult source)
• LP: consider if <18 months with complex features (meningism unreliable); MUST perform LP if clinical suspicion of meningitis/encephalitis at any age
• EEG: not routinely indicated; consider if recurrent complex febrile seizures or concern for epilepsy
• MRI brain: consider if focal seizure, persistent neurological deficit, or developmental concerns

When to Perform LP (NICE CG160)

• Signs of meningitis/encephalitis at any age
• Child <18 months with complex febrile seizure
• Incomplete immunisation against Hib/meningococcus/pneumococcus
• Previously treated with antibiotics (may mask meningitis signs)

Acute Management

• Most febrile seizures stop spontaneously within 5 minutes — no intervention needed
• If seizure >5 minutes: buccal midazolam 0.3 mg/kg (or rectal diazepam 0.5 mg/kg) — parents of children with recurrent febrile seizures can be prescribed rescue midazolam
• Manage fever: paracetamol 15 mg/kg QDS or ibuprofen 5-10 mg/kg TDS (for comfort, NOT to prevent febrile seizures — antipyretics do NOT prevent recurrence)
• Identify and treat source of infection: antibiotics if bacterial infection identified

Parental Education and Reassurance

• Febrile seizures are common and benign (simple type)
• No brain damage occurs from simple febrile seizures
• Not epilepsy (though small increased risk)
• Recurrence: ~30% chance of another febrile seizure; does not mean child will develop epilepsy
• What to do if seizure occurs: stay calm, place child on side, do not restrain, note time, call 999 if >5 minutes

Prophylaxis

• Regular antipyretics do NOT prevent febrile seizures (multiple RCTs)
• Intermittent benzodiazepine prophylaxis: NOT routinely recommended; may be considered in exceptional circumstances (very frequent or prolonged febrile seizures) — oral clobazam during febrile illnesses
• Continuous AED prophylaxis: NOT recommended for febrile seizures (risks outweigh benefits)

Referral Criteria

• Paediatric assessment: all first febrile seizures should be assessed by a doctor (NICE CG160)
• Paediatric neurology: recurrent complex febrile seizures, developmental concerns, febrile status epilepticus, family history of epilepsy
• Admit: first febrile seizure in child <18 months, complex febrile seizure, febrile status epilepticus, unwell child, diagnostic uncertainty, social concerns

Simple febrile seizures: excellent prognosis. No long-term cognitive or developmental effects. Recurrence risk ~30% after first episode (higher if age <18 months, family history, low temperature threshold, short duration of fever before seizure). Epilepsy risk after simple febrile seizure: 1-2% (similar to general population). Complex febrile seizures: higher epilepsy risk (4-12%), particularly with focal features or prolonged duration. Febrile status epilepticus: associated with mesial temporal sclerosis and temporal lobe epilepsy (FEBSTAT study).

Simple vs Complex Febrile Seizure

Recurrence Risk Factors