Febrile Seizures
Febrile seizures are the most common seizure type in children, occurring between 6 months and 5 years during febrile illness. Simple febrile seizures are benign with excellent prognosis and no increased risk of epilepsy.
Key Facts
Febrile seizures affect approximately 2-5% of children aged 6 months to 5 years Simple febrile seizure: Generalised tonic-clonic, duration <15 min, single episode in 24h, complete recovery within 1 hour — most common type (~70-80%) Complex febrile seizure: Focal features, duration >15 min, recurs within 24h, or incomplete recovery — requires more investigation Risk of epilepsy: ~1% after simple febrile seizure (vs ~1% in general population); ~4-6% after complex febrile seizure Recurrence risk: ~30% overall; higher if: first seizure <18 months, family history, low-grade fever at seizure onset Investigations: NOT routinely needed for simple febrile seizure — focus on identifying and treating the source of fever LP: Consider if <12 months (meningism may be absent); perform if signs of meningitis; consider if complex or prolonged Antipyretics (paracetamol/ibuprofen) do NOT prevent febrile seizures — but should be used for child's comfort
Overview
Key Facts
Febrile seizures are benign convulsions triggered by fever in developmentally normal children. They are one of the most frightening experiences for parents but carry an excellent prognosis. The key role of the clinician is to identify and treat the source of fever, exclude meningitis, and provide parental reassurance.
Epidemiology
Febrile seizures affect 2-5% of children between 6 months and 5 years. Peak incidence: 18 months. Boys are slightly more commonly affected. ~30% recur. Family history is common (polygenic inheritance).
Aetiology
- Febrile seizures occur during a rapid rise in temperature, usually >38°C
- Most common triggers: Viral URTIs, otitis media, UTI, roseola (HHV-6 — classic cause)
- NOT caused by: Intracranial infection (by definition — must exclude meningitis/encephalitis)
- Genetic predisposition: Polygenic; family history in ~25-40%
Pathophysiology
The immature brain has a lower seizure threshold. Fever increases neuronal excitability through temperature-dependent ion channel changes and inflammatory cytokines (IL-1β, TNF-α). The mechanism is NOT simply the height of fever but likely relates to the rate of temperature rise and individual genetic susceptibility.
Clinical Presentation
Simple Febrile Seizure (70-80%)
- Generalised tonic-clonic
- Duration <15 minutes (usually <5 min)
- Single episode in 24-hour period
- Complete recovery within 1 hour
- Age 6 months to 5 years
- Developmentally normal child
Complex Febrile Seizure (20-30%)
- Focal features (one-sided movements, eye deviation)
- Duration >15 minutes
- Recurs within 24 hours
- Incomplete recovery (prolonged drowsiness, focal weakness — Todd's paresis)
Red Flags
- Signs of meningitis (neck stiffness, bulging fontanelle, non-blanching rash, photophobia)
- Prolonged seizure >5 min — treat with buccal midazolam as per status epilepticus protocol
- Developmental concerns — may indicate underlying neurological condition
- Very young infant (<6 months) — lower threshold for investigation including LP
- Repeated complex febrile seizures — consider underlying epilepsy syndrome
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Simple febrile seizure | Generalised, <15 min, single, full recovery, 6mo-5yr | Clinical; find fever source |
| Complex febrile seizure | Focal, prolonged, recurrent, incomplete recovery | Consider LP, EEG, MRI |
| Meningitis/encephalitis | Neck stiffness, altered consciousness, rash, focal signs | LP, blood cultures, CT |
| Epilepsy | Afebrile seizures, recurrent, developmental concerns | EEG, MRI |
| Rigor | Shivering (not rhythmic jerking), conscious throughout | Clinical |
| Breath-holding attack | Provoked by crying/upset, colour change, brief LOC | Clinical |
Diagnosis / Investigation
Simple Febrile Seizure
- No routine investigations required — clinical diagnosis
- Identify and treat source of fever (examine ears, throat, chest, urine)
- Urine MC&S: Recommended (UTI is a common occult source in young children)
Complex Febrile Seizure
- Consider LP: If <12 months, signs of meningitis, or not fully recovered
- Blood glucose: Post-seizure
- U&Es, blood culture, FBC: If systemically unwell
- EEG: Not routine; consider if recurrent complex febrile seizures
- MRI brain: Not routine; consider if focal or recurrent complex seizures
When to LP
- Signs of meningitis
- Age <12 months (meningism may be absent)
- Complex febrile seizure with incomplete recovery
- Not immunised against Hib or meningococcus
Management
Acute Seizure (>5 Minutes)
- Buccal midazolam 0.5mg/kg (max 10mg) — parents should have emergency medication if recurrent
- Rectal diazepam 0.5mg/kg: Alternative if buccal midazolam not available
- Follow APLS status epilepticus protocol if not terminating
Post-Seizure
- Recovery position: Once seizure stops
- Identify and treat fever source: Antibiotics if bacterial infection identified
- Paracetamol/ibuprofen: For comfort — but do NOT prevent febrile seizures
Non-pharmacological
- Parental education: Reassure about excellent prognosis; explain what to do if seizure recurs (place on side, time seizure, call ambulance if >5 min)
- No prophylactic anticonvulsants: NOT recommended for simple febrile seizures
- Emergency medication plan: Consider buccal midazolam for parents of children with recurrent prolonged febrile seizures
Referral Criteria
- Complex febrile seizure — paediatric assessment
- Recurrent febrile seizures (>3) — paediatric neurology consideration
- Developmental concerns — community paediatrics
- Febrile status epilepticus (>30 min) — neurology follow-up
Prognosis
- Recurrence: ~30% after first; ~50% after second; highest risk if <18 months at first seizure
- Epilepsy risk: Simple FS → ~1% (same as general population); complex FS → ~4-6%
- Neurodevelopmental outcome: NO adverse effect on cognition, behaviour, or academic performance
- Duration: Most last <5 minutes; self-limiting
- Mortality: Essentially zero from the seizure itself
Other Relevant Information
Simple vs Complex Febrile Seizure
| Feature | Simple | Complex |
|---|---|---|
| Type | Generalised | Focal features |
| Duration | <15 min | >15 min |
| Frequency | Single in 24h | Recurs within 24h |
| Recovery | Complete within 1h | Incomplete |
| Investigation | Find fever source | Consider LP, EEG, MRI |
| Epilepsy risk | ~1% | ~4-6% |
Recurrence Risk Factors
| Factor | Increases Risk |
|---|---|
| Age <18 months at first seizure | Yes |
| Family history of febrile seizures | Yes |
| Low-grade fever at seizure onset | Yes |
| Short duration of fever before seizure | Yes |
| Frequent febrile illnesses | Yes |