Febrile seizure
Exam Tips
- In OSCEs, classify explicitly: simple = generalised, <15 minutes, single in 24 hours, complete recovery <1 hour.
- State the emergency threshold clearly: any ongoing convulsive seizure at 5 minutes is treated as status epilepticus.
- Always mention red flags that force reconsideration of diagnosis: persistent altered consciousness, focal neurology, neck stiffness, petechiae/purpura, bulging fontanelle, or signs of raised ICP.
- Do not over-investigate a typical simple febrile seizure in a well child; focus investigations on source of fever and exclusion of CNS infection.
- Key counselling line for parents: antipyretics improve comfort but do not prevent seizure recurrence; teach first aid and when to call 999.
Definition
A febrile seizure is a seizure occurring in a child aged about 6 months to 5 years with fever (usually >38°C) and no evidence of central nervous system infection, acute metabolic disturbance, or prior afebrile epilepsy. It is classified as simple (generalised, <15 minutes, single in 24 hours, full recovery within 1 hour) or complex (focal features, >15 minutes, recurrent within 24 hours, or delayed recovery).
Pathophysiology
Febrile seizures are thought to result from an age-dependent hyperexcitability of the immature brain, where fever-related inflammatory mediators (for example IL-1β and other cytokine pathways) lower seizure threshold in genetically susceptible children. Susceptibility is polygenic in many cases, with familial clustering and overlap with fever-sensitive epilepsy syndromes (for example GEFS+ spectrum), while environmental triggers are mainly viral illnesses. High peak temperature is a stronger trigger than speed of temperature rise, and prolonged seizures risk excitotoxic injury, particularly in febrile status epilepticus (operational treatment threshold 5 minutes; higher risk of adverse sequelae with very prolonged duration). See Figure: simple vs complex febrile seizure classification and status timeline (5-minute treatment point vs 30-minute injury-risk point).
Risk Factors
- Family history of febrile seizures (first-degree relative)
- Age 6 months to 5 years (peak 12-18 months)
- High peak fever (often around or above 39°C)
- Viral febrile illness (for example HHV-6, influenza, RSV, adenovirus)
- Previous febrile seizure
- Short fever duration before seizure onset (<1 hour)
- Daycare attendance (higher viral exposure)
- Prematurity or pre-existing neurodevelopmental abnormality
- Possible iron deficiency (including iron deficiency anaemia)
- Maternal smoking in pregnancy
Clinical Features
Symptoms
- Witnessed convulsion during a febrile illness, often early in the illness
- Loss of consciousness with tonic then clonic limb movements (usually generalised in simple febrile seizure)
- Post-ictal sleepiness, irritability, or confusion
- Symptoms of underlying infection (coryza, cough, otalgia, dysuria, diarrhoea/vomiting)
Signs
- Measured fever or convincing parental report of fever
- Generalised tonic-clonic seizure activity in simple febrile seizure
- Possible focal motor signs, prolonged seizure, recurrence in 24 hours, or Todd's paresis in complex febrile seizure
- Transient cyanosis, pallor, frothing, or noisy breathing during the event
- Return to baseline neurology within 1 hour in simple febrile seizure
- Absence of meningeal signs or encephalopathic features if true uncomplicated febrile seizure
Investigations
Management
Lifestyle Modifications
- Immediate first aid: place child in recovery position, protect from injury, do not restrain, and do not put anything in the mouth
- Time the seizure and call emergency services if seizure lasts ≥5 minutes, repeats without recovery, or recovery is incomplete
- Treat fever for comfort, maintain hydration, and identify/treat the infection source
- Provide safety-net advice: recurrence risk is common, but most outcomes are good; teach carers home seizure first aid
- Continue routine childhood immunisations (small vaccine-associated seizure risk does not outweigh benefits)
Pharmacological Treatment
Rescue benzodiazepines for prolonged convulsive seizure/status
- Midazolam (buccal): 1 to <5 years 5 mg; 5 to <10 years 7.5 mg; 10 to <18 years 10 mg, single dose at 5 minutes
- Diazepam (rectal, alternative if buccal route unavailable): 0.5 mg/kg (usual max 10 mg in children)
- Lorazepam (IV in hospital): 0.1 mg/kg up to 4 mg per dose
Use when seizure is prolonged (operationally ≥5 minutes). Monitor airway and breathing closely due to risk of respiratory depression; seek urgent senior/paediatric support. If first dose fails, follow local paediatric status epilepticus protocol rather than repeated unsupervised community dosing.
Antipyretic symptomatic treatment
- Paracetamol oral: 15 mg/kg every 4-6 hours (max 4 doses in 24 hours)
- Ibuprofen oral: 5-10 mg/kg three times daily (max 30 mg/kg/day; avoid in dehydration/renal risk)
Antipyretics improve comfort but do not reliably prevent future febrile seizures. Avoid aspirin in under-16s (Reye syndrome risk).
Preventive antiepileptic therapy
Routine intermittent or continuous prophylaxis (for example diazepam/phenobarbital/valproate) is generally not recommended for typical febrile seizures because adverse effects outweigh benefit in most children.
Complications
- Recurrence of febrile seizures (about one-third after first episode)
- Febrile status epilepticus (important acute risk; prognosis worsens with longer seizure duration)
- Small increased long-term epilepsy risk (higher after complex febrile seizures)
- Parental/carer anxiety and reduced family quality of life
- Rare transient focal neurological deficit post-ictally (Todd's paresis)
Prognosis
Overall prognosis is excellent: most children have normal neurodevelopment and cognition after simple febrile seizures. Recurrence risk is approximately 32% (most within 1-2 years), increased by younger age at first seizure, family history, lower fever at onset, short fever duration before seizure, and multiple seizures in one illness. Later epilepsy risk is low after simple febrile seizure (around 1-2%) but higher after complex features (around 6-8%).
Sources & References
🏥BMJ Best Practice(4)
✅NICE Guidelines(1)
- Febrile seizure[overview]
📖Textbook References(2)
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 725, 726)[context]
- [Oxford Medical Handbooks] Ian Wilkinson, Tim Raine, Kate Wiles, Anna Goodhart, Catriona Ha - Oxford Handbook of Clinical Medicine (2017, Oxford University Press) - libgen.li.pdf(pp. 725)[context]