Febrile Seizures
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Direct answer
A febrile seizure occurs with fever, without central nervous system infection or metabolic cause, between six months and five years — the commonest seizure disorder of childhood, affecting roughly 2 to 5 per cent. Simple febrile seizures — over two thirds — are generalised, last under 15 minutes, do not recur within 24 hours and leave no deficit; complex seizures have focal onset, duration over 15 minutes or recurrence within 24 hours. An acute seizure over five minutes is aborted with buccal or intranasal midazolam; routine imaging, EEG and continuous prophylaxis are not indicated, and epilepsy risk after a simple seizure is only 1 to 2 per cent.
What you must remember
- Simple: generalised, under 15 minutes, once in 24 hours, no focal features, no postictal weakness; complex: any one of focal semiology, over 15 minutes (febrile status at over 30 minutes), recurrence within 24 hours or a transient postictal paresis.
- The peak age is 14 to 18 months, the seizure typically on the first day of a viral fever — the rate of temperature rise matters more than its height.
- Recurrence risk overall 30 to 50 per cent, rising with young age at first seizure (under 12–15 months), family history of febrile seizures, low fever at the seizure and a short interval from fever onset — one risk factor roughly 30 per cent, four factors above 70 per cent.
- Epilepsy risk: about 1–2 per cent after a simple febrile seizure versus 5–10 per cent after a complex one, rising further with family history of epilepsy, neurodevelopmental abnormality or recurrent complex events.
- Lumbar puncture is not routine: perform it with meningeal signs, in an incompletely immunised infant aged 6 to 12 months, or when prior antibiotics may mask signs, per American Academy of Pediatrics guidance that Indian exams follow.
- MRI brain and EEG are not indicated after a simple febrile seizure; investigations should target the fever's cause.
- Acute management: lateral recovery position; a seizure over five minutes gets buccal or intranasal midazolam (roughly 0.2 mg/kg buccal) or rectal diazepam 0.5 mg/kg.
- Intermittent prophylaxis with oral clobazam or diazepam during febrile illness suits frequent recurrences; daily phenobarbitone or valproate is out of proportion to the risk.
- Genetic susceptibility is strong: a first-degree family history of febrile seizures is the most predictive item in the history.
A typical exam case
A 16-month-old boy has a two-minute generalised tonic-clonic seizure at the onset of a 39.2°C fever; by arrival he is drowsy but arousable, and within the hour he walks to his mother. First, confirm a simple febrile seizure by the four criteria — generalised, brief, single in the day, no focal features. Second, find the fever's source — otoscopy, throat and chest, with dengue and malaria smears in the Indian monsoon season. Third, decide against a lumbar puncture in a well, fully immunised child over 12 months, but tap if there is a bulging fontanelle, neck stiffness, petechiae or an unvaccinated infant. Fourth, counsel with numbers — recurrence risk, rescue midazolam beyond five minutes, and paracetamol for comfort, explicit that antipyretics do not prevent recurrence. Fifth, define the watch list: over 15 minutes, focal features, repeat seizures the same day or incomplete recovery — each converts simple to complex. The contrast case changes one variable: a focal 20-minute seizure demands exclusion of a structural cause and a fuller epilepsy-risk conversation.
High-yield viva angles
The first probe is usually the LP rule — when to tap a febrile-seizure child — and the answer is meningeal signs, age 6 to 12 months with incomplete immunisation, and prior antibiotics. The second is the recurrence arithmetic — the one-versus-four factor gradient, 30 to about 70 per cent. The third is prophylaxis: continuous phenobarbitone prevents recurrences at the cost of behaviour and cognitive change in a condition that rarely causes epilepsy — the standard of care is no daily drug. Finally, the febrile-status stem — a seizure over 30 minutes — is status epilepticus and gets the full protocol.
Frequently asked questions
What distinguishes a complex from a simple febrile seizure?
Focal onset, duration over 15 minutes, recurrence within 24 hours or postictal focal weakness — any single feature makes it complex.
What is the risk of epilepsy after febrile seizures?
About 1 to 2 per cent after a simple febrile seizure and 5 to 10 per cent after a complex one, higher still with family history of epilepsy or developmental abnormality.
Is continuous antiepileptic prophylaxis recommended?
No — the risks of daily phenobarbitone or valproate exceed the benefit; intermittent clobazam or diazepam during febrile illness is the compromise for frequent recurrences.
When is lumbar puncture indicated after a febrile seizure?
With meningeal signs, in incompletely immunised infants 6 to 12 months old, or when prior antibiotics could mask meningitis.
Do antipyretics prevent febrile seizure recurrence?
No — paracetamol and tepid sponging comfort the child but do not change recurrence risk, a key counselling point for families.