Febrile convulsions
A rapidly rising temperature in an immature, seizure-prone brain can trigger a generalised seizure with no underlying intracranial cause, and the shape of the seizure (simple versus complex) is what predicts risk of recurrence and epilepsy, not the fever itself.
In a nutshell
A rapidly rising temperature can tip an immature, lower-threshold brain into a generalised seizure with no intracranial cause. Whether the seizure is simple (generalised, under 15 minutes, no recurrence) or complex (focal, prolonged, or recurrent) determines the risk of recurrence and epilepsy. The real clinical task is excluding a dangerous cause of fever-plus-seizure such as meningitis, then reassuring and safety-netting.
Classic presentation
An 18-month-old with a rapidly rising fever from a viral illness has a brief generalised tonic-clonic seizure, is drowsy afterwards, then returns fully to normal.
Key points
- Age 6 months to 6 years, and a rapidly rising temperature (not the peak) is the trigger in a susceptible, immature brain.
- Simple febrile convulsion: generalised, under 15 minutes, does not recur in the same illness (low recurrence and epilepsy risk).
- Complex febrile convulsion: focal, over 15 minutes, or recurs within 24 hours (higher recurrence and epilepsy risk), warrants closer follow-up.
- The critical differential is CNS infection: neck stiffness, bulging fontanelle, non-blanching rash, or failure to return to baseline should prompt urgent investigation, not reassurance.
- Anticonvulsants are not started after a first simple febrile convulsion: management is reassurance, treating the fever source, and safety-netting.
First-line investigation
Clinical assessment to identify the source of fever and to distinguish simple from complex febrile convulsion; further investigation (lumbar puncture, bloods) only if red flags for CNS infection are present.
First-line management
Basic seizure first aid and treatment of the underlying febrile illness, followed by parental reassurance and safety-netting rather than anticonvulsant prophylaxis.
Exam traps
- A febrile convulsion in a child under 6 months should not be assumed simple: CNS infection must be actively excluded.
- Antipyretics do not prevent febrile convulsions and are given for comfort only.
- A single simple febrile convulsion does not warrant starting long-term anticonvulsant medication.
- Focality or duration over 15 minutes reclassifies the seizure as complex, changing the risk profile and follow-up.
Educational content pending clinical review. Not medical advice.