Febrile convulsions

Overview

•Most common childhood seizure type - affects 2-5% of children aged 6 months to 5 years (peak 12-18 months)

•Mechanism: rapid rise in temperature lowers seizure threshold in a developing (immature, more excitable) brain - the rate of rise matters more than the absolute temperature

•Common triggers: viral URTI, otitis media, roseola infantum (HHV-6), UTI

Classification

Simple vs complex febrile convulsion

Feature	Simple	Complex
Duration	<15 minutes	>15 minutes (or status ≥30 min; intervene at ≥5 min)
Seizure type	Generalised	Focal onset or focal features
Recurrence in 24 h	None	Recurs within same febrile illness
Recovery	Full recovery within 1 hour	Prolonged altered consciousness
Epilepsy risk	~1% (vs 0.5% general population)	4-6%

🎯

Operationally: treat any seizure lasting ≥5 minutes as status epilepticus and give rescue medication - do not wait for the 30-minute threshold.

Presentation

•Generalised tonic-clonic movements with fever >38°C - note any focal onset

•Post-ictal drowsiness expected; prolonged altered consciousness is a red flag

•Seizure often occurs at onset of illness before parents know child is febrile

•Examine for: meningism (neck stiffness, photophobia, Kernig's, Brudzinski's), non-blanching rash, conscious level

⚠️

In infants <18 months, meningism may be absent even with confirmed bacterial meningitis - maintain high suspicion regardless of examination findings.

Investigations

•Diagnosis is clinical - history and examination; investigations directed at identifying fever source and excluding differentials

🥇 First-line

•urine dipstick/culture (exclude UTI), blood glucose (exclude hypoglycaemia), FBC/CRP/blood cultures if CNS infection or sepsis suspected

•Lumbar puncture - if meningitis suspected; CT head first to exclude raised ICP (papilloedema, focal neurology, reduced GCS)

•If antibiotics already given, LP is especially important - meningism may be partially treated and masked

•EEG and MRI brain - not routinely indicated after simple febrile convulsion; arrange via paediatric neurology if epilepsy suspected

Differential diagnosis

•Bacterial meningitis / meningococcal disease - most important; non-blanching rash, meningism

•Viral encephalitis - altered consciousness, focal neurology

•Hypoglycaemia - check BM in all children with seizure

•Epilepsy - unprovoked seizures without fever

•Non-accidental injury - inconsistent history or unusual injuries

Management

•Acute seizure ≥5 min: rescue benzodiazepine - buccal midazolam (first-line in UK) or rectal diazepam

•Antipyretics (paracetamol, ibuprofen) - for comfort only; no evidence they prevent febrile convulsions from occurring or recurring

•Routine prophylactic anticonvulsants - not recommended for simple febrile convulsions

•Specialists may prescribe home rescue buccal midazolam or rectal diazepam with written plan for children with frequent/prolonged recurrences

•Parental education - essential; cover: what happened and why, excellent prognosis, no brain damage from typical episode, what to do if recurs (position, time, call 999 if >5 min), recurrence risk ~1 in 3, safety-netting symptoms (prolonged seizure, non-blanching rash, not recovering)

🎯

Antipyretics do NOT prevent febrile convulsions - a common exam trap. Do not advise aggressive fever reduction (tepid sponging, stripping) to prevent recurrence.

Prognosis

•Overall prognosis is excellent - normal development and cognition; condition is self-limiting as brain matures

•Recurrence rate: ~30%; higher risk if first seizure <18 months, complex first seizure, febrile status, short fever-to-seizure interval, family history

•Epilepsy risk: ~1% after simple febrile convulsion (vs 0.5% general population); 4-6% after complex febrile convulsions

•Recurrences virtually always cease by age 5

•Todd's paresis - transient focal hemiparesis post-seizure; resolves within 48 hours; not a sign of brain injury

💡

Simple febrile convulsions do NOT cause cognitive impairment, behavioural problems, or death - communicate this clearly to parents.