Febrile Seizures
Febrile seizures are common in children aged 6 months – 5 years old. It peaks at 12 – 18 months. It is associated with temperatures higher than 38 C and is NOT the result of CNS infection or any other metabolic imbalance. It is benign and affects 3 – 5 % of children.
The risk of recurrence of febrile seizures is 30 – 50%. The risk fo recurrence of future epilepsy is 1% for simple febrile seizures and 6 – 20% for complex febrile seizures. Mortality rate for complex febrile seizures is 2 times higher for the next two years after seizure (probably due to the underlying etiology)
Febrile status epilepticus: a complex febrile seizure that lasts longer than 30 minutes or by shorter serial seizures, without regaining consciousness in the interictal state
Meyer’s hypothesis: the immature brain has enhanced excitatory neurotransmission (primarily glutamate-mediated) and underdeveloped inhibitory neurotransmission (mainly GABAergic). When a febrile illness causes a rapid rise in temperature, it further disrupts this balance, lowering the seizure threshold and leading to convulsions.
Simple vs Complex febrile seizure
| Simple febrile seizure | Complex febrile seizure | |
|---|---|---|
| Seizures per febrile episode | One | More than One |
| Duration | < 15 min | > 15 min |
| Characteristic | Generalized – tonic clonic | Focal or generalized, and prolonged |
| Recurrence | Does not recur in a 24 hour period | Recurs within a 24 hour period |
| Post-ictal phase | Short | Long and associated with deficits e.g. Todds palsy |
- Causes of febrile convulsions
- Infection with HHV 6
- Immunization with Measles or MMR or MMRV
- Iron deficiency (ferritin < 30 mcg/L)
- Genetics
- Sodium channel mutations
- GABA channel mutations
- Increased production of fever mediators
- Patient History
- Fever > 38 C
- No history of previous afebrile seizure
- Investigations
- Blood glucose
- Serum sodium: hyponatremia increases risk of recurrence (avoid hypotonic fluids)
- Lumbar puncture: if the infant is < 6 months or symptoms are suggestive of CNS infection.
- EEG: to differentiate non-vonvulsive status vs prolonged post-ictal state. Use only in high risk cases to develop epilepsy.
- Neuroimaging: in neurologically impaired child (fever provoked convulsions)
- Other investigations depend on the presentation of the child
- Treatment
- Admission
- Antipyretics (does not reduce risk of recurrence but increases comfort)
- Intermittent prophylaxis (clobazam) or continuous AED prophylaxis (valproate or phenobarbitone)
- For convulsions > 5 minutes
- Intranasal midazolam
- Rectal diazepam
- Risk factors for recurrence of febrile convulsions
- First episode (30%)
- Second episode (50%)
- Onset < 1 year of age (50%)
- Duration < 24 hours
- Fever 38 – 39 C (low degree of fever)
- Family history of febrile seizures or epilepsy
- Complex febrile seizure
- Daycare
- Male gender
- Low serum sodium at time of presentation
- Risk factors for future epilesy
- Simple febrile seizure (1%, like the general population)
- Recurrent febrile seizures (4%)
- Complex febrile seizure > 15 min in duration or recurrent within 24 hours (6%)
- Fever < 1 hour before feibrle seizure (11%)
- Family history of epilepsy (18%)
- Focal complex febrile seizure (29%)
- Neurodevelopmental abnormalities (33%)
