Typical febrile convulsions are:
- age 6 months to 6 years
- Normal neurodevelopment
- generalized, tonic-clonic
Most important differential is CNS infection eg encephalitis, meningitis. These tend to present with posturing, impaired conscious level, or focal seizures. 15% of patients presenting with status epilepticus with fever have meningitis (observational study) – although low rate of LP so underestimate? I suspect there would have been other features to suggest meningitis beforehand. Stiff neck? Fear of doing LP due to RICP from fit and/or meningitis, so do CT first if in ICU or abnormal neurology else as soon as no contraindication. If in doubt, treat empirically for meningitis (+/- herpes encephalitis, although risk unknown) with antibiotics and steroids. [Chin RFM, Arch Dis Child 2005;90:66-9.(Ed by Kneen)]
About 30-35% of febrile convulsions in the absence of CNS infection however have one or more complex features:
- focal onset,
- duration >10 minutes,
- or multiple seizures during the illness episode
Febrile status epilepticus, a subgroup of complex febrile convulsions with seizures lasting more than 30 minutes, occur in about 5% of cases. [BMJ 2015; 351 doi: http://dx.doi.org/10.1136/bmj.h4240 ]
Recurrence
One third of children with febrile convulsions will experience further seizures; age is the single, strongest, and most consistent risk factor. Most recurrences will occur during the first year and over 90% recur within two years (so unlikely to happen later). Other risk factors for recurrence are –
- family history of febrile convulsions (but not epilepsy) in a first degree relative,
- children whose initial seizure occurred with a relatively low fever,
- multiple initial seizures occurring during the same febrile episode.
Surprisingly, status in an otherwise normal child does not appear to significantly increase the risk for further febrile seizures or the development of epilepsy.
Subsequent Epilepsy
Following a first febrile convulsion, 2-4% of children will have an unprovoked ie afebrile seizure (4x risk in general population) and most of these children will subsequently develop epilepsy. Risk factors for epilepsy include –
- family history of epilepsy (not just febrile convulsions),
- atypical/complex features (as above),
- presence of early onset neurodevelopmental abnormalities (NB look for neurocutaneous syndromes eg neurofibromatosis, tuberosclerosis, Sturge-Weber syndrome). Febrile convulsions often first manifestation of Dravets syndrome, often prolonged, often partial.
There is clearly a genetic basis for febrile convulsions but complex, not a single gene defect. There is an association between prolonged febrile convulsions and mesial temporal sclerosis (pre-existing), but not specifically temporal lobe epilepsy.
No indication for EEG or anti-epileptic treatment in febrile convulsions – see SIGN 81.
Death
Risk of dying slightly raised for 2yr after febrile seizure but only for complex ie more than 15min duration or recurrent within 24hr (RR 1.99, but absolute risk v low).(Denmark, Lancet 08;372)
Information for Families
From European Journal of Pediatrics 2021:
