Febrile convulsion

From Ganfyd

AKA febrile seizure (FS).

Despite the straightforward name, a genetic syndrome of seizures associated with fever in the absence of central nervous infection or inflammation.

1. Simple
   • Seizure less than 15 minutes
   • Generalised
   • Does not reoccur in same febrile illness
2. Complex
   • Focal features
   • Prolonged past 15 minutes
   • Reoccurs with 24 hours

Usually a strong family history. Most common in children between 1 and 4 years of age, affecting between 2-5%, occasionally seen towards the end of the first year of life, and occasionally age 5-6 years.

Seizures usually occur early in the course of fever associated with an URTI, often with the first spike in temperature. They are tonic-clonic and generalized.

Prognosis

• Generally good

Recurrence

One third of children presenting with a febrile convulsion will have another one; age would appear to be the single, strongest, and most consistent risk factor: the younger you are when you have your first, the more likely you are to have another before you grow out of it! Most recurrences will occur during the first year after the initial episode and over 90% recur within two years. Other risks - family history of febrile seizures (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 epilepticus in an otherwise normal child does not appear to significantly increase the risk for further febrile seizures or the development of epilepsy.

Death

• Is very rare
• Long term mortality not increased but small excess mortality in first 2 years mainly associated with pre-existing neurological disease or those who develop true epilepsy^[1]

Associations

Following a first febrile convulsion, 2-4% of children will have an unprovoked (ie afebrile) seizure - this is 4x the risk in general population). Most of these children will subsequently develop epilepsy. Other risk factors for developing epilepsy:

• Family history of epilepsy
• Complex features
• Presence of early onset neurodevelopmental abnormalities

Genetic basis but multiple chromosomes, so complex and not strictly autosomal dominant. Current opinion supports an association between prolonged febrile convulsion and lesions in the temporal lobe (especially hippocampal sclerosis; in the past it was thought febrile convulsions might predispose to temporal lobe epilepsy, but the brain lesions probably pre-exists and increases the likelihood of febrile convulsion.

Assessment

No indication for EEG or anti-epileptic treatment in febrile convulsions - see SIGN 81.^[2]

Treatment

• Reassure carers

This is a common condition that although frightening for the family virtually never causes long term problems. Early use of antipyretics for fever seems sensible. Tepid sponging is no longer recommended, as it does not appear to offer any advantage over antipyretic medications. The commonly given advice to give anti-pyretic drugs to reduce fever in the hope of reducing the risk of febrile convulsion following childhood immunisation lacks good evidence of effectiveness^[3][4].

For children who present with a prolonged seizure, rectal diazepam to be used at home in the event of another prolonged (eg more than 5 minutes) seizure is an option.

Some children have frequent episodes, and although it is tempting to prescribe anti-epileptic medication to prevent stress and inconvenience, it is hard to justify the risk:benefit ratio.

References