Febrile seizures

Febrile seizures

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An 8 month old baby has been referred to you by the Accident and Emergency Department with the first episode of febrile convulsion. He has been coryzal over the last couple of days with spikes of temperature up to 38oC. The episode lasted for 5 minutes, the baby felt hot at the time and following recovery he has remained well.

Bottom line

  • Febrile seizures are benign in nature
  • They typically occur in children 6 months-6 years and they can be either simple or complex (duration > 15 minutes, multiple seizures over a 24 hour period, focal neurology).
  • The risk of recurrence is 30%
  • The risk of developing epilepsy following a simple febrile seizure is low but significantly higher with complex febrile seizures
  • There is no evidence for the use of regular antipyretics to prevent recurrence during an acute febrile episode
  • Part of the management is parental education on the management of future episodes at home and recognition of signs that the child needs urgent medical attention

 

What is a febrile seizure ?

A febrile convulsion is a seizure associated with fever (at least 38oC) in the absence of central nervous system infection or any electrolyte imbalance in a young child. By definition, febrile seizures occur in children between 6 months and 6 years of age. The median age of onset is 18 months and half of the children present between 12 and 30 months.

 

What are the features of a febrile seizure?

A simple febrile seizure is the most common type of febrile seizure (75%). It is usually a brief, generalised tonic-clonic seizure occurring with the onset of a rising temperature. In 87% of children, the duration of the febrile seizure is less than 10 minutes.

A complex febrile seizure is defined by at least one of the following criteria:

  • Duration of the seizure longer than 15 minutes
  • Multiple seizures within the last 24 hours
  • Presence of focal seizures

Febrile status epilepticus (> 30 minutes duration) occurs in only 5% of the paediatric population.

What is the cause of febrile seizures ?

The hypothalamus in the human brain is responsible for homeostatic core temperature regulation.  The hypothalamus is still developing in a young child and therefore it is more susceptible to straight rises in the body temperature. The febrile seizures represent the meeting point of low threshold for seizures and a trigger which is fever.

Mutations in sodium ion channel genes and neurotransmitter genes (e.g. gamma aminobutyric acid) have been identified in children with febrile seizures. These findings suggest the hypothesis of neuronal hyperexcitability to certain triggers.

Fever is the main trigger for febrile seizures. Viral infections are the main cause of fever. HHV-6 in roseola accounts for 20% of the cases presenting with the first episode of simple febrile seizures.

What is the risk of recurrence?

This is a commonly asked question by the parents. 30% of the children with a first episode of febrile convulsion will have a recurrence in the future. The following are risk factors associated with higher risk of recurrence:

  • Onset before the 18 months
  • Shorter duration of fever (<1 hour) before the onset of the seizure
  • Lower temperature close to 38oC
  • Family history of febrile seizures

What is the risk of epilepsy?

The vast majority of children presenting with febrile convulsion do not develop epilepsy.

The following are risk factors for developing afebrile seizures:

  • Complex febrile seizures
  • Presence of neurodevelopmental abnormality
  • Family history of epilepsy
  • Prolonged febrile seizures

Children with no risk factors have a 2.4% risk of developing afebrile seizures by the age of 25 compared with 1.4% percent for the general paediatric population. The risk is increased to 49% when all three component features of complex febrile convulsions are present. 

 

Investigations/Management

The investigations done on a child with fever should be directed by the severity of the illness and the suspected underlying condition.

For a child presenting with a simple febrile seizure and who is otherwise well, a careful history and a careful system examination should reveal the cause of infection. A urine sample should always be obtained to rule out urinary tract infection. Routine blood tests in children with simple febrile seizures is not recommended.

The following investigations should be considered in cases with diagnostic uncertainty or when the child appears to be unwell:

  • Routine blood testing for FBC, urea and electrolytes and CRP
  • CXR to look for evidence of chest infection
  • Lumbar puncture: if not contraindicated it should be performed as soon as possible when meningitis or encephalitis is suspected
  • Neuroimaging when focal neurology is present

When there is evidence of bacterial infection, antibiotic treatment should be given accordingly. When meningitis/encephalitis is suspected admission to the hospital is required for immediate commencement on intravenous antibiotics (ceftriaxone +/- acyclovir).


What advice should be given to parents?

The following advice should be given to parents :

The benign nature of the seizures

The risk of recurrence (30%)

The little evidence behind using antipyretic agents solely to keep temperature down or to prevent future episodes

Management of future episodes (placing the child in the lateral position, avoid forcing anything into the child’s mouth, ringing an emergency ambulance if seizure lasts for >5 minutes)

Explanation of signs and symptoms that would imply that the child is unwell (dehydration, petechial spots)

Explain the use of prophylactic diazepam and that this is very rarely needed

 

 

References

Lynette G Saddleir, Ingrid E Scheffer. Febrile seizures. BMJ 2007;334:307-311

Febrile Seizures, NICE Clinical Knowledge Summaries 2008

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About 

Dr Thanos Konstantinidis is a paediatric trainee in the North Western Deanery, England. Special interests include GlobalHealth, Medical Leadership, Paediatric Infectious diseases/immunology #NWSOP

4 Responses to "Febrile seizures"

  1. Simon Craig
    Simon Craig 3 years ago .Reply

    Nice post.
    I would disagree with the need to “always” perform a urine sample, though…

    • Thanos Konstantinidis
      Thanos Konstantinidis 3 years ago .Reply

      Hi thank you for your comment. A urine dipstick is obviously not needed when a child has a clear focus e.g lower respiratory tract infection. it can be useful as very often ,the presentation involves non specific symptoms such as lethargy , reduced feeding , ” being off colour ” . It also depends on the level of experience of the person who examines the child to determine the certainty for a certain focus of fever on a child who presents with such symptoms.

  2. Eric Jaeger
    Eric Jaeger 3 years ago .Reply

    I’m not sure the statement that febrile seizures occur “with the onset of a rising temperature” is supported by the literature.

    According to Saddlier et al. “No evidence exists that febrile seizures are more likely to occur with the maximal rate of temperature rise, although this is often quoted. Febrile seizures may occur before the fever is apparent and early or late in the course of a febrile illness.”

    I also think the generalization “Febrile seizures are benign in nature” is a dangerous one. While it is generally true, a small percentage of febrile seizures are status (5%) and these status seizures can indeed be quite dangerous. Quoting again from Saddleir et al.:

    Febrile status epilepticus (>30 minutes’ duration) occurs in 5% children and is more likely to have focal features. A prolonged febrile seizure is a risk factor for further prolonged attacks.

  3. Thanos Konstantinidis
    Thanos Konstantinidis 3 years ago .Reply

    Thank you very much for your reply. It is generally believed that febrile seizures are seizures accompanied by high temperature. It is true that there is lack of evidence suggesting a certain timing of the seizures in relation to the rate of temperature. There is substantial evidence indicating that the height of temperature plays a key role in eliciting seizures. As an accompanying feature, seizures may occur around the time of the temperature, despite the fact that the history that we often get from parents suggests an increasingly high temperature at the time of the seizure.
    Furthermore, febrile seizures are generally thought to be benign in nature as long as they are not associated with other worrying features. Duration of the seizure for more than 10 minutes is a feature that defines status. A patient ,presenting in such a way, will be treated in a way beyond the spectrum of a benign febrile convulsion. I am also not entirely sure, what the risk of a prolonged febrile seizures is increased with other co-morbidities such as underlying epilepsy, structural brain abnormalities, cerebral palsy etc.

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