Febrile Seizures

Introduction

A febrile seizure is a seizure (convulsion) which occurs in a febrile child (between the ages of 6 months and 5 years) and is not caused by a central nervous system infection.¹

Febrile seizures are the most common cause of seizures in children, with 1 in 20 children having a febrile seizure at some point.¹

Aetiology

The exact aetiology of febrile seizures is unknown. They are considered an age-dependent response of the immature brain to fever, with a multifactorial mix of genetic and environmental factors.¹

80% of febrile seizures are caused by viral infections, with human herpesvirus 6 and influenza being the most common infections.¹

Risk factors

Risk factors for febrile seizures include:

• Family history of febrile seizures
• High fever (>40°C)
• Viral infection (influenza, chickenpox, etc)
• Recent immunisation (rare)

Around 50% of children who present with a febrile seizure have no identified risk factor.²

Clinical features

Most febrile seizures occur within 24 hours of the child developing a fever. The parents may give a history of a previously well child who developed a high temperature and started convulsing.

The clinical features will vary depending on the type of febrile seizure. 

Simple febrile seizures

80-85% of children will have a simple febrile seizure. Clinical features of a simple febrile seizure include:³

• Duration of fewer than 15 minutes (most last <5 minutes)
• Generalised seizure (symmetrical and involving the whole body)
• Occur only once in 24 hours (i.e. not recurrent seizures)

Simple febrile seizures are usually tonic-clonic in nature, with episodes of limb stiffening and jerking. There may be tongue biting and incontinence during the episode. Parents may also describe abnormal eye movements (e.g. eyes rolling back). 

The post-ictal phase for a simple febrile seizure is usually less than one hour. A longer post-ictal state with excessive drowsiness or confusion should raise suspicion of central nervous system infection or status epilepticus.

Prolonged recovery from a febrile seizure (>1 hour) is more suggestive of a complex febrile seizure.⁴

Complex febrile seizures

15-20% of children will have complex febrile seizures. Clinical features of a complex febrile seizure include at least one of the :

• Duration of longer than 15 minutes
• Focal seizure
• Prolonged postictal state (more than 1 hour to achieve complete recovery )
• More than one seizure in 24 hours

Children with complex seizures tend to be younger and are more likely to have developmental delays.³

A seizure lasting more than 30 minutes, or multiple seizures without recovery is febrile status epilepticus. 

Identifying the source of fever

A thorough clinical examination should be performed to identify the source of the fever. This should include examination of the ear, nose and throat, respiratory examination, and general inspection for rashes.  

It is important to exclude a sinister cause of the seizure (e.g. meningitis). 

Differential diagnoses

Table 1. Differential diagnoses to consider in the context of a suspected febrile seizure. 

Investigations

Children with simple febrile seizures, who rapidly recover and are otherwise well, require no investigations following a febrile seizure.¹ 

It is important to exclude hypoglycaemia in an actively seizing child or if there is a prolonged recovery period. 

Management

Immediate management of a seizure

Most febrile seizures will have resolved at the time of presentation to healthcare services. 

For more information on the immediate management of seizures, see the Geeky Medics guide to the acute management of seizures.

Management following the seizure

The clinical assessment following a simple febrile seizure should focus on finding the source of fever in the child.

If there is suspicion of a central nervous system infection or other life-threatening cause of a fever, arrange an emergency hospital admission.

Generally, assessment by the paediatric team is required for the following situations:

• First febrile seizure
• Children under 18 months old
• Uncertain diagnosis
• Recent antibiotic use
• Decreased level of consciousness before the seizure
• Focal neurological deficits
• Recurrent or complex seizures

Children with developmental delay and/or symptoms of neurocutaneous or metabolic disorders be referred to a paediatric neurologist.¹ 

Parental education

Parents can be very distressed after witnessing a febrile seizure.

It is important to explain the benign nature of febrile seizures, the difference between febrile seizures and epilepsy, the chance of a child having another febrile seizure and the natural history of febrile seizures. 

Parents and caregivers should be given information on managing seizures, including basic first aid measures (e.g. the recovery position) and when to call for emergency help.

Written information including patient information leaflets, first aid instructions and a personalised seizure plan should be given to parents. If they have been given rescue medication (e.g. buccal midazolam) by a specialist, they should be shown how and when to administer it.²

Complications

Complications of febrile seizures include:

• Injury while seizing 
• Aspiration while seizing 
• Small increased risk of epilepsy as compared to the general population 
• Risk of recurrence 

The prognosis of febrile seizures is good and seizures usually stop by the age of 5 – 7.

One-third of children will have a recurrence of a febrile seizure. Risk factors for recurrence include a family history of febrile seizures, onset aged <18 months, lower temperature, or shorter duration of fever at the onset.

Key points

• A febrile seizure is a seizure (convulsion) which occurs in a febrile child (between the ages of 6 months and 5 years) and is not caused by a central nervous system infection.
• Most children have simple febrile seizures which are short (<15 minutes ), generalised, have a short postictal period, and occur only once in 24 hours.
• Complex febrile seizures are longer (>15 minutes), focal, have a long postictal period, and may reoccur within 24 hours.
• It is important to rule out a sinister cause of seizures in a child with fever and seizures (e.g. CNS infection).
• Most febrile seizures are benign and do not lead to long-term neurological damage or intellectual disability.
• Parents should be taught how to manage a seizing child and when to call an ambulance. 
• There is a small increase in the chances of developing epilepsy later in life. The risk depends on the kind of seizure the child has and the family history of epilepsy.

Reviewer

Dr Sanjay Gupta

Consultant Paediatrician

Editor

Dr Chris Jefferies

References

1. NICE Clinical Knowledge Summary. Febrile Seizures. Available from: [LINK] 
2. StatPearls. Febrile Seizure. Available from: [LINK]
3. BMJ Best Practice. Febrile Seizures. Available from: [LINK] 
4. NHS Choices. Febrile Seizures. Available from: [LINK] 
5. Patient.info Febrile Convulsions. What Causes Febrile Convulsions. Available from: [LINK]