Febrile convulsions

Synonyms: febrile seizure, febrile fit

Definition^{1 2 3}

A febrile seizure can be defined as a seizure accompanied by fever (temperature higher than 38°C by any method), without central nervous system infection, which occurs in infants and children aged 6 months to 5 years.

Febrile seizures may be classified as simple or complex depending on the seizure duration, clinical features, and recurrence pattern:

• Simple febrile seizures are isolated, generalised, tonic-clonic seizures lasting less than 15 minutes, that do not recur within 24 hours or within the same febrile illness, with complete recovery within one hour.

• Complex febrile seizures have one or more of the following features: a partial (focal) seizure (movement limited to one side of the body or one limb); duration of more than 15 minutes; recurrence within 24 hours or within the same febrile illness; or incomplete recovery within one hour.

• Febrile status epilepticus describes a febrile seizure that lasts for 30 minutes or longer, or there are a series of seizures, without full recovery, lasting for 30 minutes or longer.

Other types of seizure related to acute illness in children are⁴ :

• Febrile myoclonic seizures⁵ .

• Afebrile convulsions in young children with mild gastroenteritis - clusters of seizures with/without fever over several days, in the setting of gastroenteritis. The prognosis is good.

Management of febrile seizures¹

Call an emergency ambulance if:

• 10 minutes after the first dose of rescue medication, the seizure has not stopped, the child has ongoing twitching or another seizure has begun before the child regains consciousness.

• There is suspected meningitis/meningococcal disease, encephalitis, or any other suspected serious or life-threatening cause of fever, such as pneumonia or sepsis.

Arrange immediate hospital assessment by a paediatrician if:

• It is the first presentation of febrile seizure (or a subsequent febrile seizure and the child has not had previous specialist assessment).

• The child is less than 18 months of age (clinical signs of central nervous system infection may be subtle or absent).

• There is uncertainty about the cause of the seizure.

• There are any features of a recurrent complex febrile seizure.

• There is any focal neurological deficit.

• There was a decreased level of consciousness prior to the seizure.

• The child has recently taken antibiotics (may mask the signs of central nervous system infection).

• There is parental/carer anxiety and/or difficulty coping.

Consider urgent hospital assessment for a period of observation if the child has unexplained fever and no apparent focus of infection.

Epidemiology¹

The reported prevalence varies depending on the definition used, the age of the child, the inclusion criteria, and the geographical region studied.

• Between 2% and 5% of European children have a febrile convulsion⁶ .

• Febrile seizures are the most common form of childhood seizure up to the age of 2 years.

• A UK study of 13,135 children followed up from birth to 5 years found 2.3% had febrile convulsions, and 20% of these presented with a complex febrile seizure.

• Febrile seizures are most common between 6 months and 6 years of age. Peak incidence is between 12-18 months of age. Onset is rare after 6 years of age.

• The male-to-female ratio is 1.6:1.

• Febrile status epilepticus occurs in about 5% of children who have febrile seizures.

Risk factors

About 50% of children who present with a febrile seizure have no identified risk factors. Known risk factors include:

• Family history of febrile seizure in first-degree relatives. The more relatives affected, the greater the risk. Susceptibility to febrile convulsions follows a multifactorial polygenic mode of inheritance with a maternal preponderance in transmission. There is a 27% risk in a child with an affected mother and 6% with an affected father.

• The peak temperature (rather than the speed of the temperature rise).

• Iron deficiency: studies have found that children with febrile seizures are more likely to be iron-deficient than age-matched controls⁷ .

Aetiology⁴

The mechanisms are unknown. It is uncertain whether the degree of fever or the rate of rise of temperature is a trigger in febrile seizures.

Genetic factors are involved: there is a family history of febrile seizures in 24%. Inheritance patterns are probably polygenic, although in a few families a particular gene or autosomal dominant inheritance has been identified.

Causes of fever in children with febrile seizures

The vast majority are:

• Viral infections

• Otitis media

• Tonsillitis

Other causes of fever with seizure are:

• Gastroenteritis

• Post-immunisation

Differential diagnosis¹

• Rigors.

• Syncope.

• Breath-holding spells.

• Reflex anoxic seizures - a precipitant (eg, a minor bump) causes vagally mediated cardiac asystole lasting many seconds - the child may be pale, floppy and lose consciousness, followed by tonic and clonic movements.

• Apnoea.

• Postictal fever (unlikely unless the seizure lasted >10 minutes; usually they would have a temperature >38°C).

• Other cause of seizures - eg, epilepsy, head injury, encephalitis, hypoglycaemia, hypocalcaemia, poisoning, other metabolic disorders, neurological disorders.

Assessment¹

History
Including:

• Eyewitness account of the seizure: conscious level prior to seizure, duration, focal or generalised, time taken to recover and state of the child afterwards.

• Symptoms of meningitis or septicaemia, such as: rapid onset of illness, abnormal behaviour or cry, stiffness or floppiness, vomiting, (and meningism in older children). Early symptoms are: leg pains, cold hands and feet, pallor or mottled skin⁸ .

• Establish whether it was a febrile seizure. This may be difficult to decide if the seizure occurs early in the illness. Parental perceptions of fever are valid.

• Past/family history of febrile seizure or epilepsy.

Examination

• Vital signs, conscious level, rash (blanching or non-blanching), fontanelle, meningism.

• Look for focus of infection.

NB:

• For babies and young children, clinical examination (more than history) is important in detecting serious illness. The vital signs are informative (temperature, pulse rate, respiratory rate and effort, capillary perfusion and oxygen saturation - compare with the normal range for the child's age)⁹ .

• The National Institute for Health and Care Excellence (NICE) traffic light system can help assess the likelihood of serious illness in a child aged under 5 with fever¹⁰ .

Hospital investigations^{4 11}

Initial investigations are according to the febrile illness rather than the seizure itself. These may include:

• Blood tests: FBC, erythrocyte sedimentation rate (ESR), glucose, U&E, coagulation, culture.

• Urine microscopy/culture if: age <18 months, complex seizure or no focus of infection found.

• LP should be considered for:
  

  • A child <12 months - LP advised unless a paediatric registrar decides against LP and will review within two hours.

  • A child 12-18 months - has a low threshold for LP.

  • Any 'serious features' (see details relating to hospital assessment above).

Further management¹

Children may be managed at home if:

• The child looks well.

• Parents understand how to treat febrile illness and further seizures, have prompt access to medical care and are happy with this plan (see 'Advice for parents', below).

Arrange review; the timing depends on the clinical condition - early review is advisable if the cause of fever is unclear.

Consider outpatient referral if:

• An alternative cause for seizures is suspected - eg, epilepsy or a neurodevelopmental condition.

• Parental request or concerns.

• The child has neurodevelopmental delay and/or signs of a neurocutaneous syndrome or metabolic disorder.

Advice for parents¹

Explanation is important, as seizures can be very frightening for parents. The following points should be covered and a leaflet provided:

• What febrile seizures are.

• How to treat fever at home - remove excess clothing, give fluids, give antipyretics if the child is uncomfortable. Tepid sponging or excessive cooling are not recommended. Check for a non-blanching rash, check for dehydration and stay with the child at night.

• First aid if the child has a fit - position; do not put anything in their mouth.

• When to call 999/112/911 ambulance - a seizure lasting more than five minutes.

• When and how to seek urgent medical advice - any seizure, serious symptoms such as non-blanching rash, lack of normal alertness, dehydration, the child getting worse, the parent worried and fever for more than five days.

Prognosis^{4 13}

Generally the prognosis is very good:

• By definition, febrile seizures do not recur beyond the age of 5 years approximately.

• There is no evidence for an increased risk of death, even for children with status epilepticus¹ .

• Intellect is not affected.

• Febrile seizures recur in about 30%.

• Risk factors for recurrence are: family history of febrile seizures, onset aged <18 months, lower temperature or shorter duration of fever at onset.

• Risk of epilepsy: 2-7% of children with febrile seizures will go on to develop epilepsy with afebrile seizures, the risk being higher with complicated febrile convulsions¹⁴ .

Prevention¹

• Immunisations do not appear to increase the risk of recurrent febrile seizures.

• There is no evidence that antipyretics reduce the number of febrile seizures¹⁰ .

• A Cochrane review found reduced recurrence rates for children with febrile seizures for intermittent diazepam and continuous phenobarbitone, with adverse effects in up to 30%. It was recommended that, given the benign nature of recurrent febrile seizures and the high prevalence of adverse effects of these drugs, parents and families should be supported with adequate contact details of medical services and information on recurrence, first aid management and, most importantly, the benign nature of the phenomenon¹⁵ .