Febrile convulsions

Synonyms: febrile seizure, febrile fit

What are febrile convulsions?^{1 2 3}

A febrile seizure or convulsion can be defined as a seizure which is:

• Accompanied by fever (temperature higher than 38°C by any method).

• Without intra-cranial infection, metabolic disturbance or other aetiology such as hypoglycaemia.

• Without a history of afebrile seizures.

• Present 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 are:

• Febrile myoclonic seizures.⁴

• 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:

• The seizure lasts for more than five minutes.

• 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.

How common are febrile seizures? (Epidemiology)
^{1 3}

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 children in Europe or the US have a febrile convulsion. In some countries (eg, Japan, Finland and the US) there is an association with season and time of day, with more episodes in the winter and in the afternoons.

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

• 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.

Causes and risk factors for febrile seizures⁵

About 50% of children who present with a febrile seizure have no identified risk factors; in these cases, the cause is unknown. It is thought that the immature brain responds to a high temperature by having a seizure, in a way that the adult brain doesn't, and that the trigger for this may be partly genetic predisposition and partly environmental factors.

The fever which triggers a convulsion may be from any cause including vaccination - febrile convulsions are less common after vaccination than after the infection for which we are vaccinating, and this risk does not change the fact that the benefits of vaccination vastly outweigh the risks.

Known risk factors include:

• Family history of febrile seizure or epilepsy in first-degree relatives.

• Some viral infections.

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

• Underlying neurological deficits or deficiencies in iron or zinc.

• Maternal smoking.

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.

Assessment^{1 6}

For babies and young children, clinical examination (more than history) is important in detecting serious illness, as the patient cannot give a history. Altered vital signs, such as tachycardia, can be a key sign of an unwell child. 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 fever.

History
This should include:

• An 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 skin.

• 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 due to the child feeling hot are valid; not all parents own a thermometer.

• Past/family history of febrile seizure or epilepsy.

Examination

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

• Look for a focus of infection, or signs suggesting another cause for the convulsion.

Hospital investigations

The choice of investigations will depend on the level of concern about the various differential diagnoses. Investigations may include those aimed at finding the focus of the infection (eg, urine or blood cultures), bloods to differentiate the severity of any infection (FBC, CRP), bloods to look for differential diagnosis (renal function, glucose) and more complex tests such as a lumbar puncture or imaging via CT or MRI.

Further management

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).

The timing of any review depends on the clinical condition.

Consider outpatient referral if:

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

• It is indicated due to parental concern.

• 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.

Prognosis⁷

Generally the prognosis is very good:

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

• There is no evidence for an increased risk of death, even for children with status epilepticus.¹

• 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 convulsions.⁸

Preventing febrile seizures¹

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

• There is no evidence that antipyretics reduce the number of febrile seizures.⁶

• A Cochrane review found that recurrence was reduced with the use of some anti-epileptic drugs, but adverse effects were high (up to 30%) - given the usually benign nature of febrile convulsions, such preventative medications should only be started by a specialist.⁹