Febrile seizures

• A febrile seizure is a convulsion caused by fever in a child aged six months to five years, with no infection of the central nervous system; it is the commonest convulsive event of childhood. ^[6]
• Most are simple - generalised, brief, and single - and most children grow out of them by school age, with no effect on intelligence or behaviour. ^[1]
• Classification is the decision that drives everything: simple seizures need little testing and a lot of reassurance; complex seizures need more careful evaluation for meningitis and other causes. ^[1][5]
• For a seizure that lasts more than five minutes, give a benzodiazepine; nothing else in drug therapy is routinely recommended, because both antiepileptic drugs and ordinary antipyretics have not been shown to prevent further febrile seizures. ^[1][2][4]
• Parents need practical first-aid advice and a realistic recurrence figure, not panic; that is the treatment. ^[1]

By the end of this page you should be able to:

1. Define a febrile seizure and separate a simple from a complex one.
2. Explain who is most at risk, why fever triggers the seizure, and how the fever relates to the seizure.
3. Take a targeted history and examination, and state when a lumbar puncture, brain imaging or EEG is justified and when it is not.
4. Manage an active seizure safely with oxygenation, measurement of blood glucose, and the right benzodiazepine.
5. Counsel a family with an honest but reassuring account of recurrence and epilepsy risk, including when to seek emergency help.
6. Work through an approach that is safe when you do not have immediate access to tests or medicines.

The word "febrile" refers to fever, "convulsion" to the visible shaking. The key qualifier is the absence of central nervous system infection: find meningitis at this age and the event is no longer a febrile seizure, it is a seizure due to meningitis. ^[1]

Classification is made only after the event, from the history and examination. A seizure is simple only if it satisfies all four of these features: it lasts less than 15 minutes, is generalised from the start, occurs once in any 24 hour period, and the child has no previous neurological problem. ^[1][6] If any one of the following is present, the seizure is complex: it lasts 15 minutes or more, it begins focally or shows focal features during or after the event, or it recurs within the same 24 hours. ^[1] A child with more than one complex feature is at materially higher risk of later unprovoked seizures, so counting the features matters. ^[1]

A seizure should not be labelled febrile at all if it occurs outside the 6 to 60 month age range, if the child is neurologically abnormal, or if the fever is caused by meningitis or encephalitis: these are all outside the definition. ^[1][6]

Febrile seizures are the most common seizure disorder of childhood. They affect 2 to 5 percent of children between six and 60 months of age. ^[6] In the United Kingdom and the United States they are reported in about 2 to 4 percent of children. ^[4] About one child in three who has a first febrile seizure will have another during childhood. ^[4] The peak incidence is in the second year of life, which is the period in which the brain is most sensitive to fever and viral infection. ^[1]

Other than age, the main risk factors are exposure to the viral illnesses of early childhood, a family history of febrile seizures, conditions of prematurity or prolonged neonatal care, developmental delay, and attendance at day care. ^[1] The height of the fever matters more than how quickly it rises: the seizure threshold varies from child to child and falls as temperature climbs. ^[1]

Males and females are affected about equally. In regions with high rates of incomplete immunisation against Haemophilus influenzae type b and Streptococcus pneumoniae, bacterial meningitis remains a much more important differential, and that alters both the evaluation and the threshold for lumbar puncture. ^[1][5]

Febrile seizures have no single cause. They arise in a child whose nervous system is at a vulnerable stage of development, under the stress of a fever. Viral illnesses, particularly those producing high fever, are the usual provocation: human herpesvirus 6, influenza, adenovirus and parainfluenza are the viruses most strongly associated. ^[1] Because high fever increases neuronal excitability and lowers the seizure threshold, the illness rather than the pathogen is what triggers the event. ^[1]

Genetic susceptibility is well documented. A first-degree relative with febrile seizures carries an odds ratio of about 4.5, and a second-degree relative about 3.6. ^[1] Several familial epilepsy-syndrome genes also increase the risk of febrile seizures, and individual susceptibility is probably polygenic. ^[1] There is no known modifiable risk factor for the febrile seizure itself.

Vaccination deserves explicit discussion because families often worry about it. The measles-mumps-rubella vaccine is associated with an excess risk of around 10 febrile seizures per 10 000 children vaccinated at 16 to 23 months, and around 4 per 10 000 vaccinated at the recommended 12 to 15 months. ^[1] The combined measles-mumps-rubella-varicella vaccine adds around 3.5 excess cases per 10 000 compared with giving the two vaccines separately. ^[1] The influenza and modern acellular pertussis vaccines do not increase risk meaningfully. ^[1] Standard vaccine-preventable infection carries a far greater seizure risk than the vaccine does, and children should receive all routine immunisations on schedule. ^[1] Antipyretics given after vaccination do not prevent febrile seizures and may reduce the antibody response, so they should not be given routinely for that purpose. ^[1]

Other risk factors include maternal smoking or heavy stress in pregnancy, neonatal intensive care for more than 28 days, developmental delay and day-care attendance. ^[1]

The sequence is the same in every febrile seizure, and understanding it explains why the event is usually benign. An infectious or inflammatory illness raises core temperature. Fever-responsive changes in ion channels and in neurotransmitter balance make the infant brain hyperexcitable, and the particular brain of a child aged six months to five years is unusually prone to synchronised discharges at those temperatures. ^[1] The result is a generalised convulsion. It is driven by the fever, not by infection of the brain, and it stops as the cerebral substrate recovers, which is why most febrile seizures are short and followed by normal behaviour within an hour. ^[1]

The same mechanism explains the child's temperature behaviour around the seizure: the seizure tends to occur early in the febrile illness, sometimes when the temperature is first rising and before the parents realise the child is unwell. ^[1] It also explains the difference between the two types: a short generalised discharge that terminates on its own, versus a sustained or repeated discharge that counts as a complex seizure and carries a different prognosis. ^[1]

Take the history from parents, eyewitnesses and, when old enough, the child. The aim is to reconstruct the convulsion minute by minute, identify the cause of the fever, and decide whether the event was simple or complex. ^[1]

• The convulsion. Ask about the exact words used by the parent: did the child go stiff, did the eyes roll, was there shaking of all four limbs or only one side, was one side used afterwards, how long did the shaking last, and how long until the child was back to normal. A postictal focal weakness, called Todd paralysis, means the seizure was focal and therefore complex. ^[1]
• Timing. Note the interval between the first noticeable fever and the seizure; a fever duration of less than one hour before onset is one of the risk factors for recurrence. ^[1]
• Cause of the fever. Upper respiratory symptoms, vomiting or diarrhoea, ear pain, rash, urinary symptoms, and recent immunisations. ^[1]
• Risk factors. Immunisation status for H. influenzae type b and S. pneumoniae, recent antibiotics, personal or family history of seizures or epilepsy, and any developmental or neurological abnormality. ^[1][5]
• Recovery. Whether the child was sleepy or perfectly normal afterwards, and how long that lasted.

A simple febrile seizure usually needs no further tests. The history is the diagnosis. ^[1][5]

Examine the child fully once the seizure has ended and consent has been obtained. Key tasks: assess airway, breathing and circulation; measure and record temperature; look for a focus of infection; perform a full neurological examination including level of consciousness, tone, and any focal deficit; and assess hydration and perfusion. ^[1]

Focal neurological signs, an altered level of consciousness that does not improve, or signs of meningitis or sepsis demand immediate investigation. ^[1][5] In a recovered, well child the examination is otherwise an opportunity to reassure and to exclude danger, not to create tests.

A febrile convulsion is a diagnosis of exclusion, because at this age a fever and shaking can also mean meningitis, encephalitis, or a first presentation of epilepsy. The following table separates the common mimics by the feature that distinguishes each. ^[1]

Breath-holding spells deserve specific mention. They are common between six months and five years, are not epileptic seizures, and begin with a cry and a held breath, followed by pallor or cyanosis, loss of tone and brief stiffening. Recovery is rapid and there is no postictal phase. Reassuring the parents and preventing triggers is the management; antiepileptic drugs are not used. ^[1] A first atypical episode that does not fit this pattern should not be assumed to be benign.

In a child who is now well and had a simple febrile seizure, the history and examination are sufficient. Blood tests, neuroimaging and electroencephalography are not required, and the child's family can usually be reassured and sent home. ^[1][5] The exceptions below are the ones that matter in examination questions and in emergency practice.

Meningitis is the condition most likely to be confused with a febrile seizure, and it is the dangerous one. However, a well child who had only a simple febrile seizure has no greater risk of bacterial meningitis than any other febrile child. ^[1] Retrospective and case series data show that when meningitis is the cause, the child has additional findings: reduced level of consciousness, nuchal rigidity, prolonged or focal seizure, petechial rash, or multiple seizures in a short period. ^[1]

Therefore routine lumbar puncture is not recommended for a well-appearing child with a simple febrile seizure. ^[1][5] Perform it, or consider it as an option, in these situations: ^[5]

• the child has clinical signs or symptoms of concern for meningitis, such as obtunded or comatose mental status, nuchal rigidity, prolonged focal seizure, or petechial rash;
• the child is between 6 and 12 months of age and has incomplete or unknown immunisation status for H. influenzae type b or S. pneumoniae, or immunisation status cannot be determined; ^[5]
• the child has been pretreated with antibiotics, which may blunt the presentation of bacterial meningitis;
• the child has febrile status epilepticus, that is, a prolonged febrile seizure, because acute bacterial meningitis was found in four of 24 children in one series. ^[1]

In children with complex febrile seizures the neurological examination, not the checklist alone, guides whether to do a lumbar puncture. ^[1]

Neuroimaging is unnecessary for a simple febrile seizure. ^[1][5] For a complex seizure the risk of finding an intracranial abnormality is low: in one case series of 526 children with a first complex febrile seizure, only four had clinically significant intracranial pathology, and three of those four had obvious abnormalities on examination. ^[1] Obtain imaging only when the child has abnormal or focal neurological findings, or when the seizure characteristics and examination make you suspicious of a structural lesion. ^[1]

EEG has no role in the acute management of a febrile seizure and does not predict recurrence. ^[1][5] An outpatient EEG is reserved for children who have several risk factors for epilepsy, such as developmental delay, a family history of epilepsy, or more than one defining feature of a complex febrile seizure. ^[1]

Routine blood tests are not indicated for a simple febrile seizure in a well child. ^[1][5] When the child appears unwell, electrolyte, glucose and infection investigations should follow the clinical picture, and a urine dipstick is reasonable when urinary infection is suspected. If the child has persistently abnormal mental status between or after seizures, check blood glucose and electrolytes. ^[1]

There is no scoring system for febrile seizures; the diagnosis is clinical: age six months to five years, fever, convulsion, no central nervous system infection, and no previous afebrile seizures. ^[1][6]

Any child who has a seizure lasting more than five minutes, or who does not return towards baseline afterwards, needs hospital assessment, even if the diagnosis ultimately is simple febrile seizure. ^[1]

Most febrile seizures stop on their own in under five minutes. Pre-hospital and emergency priorities are airway, breathing and circulation. ^[2]

• Protect the child from injury, but do not restrain and do not put anything in the mouth. ^[1]
• Turn the child onto the side into the recovery position once the shaking stops. ^[1]
• Time the seizure and check temperature and oxygen saturation.
• Check blood glucose, particularly if the child is drowsy, malnourished or there is any doubt about intake.
• Give oxygen if needed and keep the airway clear.
• Do not attempt to cool the child aggressively; sponge baths do not stop seizures and may cause distress. Treat the fever with a normal antipyretic dose only for comfort.

Once settled, the child can usually be managed at home if they are well, the seizure was simple, and follow-up is reliable. Hospital admission is more likely in the very young, those with abnormal examination findings, complex features, or unreliable follow-up. ^[1]

Seizures lasting more than five minutes are unlikely to stop on their own, and a benzodiazepine should be given to break them. ^[1][2] This is the one drug decision that all sources agree on.

In hospital, with intravenous access and resuscitation facilities available, intravenous lorazepam 0.1 mg per kilogram, maximum 4 mg per dose, is widely used and is as effective as diazepam, with a similar rate of respiratory depression. ^[2] Intravenous diazepam 0.2 mg per kilogram, maximum 10 mg per dose, or intravenous midazolam 0.2 mg per kilogram, maximum 10 mg per dose, are acceptable alternatives. ^[2] A 2018 Cochrane review reached the same conclusions for intravenous lorazepam and diazepam. ^[1]

When intravenous access is not available, buccal midazolam or rectal diazepam is acceptable. ^[1] NICE names buccal midazolam as the first choice in the community, with rectal diazepam as an alternative if agreed, based on previous use or if buccal midazolam is unavailable. ^[3] In younger children under three years, rectal diazepam 5 mg is often used as an initial rescue medicine before switching to buccal midazolam when the child is older. ^[2] Intranasal benzodiazepines are commonly used but the Cochrane review concluded that there is insufficient evidence to support them. ^[1]

NICE guidance is that in the community, when no individualised emergency plan is available, a benzodiazepine should be given immediately as first-line treatment for convulsive status epilepticus, with intravenous lorazepam used if intravenous access and resuscitation facilities are immediately available. ^[3] Buccal midazolam is the usual first choice in community practice in the United Kingdom, with rectal diazepam as an alternative when preferred or when buccal midazolam is not available. ^[3] If the seizure does not stop within 5 to 10 minutes of the first dose, a second dose may be given. ^[3] More than two benzodiazepine doses are not recommended, because of the risk of respiratory depression. ^{[2] [1]}

Doses vary by product and by age; always check the current product label or local formulary, and remember that all benzodiazepines can cause respiratory depression, especially when repeated or combined. ^[1][2]

Antipyretics are for comfort, not for seizure prevention. A Cochrane review found no benefit of antipyretic drugs in preventing febrile seizure recurrence. ^[1][4] Parents should still be taught to treat fever for comfort with paracetamol (acetaminophen) or ibuprofen at standard paediatric doses: paracetamol 10 mg per kilogram per dose up to four doses in 24 hours and ibuprofen 5 mg per kilogram per dose every six hours. ^[2]

One finding adds useful nuance: in a Japanese randomised trial of 423 children with febrile seizure, rectal paracetamol 10 mg per kilogram every six hours for 24 hours reduced short-term recurrence to 9.1 percent, compared with 23.5 percent without antipyretics, a number needed to treat of 7. ^[1] This is short-term prevention within the same fever, not prevention of the next febrile illness, and it does not make routine antipyretics seizure-preventing medication.

Given the benign natural course of simple febrile seizures, routine continuous or intermittent antiepileptic therapy is not recommended after a first episode, because adverse effects occur in up to 30 percent of children treated in this way. ^[1][4] Intermittent diazepam at the onset of fever and continuous phenobarbital do reduce recurrence in randomised trials, but the balance of benefit against sedation, behavioural effects and monitoring burden is unfavourable for routine use. ^[1][4]

Prophylaxis is genuinely controversial only in a small subgroup: a child who has had an extremely prolonged or frequently recurring febrile seizure, or one with marked parental anxiety and documented high recurrence risk. In that setting oral or rectal diazepam at the onset of fever may be considered as a short course, with the family taught exactly when to give it. ^[1] Such decisions belong to a paediatric neurologist and the family together.

Zinc supplementation has been studied and has not been shown to prevent febrile seizures. ^[1]

This is the management for most families, and the evidence supports prolonged attention to it. Advise parents that: ^[1]

• the seizure itself is not brain damage; most children are entirely normal afterwards and a simple febrile seizure does not reduce intelligence, school performance or behaviour;
• the risk of a further febrile seizure is about 33 percent after one, and it depends mainly on how young the child is at the first attack and on how high the temperature was; use the recurrence table below to give an honest individual estimate; ^[1]
• there is no difference in recurrence risk between an initial simple and an initial complex febrile seizure;
• children with a simple febrile seizure have no increase in long-term mortality, whereas complex febrile seizures carry a small increase over the next two years, mainly reflecting underlying neurological disease. ^[1]

Practical seizure care to teach: protect the child from hard objects, do not restrain, do not put anything in the mouth, time the event, and place the child in the recovery position once it stops; encourage normal activity as soon as the child feels well. The child may be drowsy and should be allowed to sleep. Parents should call emergency services without waiting if the seizure lasts more than five minutes, if it is focal, if more than one occurs, or if breathing is not normal afterwards. ^[1]

Risk factors: aged under 18 months at the first seizure; fever duration of less than one hour before the seizure; a first-degree relative with a history of febrile seizure; and a peak temperature below 40 degrees Celsius (104 degrees Fahrenheit). ^[1]

• Status epilepticus. Some first febrile seizures become prolonged (febrile status epilepticus). Because acute bacterial meningitis was found in 4 of 24 children with febrile status epilepticus in one series, a prolonged seizure always raises suspicion of serious infection. ^[1]
• Recurrence at a later time, which is common but not dangerous in itself; see the prognosis below.
• Postictal Todd paralysis after a complex seizure, which implies a focal seizure.
• Complications of evaluation or treatment: unnecessary lumbar punctures, sedation and respiratory depression from benzodiazepines, and the consequences of withholding immunisations.
• Febrile seizures are not a surgical disease.

The outlook is excellent for the great majority. Children with simple febrile seizures have no increase in long-term mortality compared with the general population and no difference in academic progress, intelligence or behaviour at ten years. ^[1] Children with complex febrile seizures have a slightly increased mortality over the next two years (adjusted mortality rate ratio 1.99), but this reflects more advanced neurological disease and subsequent epilepsy rather than the seizure itself. ^[1]

Children who have had a febrile seizure are about five times more likely than other children to develop an unprovoked seizure later. ^[1] The absolute risks are what parents need:

• about 2.4 percent in children whose febrile seizures were all simple; ^[1]
• 6 to 8 percent in children with complex seizures; ^[1]
• 17 to 22 percent if the child had any two complex features; ^[1]
• 49 percent if all three complex features were present. ^[1]

The same risk factors appear in research cohorts: onset after three years of age, a complex febrile seizure, family history of epilepsy, fever lasting less than one hour before onset, and an existing neurodevelopmental abnormality. ^[1] Complex febrile seizures, especially prolonged ones, are the main bridge between febrile seizure and epilepsy, and that is why they deserve the closer evaluation described above. ^[1]

Developmental delay and a family history of epilepsy are the strongest markers for follow-up: offer these children follow-up with paediatric neurology, and discuss the epilepsy risk openly without alarm. ^[1]

There is no primary prevention of febrile seizures, and no screening test identifies the children who will have them. Prevention therefore means preventing the infections that provoke high fever. ^[1]

Every child should receive all routine immunisations on schedule. The measles-mumps-rubella vaccine increases febrile-seizure risk by a small early-life amount; the risk from measles itself, and from waiting, is far larger. ^[1] Antipyretics do not need to be given after vaccination and may blunt antibody responses. ^[1]

A child who has had one febrile seizure does not need an EEG, brain scan or blood test to predict the next one. ^[1][5]

• Infants aged 6 to 12 months deserve careful assessment of immunisation status. Where that status is unknown, incomplete or unverified, and the child presents with a first febrile seizure, a lumbar puncture is an option because the clinical signs of meningitis are less reliable at that age. ^[5]
• Children with complex features should be evaluated by their neurological status and may need outpatient EEG; cross-reference this with the investigations above.
• Children with neurodevelopmental delay have both a higher risk of epilepsy and less reliable examination; involve paediatric neurology early.
• Adolescents and adults do not have febrile seizures in this sense; an adult with a convulsion and fever needs a full work-up for meningitis, encephalitis or epilepsy.
• Pregnancy is not a topic for this condition, which is confined to early childhood.

The same principles apply where investigations are scarce, and they can be followed without a laboratory. ^[1][5]

• Decide clinically. Assess airway and circulation, look for a focus of infection, and check whether the child is conscious between and after seizures. Meningitis is diagnosed by clinical signs, not by a scan.
• Reserve lumbar puncture for clear indications - altered consciousness, meningeal signs, prolonged or focal seizure, a petechial rash, multiple seizures, febrile status epilepticus, or the uncertainly immunised infant. Do not do lumbar puncture routinely in a recovered child. ^[1][5]
• Use the test you have. Urine dipstick, malaria microscopy or rapid diagnostic tests, and careful measurement of glucose cost little and change management.
• Antipyretics are usually available and should be used for comfort at standard doses. ^[2]
• Rescue medication. Rectal diazepam is the practical community rescue drug where buccal midazolam is unavailable, and diazepam tablets may be crushed or used rectally in some settings. Train the parents and the nearest health worker before discharge; nothing else prevents status epilepticus if the rescue drug is late.
• Refer early if the child has a complex febrile seizure, focal signs, an abnormal developmental examination, or seizures that are prolonged or repeated, or if the family cannot return easily. Rectal diazepam and clear transport instructions are the bridge between rural clinic and hospital.
• Health education explaining that a short febrile seizure is common and usually harmless does as much for families as any medicine.

• A febrile seizure occurs in a child aged six months to five years, with fever of at least 38 degrees Celsius and no central nervous system infection; it is the commonest convulsive event of childhood, affecting 2 to 5 percent of children. ^[6]
• Simple seizures are generalised, last under 15 minutes and occur once per 24 hours; any more complex feature makes the seizure complex and changes the evaluation and prognosis. ^[1]
• The cause is a fever-lowered seizure threshold in a developing brain; it is not brain infection, and the event is usually self-limiting. ^[1]
• Meningitis must be actively excluded by history and examination, but a well child with a simple febrile seizure does not need a routine lumbar puncture, blood test, EEG or brain scan. ^[1][5]
• Lumbar puncture is indicated or strongly considered for abnormal examination, febrile status epilepticus, an uncertainly immunised infant aged 6 to 12 months, and pretreatment with antibiotics. ^[1][5]
• Complex seizures need neurological examination to guide imaging and lumbar puncture; EEG is outpatient and only when risk factors for epilepsy are present. ^[1]
• Treat a seizure lasting more than five minutes with a benzodiazepine: intravenous lorazepam 0.1 mg per kilogram, or diazepam 0.2 mg per kilogram, or midazolam 0.2 mg per kilogram in hospital, and buccal or rectal benzodiazepine in the community. ^[2][3]
• Give no more than two benzodiazepine doses, because of respiratory depression. ^[2]
• Antipyretics relieve discomfort; they do not prevent recurrent febrile seizures, though rectal paracetamol reduced short-term recurrence in one trial. ^[1]
• Continuous or intermittent antiepileptic drugs are not recommended after a first febrile seizure because of adverse effects in up to 30 percent of children, despite small reductions in recurrence. ^[1][4]
• The average recurrence risk is about 33 percent over two years; it ranges from 14 percent with no risk factors to 75 percent with all four. ^[1]
• Children with simple febrile seizures have normal long-term cognition, academic progress and mortality; complex seizures carry a small excess mortality mainly from underlying disease. ^[1]
• Lifetime risk of unprovoked seizure is about 2.4 percent after simple seizures and 6 to 8 percent after complex, rising to about 49 percent when all three complex features occur. ^[1]
• Immunisation should proceed on schedule; the benefits of vaccination far outweigh the small increase in febrile seizure risk, and antipyretics are not given routinely after vaccination. ^[1]
• Most families need reassurance, first-aid instruction, a clear recurrence estimate and a written emergency plan, not drugs. ^[1]

• Fever in the infant and child (assessment and red flags)
• Status epilepticus in children
• Childhood meningitis and encephalitis
• Epilepsy: classification and first approach
• Immunisation schedule and febrile illnesses
• Breath-holding spells and other paroxysmal events in childhood

In practice this topic links naturally to paediatric neurology topics that may be added later; check the MedGrasp topic registry before converting the plain-text mentions above into formal links.