Febrile Seizures

A febrile seizure, is a seizure associated with an increased body temperature but without any intracranial infection.

Febrile seizures affect 2–7% of children and are more common in boys than girls.

They most commonly occur in children between the ages of 6 months and 5 years with a higher incidence around 18 month of age.

Most seizures last less than five minutes, and the child usually recovers quickly.

Children with the onset of febrile seizures before the age of 1 year have deficits in learning, consolidation and delayed recognition.

Most febrile seizures do not adversely affect global measures of intelligence in children older than 1 year of age.

About 1 in every 25 children will have at least one febrile seizure, and about one third of these children will have more.

Increased risk after administration of whole-cell pertussis vaccine.

Febrile seizures can occur in any ethnic group, although there have been higher rates in Guamanians (14%), Japanese (6–9%) and Indians (5–10%).

There are two types of febrile seizures: simple and complex.

Simple febrile seizures involve an otherwise healthy child with a single, one episode of generalized seizure lasting less than 15 minutes.

Complex febrile seizures have one of more of the following: focal symptoms such as jerking of only one side of the body, duration greater than 15 minutes, or two or more seizures within 24 hours.

About 60–70% are classified as simple febrile seizures and 30–40% complex.

Febrile seizures are triggered by fever, usually due to a viral infection.

In children, illnesses that often cause a fever include middle ear infections and viral upper respiratory infections.

Other infections associated with febrile seizures include Shigellosis, Salmonellosis, and particularly Roseola (HHV6).

There is a small chance of a febrile seizure after certain vaccines.

The risk is only increased for about 10 days after receiving one of the implicated vaccines during the time when the child is likely to develop a fever as a natural immune response.

Implicated vaccines include: MMRV (measles, mumps, rubella, varicella) combined diphtheria / tetanus / acellular pertussis / polio / Haemophilus influenzae Type B

diphtheria-tetanus-whole-cell pertussis some versions of the pneumococcal vaccine, some types of inactivated influenza vaccine.

Febrile seizures are thought to involve genetics, environmental factors, brain immaturity, and inflammatory mediators, such as proinflammatory cytokine IL-1β.

The rapid rise and decrease of the body temperature is not the main mechanism for febrile seizure occurrence. 

The diagnosis must confirm that there is not an infection of the brain, and there have not been prior seizures without a fever.

Blood tests, imaging of the brain, or an electroencephalogram (EEG) are typically not needed.

Examination to determine the source of the fever is required, and in otherwise healthy-looking children, a lumbar puncture is not necessarily required.

After a single febrile seizure there is an approximately 35% chance of having another one during childhood.

Anti-seizure medications nor anti-fever medications are recommended in an effort to prevent further febrile seizures.

Efforts to rapidly cool the child’s body during a seizure are not recommended.

The long-term outcome of children with febrile seizures is excellent, with similar academic achievements to other children.

Children with febrile seizures have a slightly increased risk of epilepsy at 2–3% compared to the general population risk of about 1%.

With febrile seizures,  temperature is greater than 38 °C (100 °F), although most have a fever of 39 °C (102 °F).

Most febrile seizures occur during the first 24 hours of developing a fever.

Typical seizure activity include: loss of consciousness, opened upturned eyes, irregular breathing, increased secretions or foaming at the mouth, and the child may look pale or cyanotic, sometimes the body stiffens with rhythmic jerk of arms and legs, and incontinence and vomiting may occur.

After the seizure the child may enter a post ictal state.

The distinction between simple and complex is based on the risk of subsequent epilepsy.

Simple febrile seizures have a very low risk (~2%) of later epilepsy without fever).

The risk of epilepsy following complex febrile seizures depends on the number of  features with each factor adding about a 5% risk.

A child with all three factors have a risk of subsequent epilepsy of about 15%. 

Febrile status epilepticus (FSE) implies that the seizure lasts for longer than 30 minutes.

It occurs in up to 5% of febrile seizure cases and has some special long-term concerns.

There is evidence that many children with febrile seizures have a genetic predisposition to have febrile seizures.

Identical twins are much more likely to also have a febrile seizure than if the twin is non-identical.

First degree relatives of a child with febrile seizures have a risk of 10–15% of having a febrile seizure compared with the general risk in the population of only 3–4%.

At least 20 chromosomal specific mutated genes coming from these have been identified: SCNA1, SCN1B, SNCA9A, GPR98, GABRG2.

The exact pattern of inheritance of febrile seizure susceptibility genes is usually unclear.

The mode of inheritance is autosomal dominant – Dravet syndrome and genetic epilepsy with febrile seizures plus +.

Dravet syndrome is a epilepsy syndrome caused by mutations in the gene SCN1A, usually with prolonged, often focal, febrile seizures in the first year of life followed by severe epilepsy. 

Dravet syndrome is usually not inherited. 

The syndrome of GEFS+ (genetic epilepsy with febrile seizures plus) is an autosomal dominant condition with mutations in the SCN1A gene.

The syndrome of GEFS+ affects  family members who have febrile seizures that may be followed by later development if a variety of types of epilepsy.

Risk factors for an initial febrile seizure include a family history of febrile seizures, delay in going home after birth, possible slow development and possibly attendance at day care with increased  the risk of illnesses.

Children with all of these factors have a risk for a first febrile seizure of about 30%.

Febrile seizures are more likely to occur in children with developmental delay, and lower socio-economic status due to a higher rate of infectious illness.

Studies in developing countries have shown an association between febrile seizures and iron deficiency anemia, and lowered zinc levels.

Mechanism of febrile seizures is unknown.

It is suggested that multi-factorial processes involving genetic and environmental factors accounts for febrile seizures.

It is proposed that inflammatory mediators, particularly cytokines (including IL-1β) play a role in febrile seizures: children with febrile seizures have different amounts of some cytokines compared with children without febrile seizures.

Evidence suggests that febrile seizures are an age-related phenomenon due to increased excitability of the brain during normal development.


If the child presents with seizure at the time of assessment, emergency treatment to stop the seizure should be initiated, usually with intravenous diazepam, lorazepam or midazolam.

If intravenous access is difficult then rectal diazepam or intranasal midazolam or buccal midazolam may be effective.

The diagnosis of a febrile seizure can be confirmed by detailed history including the value of highest temperature recorded, timing of seizure and fever, seizure characteristics, time to return to baseline, vaccination history, illness exposures, and family history.

A physical exam to find the source of the fever, to exclude meningitis and assess neurological status is required.

Mimics of febrile seizures: shivering, febrile delirium, febrile myoclonus, breath holding spells, convulsive syncope and benign convulsions with mild gastroenteritis.

Meningitis and encephalitis must be excluded which may be challenging since small children may not show the typical signs of meningitis such as stiff neck.

After a first febrile seizure, the overall risk of another febrile seizure during another febrile illness is 30–40%, and this typically occurs within the next year.

The most consistent factor that increases the risk of recurrence is age less than one year.

Factors that increase the risk of recurrence are a family history of febrile seizures, a low temperature (below 39 °C (102 °F)) at the time of the first seizure, and a short duration of fever before the first febrile seizure.

Children with none of these factors have a recurrence risk of about 20% and those will all of the factors have a risk of about 60–70%.

Daily phenytoin, valproate, pyridoxine and zinc sulfate do not prevent further febrile seizures.

Daily phenobarbital does reduce the risk of recurrence but about 30% of children treated in this way have significant side effects and it is not recommended.

With oral diazepam at the time of fever, 14 children need to be treated to prevent one febrile seizure.

No evidence to support the use of fever reducing medications of acetaminophen, ibuprofen or diclofenac at the time of fever to prevent a recurrent febrile seizure.

Tepid sponging plus antipyretic medications has a modest effect on reducing the temperature of febrile children although the value of this treatment to prevent febrile seizures has not been documented.

Recommendations are made for febrile seizures:

If the seizure lasts longer than 5 minutes, call an ambulance.

Only if previously prescribed, rectal diazepam or intranasal midazolam may be used.

The child should be taken immediately to the nearest medical facility for further diagnosis and treatment.

Place the child on a protected surface such as the floor or ground to prevent accidental injury.

Do not restrain or hold a child during a convulsion.

Position the child on their side or stomach to prevent choking. 

Remove any objects from the child’s mouth. 

Seek immediate medical attention if this is the child’s first febrile seizure, 

This is especially urgent if the child shows symptoms of a stiff neck, extreme lethargy, or abundant vomiting, signs of meningitis.

A single seizure lasting greater than 5 minutes, cyanosis, or two consecutive seizures lasting greater than 5 minutes without recovery between the seizures are concerning for the development of febrile status epilepticus.

Status epilepticus may damage the brain and should be stopped promptly with intravenous lorazepam, rectal or intranasal diazepam, or intranasal midazolam.

Most children with febrile status epilepticus recover completely with normal intelligence.

The  long-term outcomes for febrile seizures are generally good with little risk of neurological problems or epilepsy.

With one febrile seizure there is an approximately 30–40% chance of having another one in the next two years, with the risk being greater in those who are younger.

Simple febrile seizures do not tend to recur frequently,  and are associated with a slight increase in later epilepsy of about 2–3%, compared with the general public without febrile seizures (1%).

Children with a first febrile convulsion are more likely to have a recurrent febrile seizure if they were young at their first seizure, have a family history in first-degree relatives, have a short time between the onset of fever and the seizure, had a low degree of fever before their seizure, or have a history of abnormal neurological signs or developmental delay.

Children with a first prolonged febrile seizure are not at increased risk of a recurrent febrile seizure.

The prognosis after a complex febrile seizure is usually excellent, but 

About 10–15% will eventually develop epilepsy but 85–90% will not.

A single study suggested that, compared with the normal population, children with complex febrile seizures had a slightly increased risk of death in the two years after their first febrile seizure: Once two years had passed since their first febrile seizure, children with complex febrile seizures no longer had an increased risk of death.

About 5% of children with very long febrile seizure later develop hippocampal sclerosis.

Nearly all children with febrile seizures have a good long term prognosis.

Febrile seizures often recur, but ater epilepsy is uncommon. 

Even prolonged febrile seizures typically do not have sequelae.


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