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Febrile Seizures

By

M. Cristina Victorio

, MD, Northeast Ohio Medical University

Last full review/revision Oct 2019| Content last modified Oct 2019
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Febrile seizures are diagnosed in children 6 months to 5 years of age who have fever > 38° C that is not caused by a central nervous system infection and who have had no previous afebrile seizures. Diagnosis is clinical after exclusion of other causes. Treatment of seizures lasting < 5 minutes is supportive. Seizures lasting 5 minutes are treated with IV lorazepam, rectal diazepam, or intranasal midazolam and, if persistent, IV fosphenytoin, phenobarbital, valproate, or levetiracetam. Maintenance drug therapy is usually not indicated.

Febrile seizures occur in about 2 to 5% of children 6 months to 5 years of age, and most occur between 12 months and 18 months of age. Febrile seizures may be simple or complex:

  • Simple febrile seizures last < 15 minutes, have no focal features, and do not recur within a 24-hour period.

  • Complex febrile seizures last ≥ 15 minutes continuously or with pauses, or have focal features, or recur within 24 hours.

Most (> 90%) febrile seizures are simple.

Febrile seizures occur during bacterial or viral infections. They sometimes occur after certain vaccinations such as measles, mumps, and rubella. Genetic and familial factors appear to increase susceptibility to febrile seizures. Monozygotic twins have a much higher concordance rate than dizygotic twins. Several genes associated with febrile seizures have been identified.

Symptoms and Signs

Often, febrile seizures occur during the initial rapid rise in body temperature, and most develop within 24 hours of fever onset. Typically, seizures are generalized; most are clonic, but some manifest as periods of atonic or tonic posturing.

A postictal period of a few minutes is common but may last as long as a few hours. If the postictal period is longer than an hour or if children have focal findings (eg, diminished movement on one side) during this period, it is important to immediately evaluate for an underlying acute central nervous system (CNS) disorder.

Febrile status epilepticus is continuous or intermittent seizures that last ≥ 30 minutes without neurologic recovery between them. Children with status epilepticus are at risk of brain damage (1).

Symptoms and signs reference

Diagnosis

  • Exclusion of other causes clinically or sometimes by testing

(See also the American Academy of Pediatrics Subcommittee on Febrile Seizures' guidelines for the neurodiagnostic evaluation of the child with a simple febrile seizure.)

Seizures are diagnosed as febrile after exclusion of other causes. A fever may trigger seizures in children with previous afebrile seizures; such events are not termed febrile seizures because these children have already shown a tendency to have seizures.

Routine testing is not required for simple febrile seizures other than to look for the source of the fever, but if children have complex seizures, neurologic deficits, or signs of a serious underlying disorder (eg, meningitis, metabolic disorders), testing should be done.

Tests to exclude other disorders are determined clinically:

  • Cerebrospinal fluid (CSF) analysis is done to rule out meningitis and encephalitis in younger infants, in those with meningeal signs or signs of CNS depression, or in those who have seizures after several days of febrile illness. CSF analysis must also be considered if children are not fully immunized or are taking antibiotics.

  • Serum glucose, sodium, calcium, magnesium, and phosphorus and liver and kidney function tests are done to rule out metabolic disorders especially if the history includes recent vomiting, diarrhea, or impaired fluid intake; if there are signs of dehydration or edema; or if a complex febrile seizure occurs.

  • Brain MRI is done if neurologic examination detects focal abnormalities or if focal features occur during the seizure or postictal period.

  • Electroencephalography (EEG) is done if febrile seizures have focal features or are recurrent.

  • A diagnostic evaluation based on the underlying disorder is done if children have an already identified developmental or neurologic disorder (usually, the term febrile seizure is not used in such cases).

EEG typically does not identify specific abnormalities or help predict recurrent seizures, and it is not recommended after an initial simple febrile seizure in children with a normal neurologic examination.

Prognosis

Recurrence and subsequent epilepsy

Overall recurrence rate of febrile seizures is about 35%. Risk of recurrence is higher if children are < 1 year of age when the initial seizure occurs or have 1st-degree relatives who have had febrile seizures. Risk of developing an afebrile seizure disorder after having ≥ 1 simple febrile seizures is about 2 to 5%—slightly higher than the baseline risk of developing epilepsy (about 2%).

Most of the increased risk occurs in children who have additional risk factors (eg, complex febrile seizures, family history of seizures, developmental delay); in these children, risk is increased up to 10%. It is unclear whether having a febrile seizure can itself permanently lower the seizure threshold or whether some underlying factors predispose children to both febrile and nonfebrile seizures.

Neurologic sequelae

Simple febrile seizures themselves are not thought to cause neurologic abnormalities. However, in some children, a febrile seizure may be the first manifestation of an underlying seizure disorder or unrecognized neurologic disorder. The signs of the disorder may be identified retrospectively or may not appear until later. In either case, the febrile seizure is not thought to be causal.

Prolonged febrile status epilepticus may be associated with damage to vulnerable parts of the brain such as the hippocampus.

Treatment

  • Antipyretic therapy

  • Supportive therapy if seizures last < 5 minutes

  • Antiseizure drugs and sometimes intubation if seizures last 5 minutes

All children require antipyretic therapy because lowering the temperature can help prevent another febrile seizure during the immediate illness and makes it easier to stop febrile status epilepticus.

Treatment of febrile seizures is supportive if seizures last < 5 minutes.

Seizures lasting 5 minutes may require drugs to end them, with careful monitoring of circulatory and respiratory status. Intubation may be necessary if response is not immediate and the seizure persists.

Drug therapy is usually IV, with a short-acting benzodiazepine (eg, lorazepam 0.05 to 0.1 mg/kg IV over 2 to 5 minutes repeated every 5 to 10 minutes for up to 3 doses). Fosphenytoin 15 to 20 mg PE (phenytoin equivalents)/kg IV may be given over 15 to 30 minutes if the seizure persists. In children up to 5 years of age, diazepam rectal gel 0.5 mg/kg may be given once and repeated in 4 to 12 hours if lorazepam cannot be given IV. Phenobarbital, valproate, or levetiracetam can also be used to treat a persistent seizure.

(See also new guidelines for the management of febrile seizures in Japan.)

Prevention

Parents of a child who has had a febrile seizure should be advised to carefully monitor their child's temperature during illnesses and to give antipyretics if temperature is elevated (even though controlled studies have not shown that this treatment prevents febrile seizures from recurring).

Maintenance antiseizure drug therapy to prevent recurrent febrile seizures or development of afebrile seizures is usually not indicated unless multiple or prolonged episodes have occurred. Some clinicians prescribe rectal diazepam to be given by the parents at home for a prolonged febrile seizure.

Key Points

  • Febrile seizures are seizures that occur in neurologically normal children 6 months to 5 years of age with fever > 38° C that is not caused by a central nervous system infection and who have no previous afebrile seizures.

  • Simple febrile seizures last < 15 minutes, have no focal features, and do not recur within a 24-hour period.

  • Complex febrile seizures last > 15 minutes continuously or with pauses, or have focal features, or recur within 24 hours.

  • Routine testing is not required, but if children have complex seizures, neurologic deficits, or signs of a serious underlying disorder (eg, meningitis, metabolic disorders), testing should be done.

  • Seizures lasting 5 minutes require drug treatment (eg, lorazepam 0.05 to 0.1 mg/kg IV over 2 to 5 minutes repeated every 5 to 10 minutes for up to 3 doses).

  • Risk of developing an afebrile seizure disorder after having a simple febrile seizure is about 2 to 5%.

  • Giving an antipyretic at the beginning of a febrile illness has not been shown to prevent a febrile seizure.

More Information

  • American Academy of Pediatrics Subcommittee on Febrile Seizures' guidelines for the neurodiagnostic evaluation of the child with a simple febrile seizure

Drugs Mentioned In This Article

Drug Name Select Trade
KEPPRA
No US brand name
CEREBYX
DILANTIN
ATIVAN
VALIUM
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