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Febrile Seizures

by Margaret C. McBride, MD

Febrile seizures are diagnosed in children < 6 yr with body temperature > 38°C and no previous afebrile seizures when no cause can be identified and no underlying developmental or neurologic problem exists. Diagnosis is clinical after exclusion of other causes. Treatment of seizures lasting < 15 min is supportive. Seizures lasting 15 min 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 yr; most occur at age 6 to 36 mo. Febrile seizures may be simple or complex:

  • Simple febrile seizures last < 15 min and have no focal features.

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

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 h 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 features (eg, diminished movement on one side) during this period, it is important to immediately evaluate for an underlying CNS disorder.

Febrile status epilepticus is continuous or intermittent seizures that last ≥ 20 min without neurologic recovery between them.

Diagnosis

  • Exclusion of other causes clinically or sometimes by testing

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:

  • CSF analysis to rule out meningitis and encephalitis if children are < 6 mo, have meningeal signs or signs of CNS depression, or have seizures after several days of febrile illness and consideration of CSF analysis if children are not fully immunized or are taking antibiotics

  • Serum glucose, Na, Ca, Mg, and P and liver and kidney function tests to rule out metabolic disorders 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

  • Cranial MRI if neurologic examination detects focal abnormalities or if focal features occur during the seizure or postictal period

  • EEG if febrile seizures have focal features or are recurrent

  • A diagnostic evaluation based on the underlying disorder 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; 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 yr 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 with an unrecognized neurologic disorder, a febrile seizure may be the first manifestation; signs of the disorder may be identified retrospectively or not appear until later. In either case, the febrile seizure is not thought to be causal.

Complex febrile seizures such as focal seizures or 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 < 15 min

  • Drugs and sometimes intubation if seizures last 15 min

All children require antipyretic therapy (see Fever in Infants and Children : Treatment); lowering temperature can help prevent another febrile seizure during the immediate illness and makes it easier to stop febrile status epilepticus.

Treatment is supportive if seizures last < 15 min.

Seizures lasting 15 min 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 min repeated q 5 to 10 min for up to 3 doses). Fosphenytoin 15 to 20 mg PE (phenytoin equivalents)/kg may be given over 15 min if the seizure persists. In children up to 5 yr, diazepam rectal gel 0.5 mg/kg may be given once and repeated in 4 to 12 h if lorazepam cannot be given IV. Phenobarbital, valproate, or levetiracetam can also be used to treat a persistent seizure.

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 this treatment does not necessarily prevent febrile seizures from recurring. Maintenance anticonvulsant drug therapy to prevent recurrent febrile seizures or development of afebrile seizures is usually not indicated unless multiple or prolonged episodes have occurred. As an alternative to maintenance anticonvulsant therapy in such children, some clinicians prescribe oral diazepam to be given by parents at the onset of a febrile illness and/or rectal diazepam to be given for a prolonged febrile seizure.

Key Points

  • Febrile seizures are seizures that occur in neurologically normal children < 6 yr with a temperature of > 38°C and no previous afebrile seizures and that have no identifiable cause.

  • Simple febrile seizures last < 15 min and have no focal features.

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

  • 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 15 min require drug treatment (eg, lorazepam 0.05 to 0.1 mg/kg IV over 2 to 5 min repeated q 5 to 10 min for up to 3 doses).

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

Drugs Mentioned In This Article

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

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