Febrile seizures are diagnosed in children < 6 yr with body temperature > 38°C and no previous afebrile seizures when no cause can be identified. 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 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, and if they occur in a series, total duration is < 30 min.
• Complex febrile seizures last > 15 min and have focal features or postictal paresis, or occur in a series with a total duration of > 30 min.

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 may 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.

Diagnosis

• Exclusion of other causes

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 such children have already shown a tendency to have seizures.

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
• 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 CT or MRI if examination detects focal features or if there are signs of increased intracranial pressure
• Consideration of EEG if febrile seizures are complex or recurrent

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

Overall recurrence rate 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 experiencing febrile seizures is about 2 to 5%, unless children have additional risk factors (eg, complex febrile seizures, family history of seizures, developmental delay), which increase risk up to 10%.

Treatment

• Supportive therapy if seizures last < 15 min
• Drugs and sometimes intubation if seizures last ≥ 15 min

Treatment is supportive if seizures last < 15 min.

Seizures lasting ≥ 15 min 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 2 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.

Maintenance drug therapy to prevent recurrent febrile seizures or development of afebrile seizures is usually not indicated unless multiple or prolonged episodes have occurred.

Last full review/revision May 2009 by Margaret C. McBride, MD