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Febrile Seizures

by Margaret C. McBride, MD

Febrile seizures are seizures triggered by a fever.

Febrile seizures occur in about 2 to 5% of children younger than 6 years but most often occur in children aged 6 months to 3 years. A seizure that occurs in a child who has a fever and is 6 years old or older is not considered a febrile seizure. Febrile seizures may run in families. Most febrile seizures last much less than 15 minutes, and about two thirds of children who have a febrile seizure never have another one.

Febrile seizures may be simple or complex.

  • Simple: The entire body shakes (called a generalized seizure) for less than 15 minutes. Over 90% of febrile seizures are simple.

  • Complex: The entire body shakes for more than 15 minutes (constantly or with pauses), only one side of the body shakes (called a partial seizure), or seizures occur at least twice within 24 hours. Children who have complex febrile seizures are slightly more likely to develop a seizure disorder later during childhood.

Febrile seizures usually result from the fever itself. Most often, the fever is caused by an otherwise minor infection such as a viral respiratory infection or an ear infection. In such cases, the infection and the seizure are harmless. However, sometimes life-threatening brain infections, such as meningitis (see Acute Bacterial Meningitis) or encephalitis (see Encephalitis), also cause seizures (as well as fever). Because parents cannot tell whether children have such a brain infection, children who have a fever and who have a seizure for the first time or are very sick should be taken to the emergency department for evaluation. Doctors examine the children and, depending on what they find, sometimes do tests to check for these and other serious disorders that can cause seizures. These tests may include a spinal tap (lumbar puncture) with analysis of the fluid around the spinal cord (cerebrospinal fluid) and blood tests to measure levels of sugar (glucose), calcium, magnesium, sodium, or other substances. If the seizure affected only one side of the body, imaging of the brain with computed tomography (CT) or magnetic resonance imaging (MRI) may be done.

Did You Know...

  • Most children who have a febrile seizure have only one.

Prognosis

About one third of children have additional febrile seizures, but usually only a few. Children are more likely to have additional seizures if they were under 1 year old when they had the first febrile seizure or if they have close relatives who have had febrile seizures.

Children who have had a simple febrile seizure have a slightly increased risk of developing a seizure disorder that does not involve a fever (nonfebrile seizures, or epilepsy). If children have had a complex febrile seizure or have additional risk factors (such as developmental delay or a family history of seizures), the risk is higher (up to 10%). In some children, having a very long febrile seizure results in changes in the brain (identified by MRI) that lead to nonfebrile seizures later. In such cases, doctors are not sure whether having a long febrile seizure by itself makes nonfebrile seizures more likely or whether some underlying factors make the children more likely to have both the long febrile seizure and the later nonfebrile seizures.

Febrile seizures that do not last a long time are not thought to cause epilepsy or other neurologic abnormalities. However, a febrile seizure is sometimes the first sign of a previously unrecognized neurologic disorder. Sometimes doctors can look back and see signs of that disorder in the child's past history. Sometimes other signs of the disorder do not appear until later. In either case, the febrile seizure is not thought to cause the abnormalities.

Treatment

Usually, seizures last less than 15 minutes, and no treatment is given other than drugs to reduce the fever. If a seizure lasts 15 minutes or more (called status epilepticus), doctors give drugs to end the seizure (see Neurologic Disorders in Children:Emergency treatment).

Drugs to prevent additional seizures (anticonvulsants—see Table: Using Drugs to Treat Seizures in Children) are usually not given to children who have had only a few simple febrile seizures. However, children who have had many febrile seizures or seizures lasting a long time may be given such drugs for a period of time. If children have had a long febrile seizure, doctors may prescribe diazepam gel to be applied to the rectum if a subsequent seizure lasts more than 5 minutes.

If children have had a febrile seizure, parents should watch for and treat high fevers, which can trigger a seizure.

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