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Febrile Seizures

By

M. Cristina Victorio

, MD, Northeast Ohio Medical University

Last full review/revision Mar 2020| Content last modified Mar 2020
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Febrile seizures are seizures triggered by a fever of at least 100.4° F (about 38° C).

  • Most febrile seizures are harmless and caused by fever from a minor infection.

  • Less often, a febrile seizure is the first sign of a previously unrecognized neurologic disorder.

  • Doctors sometimes do blood tests and a spinal tap to check for serious disorders that can cause seizures.

  • Children generally need drugs to end the seizure only if it lasts 5 minutes or more to minimize the risk of a long-lasting seizure or status epilepticus.

  • Most children do not need to take drugs to prevent seizures.

A seizure is an abnormal, unregulated electrical discharge of nerve cells in the brain or part of the brain. This abnormal electrical discharge can cause

  • Convulsions

  • Involuntary movements

  • Altered awareness

  • Abnormal sensations

Convulsions are violent, involuntary, jerking and stiffening of muscles in a large part of the body.

Febrile seizures occur in about 2 to 5% of children 6 months to 5 years of age but most often occur in children between 12 months and 18 months of age. A seizure that occurs in a child who has a fever and is 6 years old or older is not considered a febrile seizure. (See also Seizures in Children.)

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.

Did You Know...

  • Most 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 and children usually lose consciousness. Over 90% of febrile seizures are simple. This type of febrile seizure does not occur more than once in a 24-hour period.

  • Complex: The entire body shakes for 15 minutes or more (constantly or with pauses), or only one side or one part of the body shakes (called a partial or focal 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.

After the febrile seizure, children often appear confused or not themselves for a few minutes. The period of confusion (postictal period) sometimes lasts up to a few hours.

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. An important part of the definition of febrile seizures is that the fever and seizure are not caused by a brain infection such as meningitis or encephalitis.

Febrile status epilepticus

Status epilepticus refers to a single long-lasting seizure, or several shorter seizures that occur without the child regaining consciousness between seizures. Febrile seizures that last more than about 30 minutes are considered febrile status epilepticus. Children with status epilepticus are at risk of brain and other organ damage, as well as breathing failure, if not treated promptly.

Diagnosis

  • A doctor's evaluation

  • Sometimes a spinal tap, blood tests, or brain imaging

Because parents cannot tell whether children have 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 immediately for evaluation.

Doctors examine the children and, depending on what they find, sometimes do tests to check for serious disorders that can cause seizures. These tests may include

  • A spinal tap (lumbar puncture) with analysis of fluid from around the spinal cord (cerebrospinal fluid) to check for meningitis and encephalitis

  • Blood tests to measure levels of sugar (glucose), calcium, magnesium, sodium, or other substances to check for metabolic disorders

  • Sometimes, imaging of the brain with magnetic resonance imaging (MRI) or computed tomography (CT) (if MRI is not available) may be done.

  • Electroencephalography (EEG), which is a test that checks for abnormal electrical activity in the brain, may be done for children who have certain symptoms or who have repeat seizures.

Prognosis

About one third of children have additional febrile seizures, but usually only a few seizures. 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 (about 2%) 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 some 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.

Simple febrile seizures 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 or seizure 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

  • Drugs to reduce the fever

  • Drugs to end the seizure if it lasts 5 minutes or more

Usually, febrile seizures last less than 5 minutes, and no treatment is given other than drugs to reduce the fever.

Doctors usually give drugs to end a febrile seizure that lasts 5 minutes or more to prevent status epilepticus. Drugs include the sedative lorazepam and the antiseizure drugs phenobarbital, fosphenytoin, or levetiracetam. These drugs are usually given by vein (intravenously). If a drug cannot be given intravenously, diazepam gel may be put into the rectum or midazolam liquid may be put into the nose (intranasally). Diazepam and midazolam are sedatives similar to lorazepam that also stop seizures. Children who have received these drugs or with prolonged seizure or status epilepticus are carefully monitored for problems with breathing and blood pressure.

Prevention

If children have had a febrile seizure, parents should watch for and treat high fevers, which can trigger a seizure. However, a febrile seizure often occurs as the child's temperature increases, or before parents know that the child is ill and recognize the fever.

Drugs to prevent additional seizures (antiseizure drugs—see 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 who have had a long febrile seizure have a subsequent seizure that lasts more than 5 minutes, doctors may give a prescription for diazepam gel to be put into the rectum. Children can be treated with this drug at home.

Drugs Mentioned In This Article

Generic Name Select Brand Names
No US brand name
KEPPRA
CEREBYX
ATIVAN
VALIUM
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