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Febrile seizure

A febrile seizure, also known as a fever fit or febrile convulsion is a generalized convulsion caused by elevated body temperature. They most commonly occur in children below the age of three years old and should not be diagnosed in children under the age of 6 months or over the age of 6 years. In many cases, the first sign of fever is the onset of the seizure. It has been theorized that the seizure is triggered by the rapidity of the rise in temperature, rather than the actual temperature reached. more...

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Febrile seizures represent the meeting point between a low seizure threshold (genetically and age determined) - some children have a greater tendency to have a seizure under certain circumstances - and a trigger: fever. The genetic causes of febrile seizures are still being researched. Some mutations that cause a neuronal hyperexcitability and could be responsible for febrile seizures have already been discovered.

The diagnosis is one that must be arrived at by eliminating more serious causes of seizure: in particular, meningitis and encephalitis must be ruled out. Therefore a doctor's opinon should be sought and in many cases the child would be admitted to hospital overnight for observation and/or tests. As a general rule, if the child returns to a normal state of health soon after the seizure, a nervous system infection it is unlikely. Even in cases where the diagnosis is febrile seizure, doctors will try to identify and treat the source of fever. In particular, it is useful to distinguish the event as a simple febrile seizure - in which the seizure lasts less than 15 minutes, does not recur in the next 24 hours, and involves the entire body. The complex febrile seizure is characterized by long duration, recurrence, or focus on only part of the body. The simple seizure represents the majority of cases and is considered to be less of a cause for concern than the complex. It is reassuring if the cause of seizure can indeed be determined to have been fever, as simple febrile seizures generally do not cause permanent brain injury; do not tend to recur frequently, as children tend to 'out-grow' them; and do not make the development of adult epilepsy significantly more likely.

Children with febrile convulsions who are destined to suffer from afebrile epileptic attacks in the future will usually exhibit the following:

  • A family history of afebrile convulsions in first degree relatives (a parent or sibling)
  • A pre-convulsion history of abnormal neurological signs or developmental delay
  • A febrile convulsion lasting longer than 15 minutes
  • A febrile convulsion with strong indications of focal features before, during or afterward


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Evidence-Based Approach to Febrile Seizures in Children
From American Family Physician, 4/1/02 by Anne D. Walling

Febrile seizures are the most common neurologic disorder in childhood, affecting up to 4 percent of children in the United States and Great Britain. A simple febrile seizure is defined as a generalized seizure occurring once in a 24-hour period, lasting less than 15 minutes, and associated with fever in a neurologically healthy child. Offringa and Moyer reviewed the prevalence of meningitis in children with febrile seizures and the risk of recurrence after a first febrile seizure. The evidence is summarized in the accompanying table on page 1448.

Estimates of the likelihood of meningitis presenting as a childhood febrile seizure are derived from studies of children treated in emergency departments. Based on a review of seven studies in urban hospital emergency departments (2,100 cases), the prevalence is between 1 and 2 percent in the United States. Information from two Dutch hospitals indicates that the prevalence may be as high as 7 percent in the Netherlands (selective referral; up to 50 percent of febrile seizures in that country are managed by general practitioners).

Clinical features are the most useful factors in discriminating between meningitis and other causes of seizure in children. If one or more of the major clinical signs of meningitis--petechiae, nuchal rigidity, and coma--are not present, meningitis is extremely unlikely. In the studies, no cases of meningitis were diagnosed without the presence of at least one of these features. Age, sex, degree of fever, and data from blood tests did not have diagnostic value in the studies. The authors concluded that lumbar puncture should be performed only in children at high risk for meningitis.

Treatment of febrile seizures is focused on preventing recurrence. One trial in children with a mean age of 24 months who had one or more febrile seizures compared diazepam (administered orally every eight hours during febrile illness) with placebo. Over a mean period of two years, the relative annual risk of febrile seizures per child was 0.56. The study found that many parents did not follow treatment instructions. Analysis limited to children who had seizures while receiving the study drug demonstrated an 82 percent risk reduction with diazepam therapy. This benefit must be balanced against the finding that 25 to 30 percent of the children treated with diazepam developed symptoms such as irritability, ataxia, or lethargy.

Older studies of phenobarbital and valproate showed no statistically significant reductions in the recurrence of febrile seizures. Although one meta-analysis found limited benefit from continuously administered prophylactic phenobarbital, eight children would have to be treated for two years to prevent one febrile seizure, and the burden of adverse effects was high. One randomized, placebo-controlled study of ibuprofen given every six hours during fever (temperature higher than 38.4[degrees]C [101.1[degrees]F]) showed no reduction in seizure recurrence.

One large collaborative study involving 1,410 episodes of recurrent seizure in 2,496 children estimated that 32 percent had one recurrence, 15 percent had two recurrences, and 7 percent had three or more recurrences, with 7 percent of the recurrent seizures being complex. The risk of recurrence was greatest between 12 and 24 months of age.

The authors recommended a conservative approach to febrile seizures in low-risk children. They stressed the importance of explanation and discussions with the parents to address their concerns about recurrence. Parents should also be given directions on the rectal administration of diazepam if a seizure lasts more than 15 minutes.

Offringa M, Moyer VA. Evidence based management of seizures associated with fever. BMJ November 10, 2001; 323:1111-4.

COPYRIGHT 2002 American Academy of Family Physicians
COPYRIGHT 2002 Gale Group

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