Febrile seizures

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Chapter 17 FEBRILE SEIZURES

Jonathan M. Wong

General Discussion

Febrile seizures are common, occurring in 2% to 5% of children in North America at least once in their lifetime. Most of these (65% to 90%) are “simple” febrile seizures (see below). The typical age for febrile seizures ranges from 6 months to 5 years, with a peak occurrence at 18 to 24 months of age.

In 1993, the International League Against Epilepsy defined a febrile seizure as “an epileptic seizure occurring in childhood associated with fever, but without evidence of intracranial infection or defined cause. Seizures with fever in children who have experienced a previous non-febrile seizure are excluded.” The evaluation of a febrile seizure is based upon the nature of the seizure and the underlying illness triggering the fever.

Febrile seizures can be classified as either simple or complex. Simple febrile seizures last less than 15 minutes, occur once in a 24-hour period, are generalized, or occur in children with no previous neurologic problems. Complex febrile seizures last 15 minutes or longer, occur more than once in a 24-hour period, are focal, or occur in a patient with known neurologic problems such as cerebral palsy.

Although they are frightening, febrile seizures for the most part are benign events. The recurrence rate is approximately 33%. The rate of developing epilepsy is only slightly increased compared with the general population, especially if there are no major risk factors for developing epilepsy. Attention should be paid to relieving parental anxiety and reassuring them of the benign nature of febrile seizures. Parents should be taught what to do in case of a recurrent seizure regarding supportive care and preserving the airway.

Continuous therapy after a febrile seizure is not effective in reducing the development of afebrile seizures. Furthermore, current guidelines do not recommend the use of continuous or intermittent therapy with neuroleptics or benzodiazepines after a simple febrile seizure.

Risk factors for febrile seizure include daycare attendance, developmental delay, a first- or second-degree relative with history of febrile seizure, a history of a neonatal nursery stay of more than 30 days, and male sex (1.4:1 risk). In children with a febrile illness, the height of the fever, the rate of development of the fever, and a family history of febrile seizure affect the likelihood of having a febrile seizure; 10% of siblings and 10% of offspring of a person with febrile seizures in childhood will have a febrile seizure.

Risk factors for recurrent febrile seizure include age younger than 18 months of age at first febrile seizure, short duration of the fever before onset of fever, family history of epilepsy, family history of febrile seizures, and the height of the fever.

Risk factors for the development of afebrile seizures after an episode of febrile seizure include a complex febrile seizure, duration of fever less than 1 hour before onset of febrile seizure, family history of epilepsy, and neurodevelopmental abnormalities such as cerebral palsy or hydrocephalus.

Suggested Work-Up

A work-up is generally unnecessary unless an evaluation for a source of fever is indicated. The American Academy of Pediatrics recommends that the following determinations not be performed routinely in the evaluation of a first simple febrile seizure: serum electrolytes, calcium, phosphorus, magnesium, complete blood cell count (CBC), or blood glucose. If vomiting and diarrhea accompany a febrile seizure, an assessment of electrolyte concentrations and serum glucose levels may be required. However, the following laboratory tests may be indicated in certain circumstances:

Lumbar puncture with cerebrospinal fluid analysis	Should be considered in children younger than 18 months because meningeal signs are less reliable in this group. Lumbar puncture should also be considered if the patient’s mental status is not improving. Lumbar puncture is recommended in infants younger than 12 months after the first seizure with fever.
CBC with differential	May be indicated in the evaluation of the underlying infection
Serum electrolytes	To evaluate for electrolyte derangement, especially if the patient has diarrhea or vomiting
Glucose	If hypoglycemia or hyperglycemia is suspected
Calcium and magnesium	If calcium or magnesium derangement is suspected
Toxicology screen	To evaluate for drug ingestion if indicated by history or if alcohol intoxication is suspected
Neuroimaging (magnetic resonance imaging [MRI] is the preferred modality)	The American Academy of Pediatrics recommends that neuroimaging not be performed in the routine evaluation of the child with a first simple febrile seizure.However, neuroimaging is indicated in a child with a febrile seizure and evidence of increased intracranial pressure or a history or physical examination suggestive of trauma. Also indicated in cases of possible structural defects (e.g., in cases of microencephaly or spasticity).

Electroencephalography has not been found to be helpful in predicting the likelihood of developing epilepsy later in life.

Additional Work-Up

Several studies have examined children with febrile seizure for the incidence of bacterial infection, including unsuspected meningitis. None of these studies reported any cases of meningitis (less than 3% had Streptococcus pneumoniae bacteremia, and 3% to 6% had urinary tract infection [UTI]). The absence of any remarkable findings on history or physical examination makes meningitis quite unlikely to be the cause of fever and subsequent seizure.

1. Baumann R.J. Technical report: treatment of the child with simple febrile seizures. Pediatrics. 1999;103:86.

2. Committee on Quality Improvement, Subcommittee on Febrile Seizures. Practice parameter: long-term treatment of the child with simple febrile seizures. Pediatrics. 1999;103:1307–1309.

3. Duffner P.K., Baumann R.J. A synopsis of the American Academy of Pediatrics’ practice parameters on the evaluation and treatment of children with febrile seizures. Pediatr Rev. 1999;20:285–287.

4. Millar J.S. Evaluation and treatment of the child with febrile seizure. Am Fam Physician. 2006;73:1761–1764.

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