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Febrile Seizures
Michael A. Davis, MD
Febrile seizures are the most common convulsive disorder of childhood. A febrile seizure is defined as a seizure associated with fever in infancy or early childhood (usually between 3 months and 5 years of age), without evidence of intracranial infection or other cause.
Febrile seizures are a benign syndrome caused primarily by genetic factors, manifest as an age-related susceptibility to seizures, which eventually is outgrown. The problem almost always resolves without sequelae. Only a small minority will develop non-febrile seizures later. Unless seizures are exceedingly long, there is no risk of brain damage. The majority of children who have febrile seizures require no treatment, other than parental reassurance.
Epidemiology
Febrile seizures occur in 2-4% of young children. The most common age of onset is in the second year of life.
Higher temperature and a history of febrile seizures in a close relative are risk factors for the development of a febrile seizure.
Recurrence
After the first febrile seizure, 33% of children will experience one or more recurrences, and 9% of children who have febrile seizures will have 3 or more.
The younger the child’s age when the first febrile seizure occurs, the greater the likelihood of recurrence.
Family history of febrile seizures is a risk factor for recurrence.
Short duration of fever before the initial seizure and relatively lower fever at the time of the initial seizure are risk factors.
Epilepsy. Fewer than 5% of children who have febrile seizures actually develop epilepsy.
Genetics
Febrile seizures tend to occur in families. The risk of febrile seizures in younger siblings of children who have febrile convulsions is 10-20%, and the risk is higher if the parents have a history of febrile convulsions.
Risk factors for the development of epilepsy following febrile seizures include suspicious or abnormal development before the first seizure, family history of afebrile seizures, and complex first febrile seizure.
Pathophysiology
Most febrile illnesses associated with febrile seizures are caused by common infections (tonsillitis, upper respiratory infections, otitis media).
Children of preschool age are subject to frequent infections and high fevers. These children have a relatively low seizure threshold, resulting in febrile seizures being more common.
Clinical Evaluation
Febrile seizures usually occur early in the course of a febrile illness, often as the first sign. The seizure may be of any type, but the most common is tonic-clonic. Initially there may be a cry, followed by loss of consciousness and muscular rigidity. During this tonic phase, apnea and incontinence may occur. The tonic phase is followed by the clonic phase of repetitive, rhythmic jerking movements, which is then followed by postictal lethargy or sleep.
Other seizure types may be characterized by staring with stiffness or limpness or only focal stiffness or jerking.
Most seizures last less than 6 minutes; 8% last longer than 15 minutes.
An underlying illness that may require treatment should be sought. Symptoms of infection, medication exposure, trauma should be assessed. The developmental level, and family history of febrile or afebrile seizures should be evaluated. A complete description of the seizure should be obtained from a witness.
Physical Examination
The level of consciousness, presence of meningismus, a tense or bulging fontanelle, Kernig or Brudzinski sign, and any focal abnormalities in muscle strength or tone are sought.
Encephalitis or meningitis must be excluded. A lumbar puncture (LP) is indicated if there is any suspicion of meningitis. The presence of a focus of infection (otitis media) does not preclude the possibility of meningitis, and if the infant has been taking antibiotics, partially treated meningitis should be suspected.
Clinical signs of meningitis may be absent in infants younger than 18 months, and the threshold for performing an LP should be low at this age. If increased intracranial pressure is present, an LP may cause fatal brain herniation, and LP is usually contraindicated.
Other causes of seizures associated with fever include roseola infantum, Shigella gastroenteritis, ingestion of diphenhydramine, tricyclic antidepressants, amphetamines, and cocaine, and dehydration-related electrolyte imbalances.
Laboratory studies are not routinely necessary, except as part of the evaluation for a source of fever. Neuroimaging such as a CT or MRI are seldom helpful and are not performed routinely. The electroencephalogram (EEG) is not helpful in the evaluation of febrile seizures because it is not predictive of recurrence risk of later epilepsy.
Management of Febrile Seizures
The child should be kept in the emergency department or physician’s office for at least several hours and re-evaluated. Most children will have improved and be alert, and the child may be sent home if the cause of the fever has been diagnosed and treated. Hospital admission is necessary if the child is unstable or if meningitis remains a possibility.
Parental Counseling
Parents are advised that febrile seizures do not cause brain damage, and the likelihood of developing epilepsy or recurrent non-febrile seizures is very small.
There is a risk of further febrile seizures during the current or subsequent febrile illnesses.
If another seizure occurs, the parent should place the child on his side or abdomen with the face downward. Nothing should be forced between the teeth. If the seizure does not stop after 10 minutes, the child should be brought to the hospital.
Control of fever with antipyretics (acetaminophen) and sponging is recommended, but this practice has not been proven to lower the risk of recurrent febrile seizures.
Childhood Immunizations. Febrile seizures occur most commonly following a pertussis or DPT immunization because pertussis provokes fever. The advantages of vaccines must be weighed against the risk of pertussis if immunization is postponed. The greatest risk for febrile seizure recurrences occurs in the 48 hours following a DPT immunization and 7 to 10 days after a measles immunization.
Long-term Management
Antipyretics alone have not been shown to be effective in preventing febrile seizure recurrences. Prophylaxis with diazepam or phenobarbital may be reserved for very young children who have sustained multiple seizures associated with focal post-ictal paralysis.
Diazepam may be administered orally and rectally during febrile illnesses to prevent recurrences of seizures. Oral diazepam is given in three divided doses to a total of 1 mg/kg per day when the child is ill or feverish. §