Febrile Seizure

Etiology

Febrile seizures occur with a fever higher than 38 C or 100.4 F and no other seizure-provoking etiologies such as described above. The highest fever necessary to cause febrile seizures is specific to the individual as each child's threshold convulsive temperature varies. While the degree of fever is ultimately the most significant factor in febrile seizures, these seizures often occur as the patient's temperature is rising. In fact, a febrile seizure may be the first sign that a child is ill, with the presence of fever greater than 38 degrees discovered shortly after that. There is no specific cause of fever that is more likely to cause febrile seizures, however, viral rather than bacterial infections are most commonly associated with febrile seizures. A particular virus, HHV-6, is most commonly associated with febrile seizures in the United States and European countries. In Asian countries, influenza A virus has been frequently associated with febrile seizures. Any fever of adequate height may cause a febrile seizure.[3][4]

Epidemiology

The exact age constituting a febrile seizure varies slightly throughout medical literature with 6 months to 60 months (5 years) being a common working definition. Febrile seizures are extremely common, occurring in up to 4% of children in this age group. Some children have a single febrile seizure event, and others have multiple events over early childhood.

Pathophysiology

The exact pathophysiology of febrile seizures is not understood. There is a recognized genetic predisposition with 10% to 20% of first-degree relatives of patients with febrile seizures also experiencing febrile seizures. No specific mode of inheritance is known.[5]

History and Physical

A detailed description of the seizure event is essential for the evaluation of a possible febrile seizure patient. Historical information regarding the exact appearance and length of the event is vital. Information regarding the symptoms of a central nervous system (CNS) infection, underlying structural abnormalities, personal history of neurologic problems, personal immunization history, and personal or family history of prior seizure is essential in deciding whether an event of concern constitutes a febrile seizure or rather constitutes a more severe illness presenting with a seizure.

Once a seizure is qualified as a febrile seizure, the examiner should seek additional information to differentiate whether it is simple or complex.

Simple febrile seizures occur more commonly than complex febrile seizures and are characterized by a seizure that is generalized, lasts less than 15 minutes, and does not recur within 24 hours.

Complex febrile seizures are characterized by the presence of at least one of the following features: focality, duration of longer than 15 minutes, and recurrence within a 24-hour period. In either instance, a general physical exam and neurologic exam are necessary. Post-ictal drowsiness is not abnormal in febrile seizures but typically resolves within a few minutes. A patient recovering from a febrile seizure will rapidly return to baseline and towards a normal neurologic exam. If a patient does not return to baseline, remains completely unresponsive to noxious stimuli after the seizure, or has other symptoms of acute neurologic dysfunction before the seizure (such as acute headaches, alteration of mental status, or concern for weakness), other complicating etiologies should be a consideration.

Evaluation

A patient with a normal general and neurologic exam, whose history is consistent with a simple febrile seizure, does not need a further laboratory, imaging, or neurophysiologic evaluation. If a patient's history is consistent with a complex febrile seizure, an electroencephalogram (EEG) is obtained to look for underlying abnormalities that may predispose the patient to seizures. If this initial EEG is abnormal, imaging is the next step. In a complex febrile seizure returning to baseline, often these are outpatient studies.[4][6]

A lumbar puncture may be a consideration in the setting of fever and seizures. For a patient with the appropriate history of a febrile seizure and a rapid return to baseline, no lumbar puncture is necessary. Lumbar puncture is a recommendation when there are signs or symptoms that cause concern of a CNS infection; further, the lumbar puncture should be considered in infants aged 6 months to 12 months without appropriate immunization against Streptococcus pneumoniae or Haemophilus influenza type B and in patients taking antibiotics in which partial treatment may mask meningitis or other CNS infection.

Imaging studies are not indicated for simple febrile seizures.

Treatment / Management

There is no specific treatment for simple or complex febrile seizures other than appropriate treatment for underlying etiologies driving the ongoing febrile illness.  Antipyretics have not been shown to prevent a recurrence of febrile seizures.  In patients who have a frequent recurrence of febrile seizures such as seizures with a majority of febrile illnesses, studies have examined treatment with benzodiazepines as a bridging measure for a few days during subsequent febrile events.[7][8][9]

Febrile status epilepticus can occur in less than 10% of children during the first febrile seizure. Rectal diazepam is used to abort this disorder if it lasts more than 5 minutes. There are also recommendations for intranasal midazolam. Patients with febrile status epilepticus are at risk for future episodes of the same event.

Differential Diagnosis

The differential diagnosis of febrile seizures include:

• Aseptic meningitis
• Bacterial meningitis
• Encephalitis
• Tonic-clonic seizures

Prognosis

About 30% of children with a previous febrile seizure remain at an increased risk of recurrent febrile seizures.

Children less than 12 months at the time of the first febrile seizure have a 50% chance of having a second seizure within the first year. This risk drops to 30% the following year. Other than young age during the first febrile seizure, a family history of febrile seizure, low degree of fever during the seizure, and a shorter interval between fever and the seizure may indicate a higher probability of recurrent febrile seizures. However, features associated with complex febrile seizures do not necessarily increase the risk of recurrence of febrile seizures.

About 1-2% of children with simple febrile seizures - only slightly higher risk than the general population- develop subsequent epilepsy. However, children with complex febrile seizures, abnormal neurodevelopment, or with a family history of epilepsy have a higher risk of epilepsy(approximately 5-10%). 

There is no evidence that febrile seizures are linked to learning disabilities or lower intelligence.