17.1 Febrile Seizures

Febrile Seizures

Febrile seizures are seizures triggered by fever (temperature of 38C/100.4F or higher) in children between 6 months and 5 years of age, occurring without evidence of central nervous system (CNS) infection, a prior afebrile seizure, or an acute metabolic derangement. They are extremely common, affecting roughly 2-5% of children, and are one of the most frequently tested "benign" pediatric neurology topics on Part 1 written exams because the correct answer usually hinges on distinguishing appropriate reassurance from genuine red flags. Peak incidence is 12-18 months; febrile seizures are uncommon before 6 months of age (favor CNS infection or a metabolic/genetic cause instead) and become progressively less likely after age 5, when the differential shifts toward epilepsy provoked by fever.

Simple vs. Complex: The Core Distinction

Exam trap: a single episode needs only one complex feature (focality, duration of 15 minutes or longer, or recurrence within the same illness) to be reclassified as complex, even if the other two criteria look simple. Febrile status epilepticus, a febrile seizure lasting 30 minutes or longer (or repeated seizures without recovery of consciousness for 30 minutes), is the most severe subtype of complex febrile seizure and carries the highest risk of later epilepsy.

When Does This Child Need a Lumbar Puncture?

The exam wants you to know that a child does not need a lumbar puncture (LP) simply because they had a febrile seizure; the decision is driven by clinical suspicion of meningitis, not by the seizure itself. General board-style guidance includes:

• Any age with meningeal signs: neck stiffness, a bulging fontanelle, a positive Kernig or Brudzinski sign, or persistently altered mental status after the postictal period resolves should prompt an LP regardless of age.
• Infant 6-12 months: LP should be strongly considered if immunization status against Haemophilus influenzae type b and Streptococcus pneumoniae is incomplete or unknown, since infants in this age range can have subtle or absent classic meningeal signs.
• Infant pretreated with antibiotics: prior oral antibiotic therapy can partially treat and mask evolving bacterial meningitis, lowering the threshold for LP.
• Complex febrile seizure with a prolonged postictal state: consider LP if the child does not return to a normal, interactive baseline within the expected timeframe.
• Well-appearing, fully immunized child 12 months or older with a simple febrile seizure who returns quickly to baseline: LP is not routinely indicated.

Routine electroencephalogram (EEG) and neuroimaging are not indicated after a simple febrile seizure; they do not change management and are a classic distractor answer on this exam. Blood glucose, electrolytes, calcium, and complete blood count (CBC) are also not routinely needed unless clinically indicated by history or exam. The workup should instead focus on identifying the source of the fever (otitis media, a viral upper respiratory infection, roseola, urinary tract infection (UTI), and so on), since the seizure is a response to the height or rate of temperature rise, not to any specific pathogen.

Recurrence Risk

Roughly 30-40% of children will have at least one recurrent febrile seizure, and about half of those will go on to have a third episode. Recognized risk factors for recurrence include:

• Young age at the first febrile seizure (younger than 12-18 months)
• Family history of febrile seizures in a first-degree relative
• Lower peak temperature at the time of the seizure (the seizure occurred at a relatively low fever)
• Shorter duration between fever onset and the seizure
• Daycare attendance (more frequent febrile illnesses)

Recurrence risk is not meaningfully reduced by prophylactic antipyretics; antipyretics improve comfort but do not prevent a febrile seizure, a point tested repeatedly because it is counterintuitive to worried families and sometimes to trainees.

Prognosis: Epilepsy Risk Is Low

This is the single most important takeaway for the exam: febrile seizures, especially simple ones, do not cause brain damage and do not meaningfully increase the risk of future epilepsy above a low baseline.

• After a simple febrile seizure, the risk of subsequently developing epilepsy is only slightly above the general population risk (roughly 1-2% versus about 1%).
• After a complex febrile seizure, particularly with multiple complex features, febrile status epilepticus, a family history of epilepsy, or a preexisting neurodevelopmental abnormality, risk rises further (commonly cited ranges of roughly 4-15% depending on how many risk factors are present).
• Febrile seizures do not lower intelligence quotient (IQ), and they do not worsen school performance or behavior on long-term follow-up.

Because the prognosis is favorable and recurrence does not predict later epilepsy, daily maintenance antiepileptic therapy is not recommended after simple or even most complex febrile seizures. For a child with frequent or prolonged recurrences, a rescue benzodiazepine (rectal diazepam or intranasal/buccal midazolam) given at home for any seizure lasting beyond about 5 minutes is a more appropriate strategy than daily prophylaxis. Parent education, including how to time a seizure, positioning the child safely on their side, and recognizing when to call emergency services (seizure lasting more than 5 minutes, difficulty breathing, or failure to return to baseline), is a recurring next-step answer on this exam.