Febrile Seizures

• Developmental threshold hypothesis: The immature brain has an inherently lower seizure threshold compared to older children and adults. This is attributed to: (1) incomplete myelination of inhibitory GABAergic pathways; (2) relative predominance of excitatory glutamatergic transmission; (3) heightened synaptic plasticity; (4) incomplete development of inhibitory interneuron networks in the hippocampus and temporal lobe; and (5) increased expression of NMDA receptors relative to AMPA receptors, potentiating excitatory neurotransmission. The maturation of cortical inhibitory circuits, particularly those mediated by GABA-A receptors, gradually increases seizure threshold with advancing age, explaining the characteristic age-limited nature of febrile seizures.

• Fever-induced neuronal instability: Elevated temperature directly impairs neuronal function through multiple mechanisms: (1) increased metabolic rate exceeding oxygen and glucose delivery, creating an energy deficit state; (2) impaired ion pump function (Na⁺/K⁺-ATPase) due to reduced ATP availability, leading to membrane depolarization; (3) accelerated neurotransmitter release from presynaptic terminals, increasing glutamate and aspartate in the synaptic cleft; (4) temperature-dependent changes in GABA receptor kinetics, reducing inhibitory synaptic efficacy; (5) altered distribution of intracellular calcium, triggering excitotoxic cascades; and (6) increased blood-brain barrier permeability with cytokine infiltration. The relationship between seizure risk and absolute temperature is nonlinear—seizures may occur during the rising phase of fever rather than at peak temperature, suggesting that the rate of temperature change, not absolute temperature, is the critical trigger.

• Genetic predisposition and ion channelopathies: Family history is present in 25-40% of febrile seizure cases, indicating significant genetic contribution. Mutations in genes encoding voltage-gated ion channels have been identified in families with familial febrile seizures (FFS): (1) SCN1A mutations (sodium channel Nav1.1) account for autosomal dominant generalized epilepsy with febrile seizures plus (GEFS+); (2) GABRG2 mutations affecting the gamma-2 subunit of GABA-A receptors impair inhibitory neurotransmission; (3) SCN1B and GABRE mutations further implicate channelopathies in seizure susceptibility. These genetic variants likely lower the seizure threshold synergistically with developmental and fever-related factors. Genome-wide association studies (GWAS) have identified common variants in PCDH15, PYHIN1, and other loci with modest effect sizes, suggesting a polygenic inheritance pattern for common febrile seizures.

• Cytokine-mediated inflammation: Systemic infections triggering fever activate innate immune responses with release of pro-inflammatory cytokines including IL-1β, IL-6, TNF-α, and IL-18. These cytokines cross the blood-brain barrier and directly modulate neuronal excitability: (1) IL-1β potentiates NMDA receptor signaling and reduces GABA-A receptor function; (2) TNF-α increases surface expression of AMPA receptors, enhancing excitatory transmission; (3) cytokine-induced prostaglandin E2 and TGF-β signaling further impairs inhibition. Notably, infections that cause febrile seizures (predominantly viral rather than bacterial) may have particularly strong immune-stimulatory properties, potentially explaining the higher seizure risk with certain pathogens.

• Viral infections (70-80% of cases): The most common precipitants are upper respiratory tract infections (URIs) and otitis media, typically caused by respiratory syncytial virus (RSV), parainfluenza, influenza, adenovirus, and rhinovirus. Other common viral triggers include roseola infantum (HHV-6), which classically presents with high fever followed by a rose-pink maculopapular rash as fever resolves ("fever then rash" pattern); enteroviral infections; varicella zoster virus; and rubeola. Viral infections are associated with higher seizure risk than bacterial infections, possibly due to stronger systemic inflammatory responses or direct neurotropic effects.

• Bacterial infections: Otitis media is the most common bacterial cause, followed by urinary tract infections (UTIs), pneumonia, and meningitis (which, if present, requires different management as this represents a provoked seizure secondary to CNS infection rather than a true febrile seizure). The distinction is crucial: if meningitis is suspected based on clinical findings (nuchal rigidity, petechial rash, altered mental status), the patient requires lumbar puncture and IV antibiotics, not febrile seizure management.

• Age 6 months to 5 years: Peak incidence occurs between 12-18 months. The developmental window reflects the immaturity of inhibitory circuits. Seizures occurring before 6 months or after 6 years of age require different diagnostic consideration (likely indicating unprovoked seizure disorder or alternative etiology).

• Genetic predisposition: Positive family history of febrile seizures in first-degree relatives increases recurrence risk to 30-40% compared to 15-30% baseline. Family history of afebrile seizures or epilepsy is a risk factor for later unprovoked seizure development and should raise suspicion for underlying epilepsy.

• Temperature ≥39°C (102.2°F): Higher absolute fever temperature correlates with increased seizure risk, though the rapid rise in temperature may be more significant than absolute peak temperature.

• Rapid fever onset: Infections with acute fever onset (as opposed to gradual fever escalation) carry higher seizure risk.

• Iron deficiency anemia: Epidemiological studies show increased risk in iron-deficient children, possibly due to reduced seizure threshold or impaired immune function. This has become less relevant in developed countries with fortified foods but remains significant globally.

• Recent immunizations: Retrospective studies suggest a potential association between DPT (diphtheria-pertussis-tetanus) and MMR vaccines and febrile seizures occurring within 24-48 hours, though the risk is small and must be weighed against vaccine benefits. Some guidelines recommend timing of acetaminophen or ibuprofen administration around vaccination in high-risk children.

• Developmental delay or neurodevelopmental disorders: Mild developmental delay increases febrile seizure risk approximately 2-fold, though febrile seizures themselves do not impair neurodevelopment.

• Generalized tonic-clonic seizure (most common, ~60% of cases): The child experiences sudden loss of consciousness coinciding with fever, followed by characteristic progression: (1) tonic phase lasting 30 seconds to 1 minute with sustained muscle contraction, rigidity, and possible flexion or extension of extremities; (2) clonic phase with rhythmic jerking movements of limbs and trunk, typically lasting 1-2 minutes. Associated features include opisthotonus (backward arching), loss of bladder/bowel control with incontinence, and possible cyanosis from apnea during the seizure. Postictal confusion, lethargy, and headache follow, lasting minutes to hours.

• Simple febrile seizure (70% of cases): Defined as generalized seizure, duration <15 minutes, occurring once during a 24-hour febrile illness, without focal features. Recovery is complete and prompt. The absence of focal motor findings (e.g., sustained unilateral jerking, Todd's paralysis) supports the diagnosis.

• Complex febrile seizure (30% of cases): Characterized by focal seizure activity (e.g., repeated clonic jerking of one arm), prolonged duration (≥15 minutes), or multiple seizures within a 24-hour period (recurrence within same febrile episode). Complex febrile seizures carry mildly increased risk of future unprovoked seizures but are not considered status epilepticus unless duration exceeds 30 minutes.

• Fever (usually 38.5-39.5°C): The seizure typically occurs during the rising phase of fever or within hours of fever onset. In some cases, the seizure may be the initial manifestation of illness, with parents unaware of the fever until after seizure onset.

• Physical exam findings:
• Elevated body temperature by rectal or core measurement
• Signs of viral infection: erythematous pharynx, rhinorrhea, cough, rash (variable depending on underlying infection)
• Normal neurological exam post-ictal: Reassuring findings include normal mental status after full recovery, normal motor and sensory examination, and normal reflexes. Any focal neurological deficit warrants investigation for alternative diagnosis.
• Absence of meningeal signs: Absence of nuchal rigidity or Kernig's sign helps exclude meningitis, though young children may not demonstrate classic meningeal signs even with CNS infection.

• Important clinical variants:
• Febrile status epilepticus: Seizure duration exceeding 30 minutes or multiple seizures without intervening consciousness within a 24-hour period. This represents a medical emergency requiring IV antiepileptic medication and is associated with higher risk of future unprovoked seizures.
• Atypical febrile seizure: Focal features, very brief duration (<5 seconds), or seizure occurring without documented fever ("febrile seizure provoked by fever from infection that was not clinically recognized").

• Clinical diagnosis based on characteristic presentation: Febrile seizures are diagnosed clinically when the following criteria are met: (1) age 6 months to 6 years; (2) presence of fever (≥38.0°C); (3) absence of intracranial infection (meningitis, encephalitis); (4) no prior history of unprovoked seizures; and (5) generalized seizure lasting <15 minutes (for simple febrile seizures). This diagnosis can be made at bedside without additional testing in the uncomplicated case.

• Careful history from witnesses or caregivers to establish:
• Precise timing and prodrome: Was fever present before seizure or only recognized after? Did the child have typical URI symptoms?
• Seizure semiology: Generalized versus focal onset? Unilateral versus bilateral jerking? Duration? Number of seizures in this febrile episode?
• Postictal recovery: Was return to baseline alertness prompt (within 30 minutes)? Or was there prolonged altered mental status suggesting alternative diagnosis?
• Previous seizures: Any unprovoked seizures, developmental delay, or family history of epilepsy?
• Recent trauma: Rule out head injury as alternative cause of seizure
• Toxin or medication exposure: History of accidental ingestion

• Physical examination pearls:
• Meningeal signs: Absence of nuchal rigidity and Kernig's sign argues against meningitis, though sensitivity is only 50-70% in young children. Presence of either sign mandates lumbar puncture.
• Rash character and distribution: Petechial or purpuric rash suggests meningococcemia (requires IV antibiotics and droplet precautions); rose-pink maculopapular rash with clear trunk involvement suggests roseola (self-limited); vesicular rash suggests varicella.
• Focal neurological deficits: Todd's paralysis (transient focal weakness post-ictal) or persistent focal weakness, speech abnormalities, or visual field deficits suggest alternative diagnosis.
• Signs of CNS infection: Altered mental status, decreased responsiveness beyond expected postictal state, bulging fontanelle (in infants), or opisthotonus with consciousness preserved.

• Laboratory testing:
• Lumbar puncture: Indicated if clinical suspicion for meningitis or encephalitis is present (nuchal rigidity, petechial rash, altered consciousness, focal neurological signs, age <12 months where meningeal signs are unreliable). NOT routinely recommended for uncomplicated febrile seizure in child >18 months with typical presentation. Consider in children 12-18 months if vaccination status unknown or concern for meningitis exists. CSF analysis would show normal white blood cell count (<5/μL), normal glucose (40-80 mg/dL), and normal protein (15-40 mg/dL) in febrile seizure without CNS infection.
• Blood culture: Not indicated unless clinical signs of bacteremia present (meningococcemia, occult bacteremia).
• Urinalysis and urine culture: Obtain if signs of UTI present (dysuria, frequency, suprapubic tenderness) or fever without clear source in child <24 months, as UTI is a common precipitant and may present without urinary symptoms in young children.
• Complete blood count: Not routinely necessary; may show leukocytosis supporting viral or bacterial infection but does not change management.
• Metabolic panel, calcium, magnesium: Not indicated unless clinical signs of metabolic derangement (altered mental status, tetany) present, as hypocalcemia or hypomagnesemia are rare precipitants in developed countries with adequate nutrition.

• Electroencephalography (EEG):
• NOT routinely recommended following simple febrile seizure. American Academy of Pediatrics (AAP) guidelines do not support routine EEG after uncomplicated febrile seizure as findings do not correlate with recurrence risk or prognosis.
• Consider for complex febrile seizure (recurrent seizures in same febrile episode, focal features, duration >15 minutes) to assess for evidence of focal abnormality or underlying epilepsy.
• Obtain urgently if the patient has not returned to baseline mental status within 1 hour post-seizure, suggesting prolonged postictal state or alternative diagnosis (encephalitis, brain imaging abnormality).

• Neuroimaging (head CT or MRI):
• NOT indicated after simple febrile seizure in child with normal neurological examination and no focal findings. Febrile seizure itself does not cause structural brain abnormality.
• Consider for complex febrile seizure, especially with focal features or abnormal neurological examination, to exclude structural lesion (focal cortical dysplasia, tumor, vascular malformation).
• Obtain urgently if clinical concern for acute intracranial process (subdural hematoma from occult abuse, acute stroke, brain abscess) based on examination findings or history of trauma.

• Differential diagnosis considerations:
• Meningitis: Distinguish by presence of meningeal signs, altered consciousness or lethargy, petechial rash, or abnormal CSF (elevated WBC, protein, low glucose). Requires LP and IV antibiotics.
• Encephalitis: Similar to meningitis but may have more prominent behavioral changes, confusion, hallucinations, or focal neurological deficits. LP shows CSF lymphocytosis with normal glucose. Brain imaging may show temporal lobe involvement (HSV) or other focal abnormalities.
• Unprovoked seizure/epilepsy: Seizure occurring WITHOUT fever or in child <6 months or >6 years age. Family history of afebrile seizures, prior unprovoked seizure, or focal features increase probability. These children require longer-term evaluation and possible antiepileptic therapy.
• Breath-holding spell: Triggered by anger, pain, or frustration (not fever); child holds breath leading to hypoxia and brief loss of consciousness with possible mild jer

Acute stabilisation (seizure still occurring)

• ABCs and positioning: place the child in the lateral recumbent (recovery) position, suction secretions, give supplemental oxygen, and check a point-of-care glucose. Nothing in the mouth; padded protection from injury only. Most febrile seizures are self-terminating within 1–3 minutes and need no drug.
• Benzodiazepines (first-line abortive): indicated once the seizure exceeds ~5 minutes, the operational threshold for status epilepticus in the American Epilepsy Society status epilepticus guideline. They enhance GABA-A chloride conductance, restoring the inhibition that fever has degraded. Route follows access: IV lorazepam, or without IV access rectal diazepam or buccal/intranasal midazolam — the latter two are what families are sent home with as a rescue medication.
• Second-line (benzodiazepine-refractory): a non-benzodiazepine antiseizure medication — levetiracetam, fosphenytoin, or valproate. The AES guideline treats these as reasonable alternatives to one another, and the ESETT trial found no difference in seizure cessation among them. Escalation beyond this is anesthetic-dose infusion in the ICU.

Treating the underlying illness

• Source control: identify and treat the febrile illness itself (otitis media, UTI, pneumonia). If meningitis is suspected, LP and empiric IV antibiotics take precedence — that is a provoked seizure, not a febrile seizure.
• Antipyretics (acetaminophen, ibuprofen) for comfort only. Per the AAP long-term management guideline, scheduled antipyretics do not prevent recurrence.

What not to do

• No continuous prophylactic antiseizure medication after simple febrile seizures (AAP): phenobarbital, valproate, and phenytoin carry cognitive, behavioral, hepatic, and hematologic toxicity that outweighs any benefit in a benign, self-limited condition.
• Intermittent oral diazepam at fever onset reduces recurrence but is reserved for rare high-anxiety or high-recurrence situations because of sedation and ataxia.
• Avoid aspirin in febrile children (Reye syndrome).
• There is no surgical management. The definitive intervention is parental education: seizure first aid, when to call 911, and the reassuring natural history.

Complications of the seizure itself

• Recurrent febrile seizures: roughly one-third of children have another, mechanism being persistence of the same age-dependent low seizure threshold. Risk is highest with onset before 12 months, a relatively low peak temperature at the index seizure, a short fever-to-seizure interval, and a positive family history. Signals as a second event during the same or a later febrile illness.
• Febrile status epilepticus (emergency): seizure >30 minutes or serial seizures without recovery of consciousness. Sustained excitotoxic calcium influx plus benzodiazepine pharmacoresistance (GABA-A receptor internalisation with prolonged seizing) makes this progressively harder to abort. Signalled by ongoing convulsion, failure to regain consciousness, hyperthermia, and lactic acidosis.
• Hippocampal injury and mesial temporal sclerosis: prolonged febrile seizures have been associated on MRI with acute hippocampal edema evolving to sclerosis (the FEBSTAT cohort), the presumed substrate for later temporal lobe epilepsy. Signal: focal prolonged seizure followed by hippocampal T2 signal change.
• Later unprovoked epilepsy: a small absolute increase over the general-population baseline after a simple febrile seizure; higher with complex features, neurodevelopmental abnormality, or family history of epilepsy.
• Aspiration, hypoxia, and traumatic injury (emergency): loss of airway protection during the tonic-clonic phase; signalled by cyanosis, post-ictal hypoxemia, or a new infiltrate on chest radiograph.
• Missed bacterial meningitis (emergency): the seizure is attributed to fever while CNS infection is the real cause. Red flags are failure to return to baseline, meningeal signs, bulging fontanelle, petechiae, or incomplete Hib/pneumococcal immunisation — obtain LP.

Complications of treatment

• Benzodiazepines: dose-dependent respiratory depression, hypotension, and prolonged sedation that obscures neurologic reassessment — an airway emergency; watch capnography and saturations.
• Valproate: hepatotoxicity (highest risk under 2 years, especially with mitochondrial disease/*POLG*) and pancreatitis; signalled by vomiting, lethargy, rising transaminases or ammonia.
• Phenobarbital: sedation, hyperactivity, and cognitive/behavioral impairment — a key reason the AAP rejects daily prophylaxis.
• Aspirin: Reye syndrome — encephalopathy with hepatic steatosis.

• The definition is the whole question: simple = generalized, <15 minutes, once in 24 hours, in a child 6 months–5 years with fever and no CNS infection. Any focality, ≥15 minutes, or recurrence within 24 hours makes it complex.
• Single best next step after a simple febrile seizure in a well-appearing, fully immunised, back-to-baseline child: look for the source of fever and reassure. Not EEG, not CT, not routine LP — the AAP neurodiagnostic guideline explicitly advises against them.
• When to do the LP: meningeal signs, altered mental status or failure to return to baseline, petechial/purpuric rash, incomplete or unknown Hib and pneumococcal immunisation, or recent antibiotics that could partially treat meningitis (masking the CSF picture). Young infants are the highest-risk group because meningeal signs are unreliable.
• The classic association examiners test: roseola infantum (HHV-6) — high fever for days, seizure, then a rose-pink maculopapular rash appearing as the fever breaks.
• The commonest distractor: scheduled acetaminophen or ibuprofen to prevent recurrence. Antipyretics improve comfort only; the AAP states they do not reduce febrile seizure recurrence. Equally wrong is starting daily phenobarbital or valproate.
• Recurrence versus epilepsy are different risk sets: recurrence is driven by young age at onset, low peak temperature, short fever-to-seizure interval, and family history of febrile seizures. Later epilepsy is driven by complex features, neurodevelopmental abnormality, and family history of afebrile seizures.
• Prolonged or focal febrile seizures in infancy, later joined by afebrile seizures: think SCN1A channelopathy — GEFS+ or Dravet syndrome. Sodium-channel blockers such as carbamazepine and lamotrigine worsen Dravet.
• The rescue prescription: families of children with prolonged or recurrent events go home with rectal diazepam or intranasal/buccal midazolam, with instructions to use it at the 5-minute mark and call 911.
• Prognosis line to memorise: simple febrile seizures do not cause brain damage, developmental delay, or death, and normal children do not need restriction of activity.