Febrile Seizures

Fever and seizures most commonly occur together as febrile seizures, but the combination also occurs with meningitis or underlying epilepsy — don’t assume febrile seizure without considering these. See also febrile child.

Key points

1. Most febrile seizures are benign and need no investigation.
2. Identify and treat the fever source if indicated.
3. Antipyretics do not reduce the risk of further febrile seizures.

Classification

• Simple febrile seizure (all of): generalised tonic-clonic; duration <15 min; recovery <1 hr; does not recur within the same illness.
• Complex febrile seizure (any of): focal features at onset or during the seizure; duration >15 min; incomplete recovery within 1 hr; recurrence within the same illness.
• Afebrile “febrile” seizure — a seizure during an acute infectious illness (usually gastroenteritis) without a documented fever, otherwise consistent with a simple febrile seizure.
• Prolonged febrile seizure: duration >30 minutes (i.e. febrile status epilepticus) — uncommon (occurs in <10% of children at their first febrile seizure), associated with worse outcomes, and may be associated with a genetic epilepsy syndrome.

Epidemiology

~3% of the population; ages 5 months–5 years (most in the first 2 years), peaking at 12–18 months, with a slight male predominance. ~⅓ recur. Recurrence risk: 50% if the first seizure was in infancy (<1 year) or there’s a family history of febrile seizures; 30% if the first seizure was at age 2. Around 80% of febrile seizures occur with a viral (rather than bacterial) infection — roseolovirus is the single most common cause in children under 2, and is itself associated with a higher rate of complex/recurrent seizures and febrile status epilepticus.

Epilepsy risk is tiered, not a single flat figure. After a simple febrile seizure, ~1–2% of children later develop epilepsy — only slightly above the ~0.5–0.9% background population risk. After a complex febrile seizure the risk rises to ~2–10%, scaling with how many of the following are present: earlier age at first seizure, prolonged seizure, abnormal neurodevelopment, an abnormal EEG, or a family history of epilepsy. Genetic testing may be worth considering in higher-risk groups: a prolonged febrile seizure in a child <18 months, febrile seizures starting after age 6, or associated developmental impairment.

History — features against a simple febrile seizure

Age <6 months (consider CNS infection); age >6 years (consider epilepsy); focal neurological features at onset, or a prolonged seizure; signs of CNS infection (e.g. vomiting); progressive neurological conditions; developmental delay or regression; previous afebrile seizures. Also screen for: meningism (bulging fontanelle, neck stiffness, photophobia), persistent altered consciousness beyond 1 hour, seizure mimickers (cardiac dysrhythmia, metabolic disturbance), a family history of epilepsy or sudden cardiac death, and neurocutaneous stigmata on examination (a unilateral facial port-wine stain, facial angiofibroma, hypopigmented macules, or café-au-lait spots) that might point to an underlying neurocutaneous syndrome rather than a simple febrile seizure.

Investigations

No role for investigation if the infection source is clinically localised — a simple febrile seizure needs nothing beyond whatever the fever itself warrants; extra bloods and neuroimaging are low-yield and expose the child to an unnecessary painful procedure and/or radiation. Otherwise, investigate as per febrile child. Targeted investigations are reserved for atypical presentations or a complex febrile seizure: BGL and electrolytes to exclude a provoked seizure, an ECG to exclude a seizure mimicker, and — after discussion with a senior doctor — CNS imaging if there’s raised intracranial pressure, a focal neurological abnormality, a suspected structural brain lesion, an enlarged head, or a severe head injury. Lumbar puncture is not needed for a simple febrile seizure with rapid return to baseline, but should be considered for signs of CNS infection, an infant under 12 months, incomplete immunisation against Streptococcus pneumoniae or Haemophilus influenzae type B, a seizure occurring 2 or more days after fever onset, or current antibiotics (which can mask meningitis).

Acute seizure management

Establish airway + give O₂; call an ambulance; attempt IV access; check BGL (treat if <3 mmol/L).

If the seizure lasts ≥5 minutes:

• Midazolam 0.15 mg/kg IM, or 0.3 mg/kg buccal/intranasal (max 10 mg).
• Repeat after 5 minutes if still seizing.
• Then IV phenytoin 20 mg/kg (or phenobarbitone 20 mg/kg if already on phenytoin/already trialled) — over 20 minutes.
• If still seizing, levetiracetam 20 mg/kg IV/IO (max 1.5 g) over 15 minutes is an option with more limited evidence.

Maintain continuous ECG/respiratory rate/oximetry monitoring throughout. A child not improving in conscious state as expected after apparent seizure termination may be in subclinical status — escalate via local emergency protocols. In children <2 years still fitting, consider pyridoxine- dependent seizures.

Disposition and follow-up

Consult the local paediatric team for a complex febrile seizure, or if there’s concern for a serious bacterial infection as the cause. Consider transfer for respiratory or haemodynamic compromise, a prolonged febrile seizure, or persistent altered consciousness beyond 1 hour. Before discharge (once neurologically back to baseline and the underlying illness is assessed/managed), give seizure first-aid education, and — if the seizure lasted >5 minutes — consider an emergency medication management plan with parent midazolam training. Consider outpatient paediatric follow-up (may include EEG, neuroimaging, genetic testing) when risk factors for epilepsy are present: a prolonged febrile seizure, family history of epilepsy, neurocutaneous stigmata, recurrent complex febrile seizures, or developmental impairment.

Long-term outlook is reassuring. Febrile seizures don’t cause long-term neurological or cognitive harm, and a single episode isn’t linked to learning disability, lower intelligence, or behavioural problems — most children have entirely normal developmental outcomes. Recurrent febrile seizures may carry a small increased risk of delayed vocabulary development, but nothing more.