Febrile seizures are seizures associated with fever (> 37.8 C), and not due to underlying pathology such as epilepsy or infection.
They are common in children aged 6 months to 5 years old. It peaks at 12 – 18 months. It is benign, affecting 3 – 5 % of children.
Definition of terms
| Term | Definition |
|---|---|
| Febrile status epilepticus | A complex febrile seizure that lasts longer than 30 minute or by shorter serial seizures without regaining consciousness in the interictal state |
| Meyer’s hypothesis | The immature brain has enhanced excitatory neurotransmission (primarily glutamate-mediated) and underdeveloped inhibitory neurotransmission (mainly GABAergic). When a febrile illness causes a rapid rise in temperature, it further disrupts this balance, lowering the seizure threshold and leading to convulsions. |
Simple vs Complex febrile seizure
| Simple febrile seizure | Complex febrile seizure | |
|---|---|---|
| Seizures per febrile episode | One | More than One |
| Duration | < 15 min | > 15 min |
| Characteristic | Generalized – tonic clonic | Focal or generalized, and prolonged |
| Recurrence | Does not recur in a 24 hour period | Recurs within a 24 hour period |
| Post-ictal phase | Short | Long and associated with deficits e.g. Todds palsy |
- Causes of febrile convulsions
- Viral infections (80%)
- Infection with HHV 6 – Roseola infantum (Sixth disease)
- Respiratory tract infection
- Otitis media
- Urinary tract infection
- Influenza
- Immunization with Measles or MMR or MMRV
- Iron deficiency (ferritin < 30 mcg/L)
- Genetics
- Sodium channel mutations
- GABA channel mutations
- Increased production of fever mediators
- Viral infections (80%)
- Patient History
- Fever > 37.8 C
- No history of previous afebrile seizure
- Signs and symptoms
- Fever
- Simple febrile convulsion in most patients
- Generalised tonic-clonic seizure
- Muscle stiffness and jerking or shaking of the limbs
- No focal features
- Seizures last about 10 minutes
- Occurs only once within 24 hours or within the same febrile illness
- Resolves spontaneously
- Post-ictal drowsiness and confusion lasting several minutes to hours
- Comlex febrile convulsions
- Focal features, e.g., movement of one side of the body only
- Lasts more than 15 minutes
- Recures within 24 hours or within the same illness
- Prolonged post-ictal period
- Breathing difficulties
- Pallor
- Cyanosis
- Loss of consciousness
- Differentials
- Epilepsy
- Viral meningitis
- Bacterial meningitis
- Acute encephalopathy
- Dravet syndrome
- Investigations
- Blood glucose to rule out hypoglycaemia
- Serum sodium to rule out hyponatraemia . Hyponatraemia increases the risk of recurrence (avoid hypotonic fluids)
- Lumbar puncture: if the infant is < 6 months or symptoms are suggestive of CNS infection
- Urine culture: if > 18 months of age or complex seizure
- EEG: to differentiate non-convulsive status vs prolonged post-ictal state. Use only in high risk cases to develop epilepsy.
- Neuroimaging: in neurologically impaired children – fever provoked convulsions
- Other investigations depend on the presentation of the child
- Treatment
- Antipyretics
- These do not reduce risk of recurrence but increases comfort
- For convulsions > 5 minutes
- Intranasal midazolam
- Rectal diazepam
- Prophylaxis
- Intermittent prophylaxis with clobazam
- Continuous AED prophylaxis with valproate or phenobarbitone
- Antipyretics
- Complications
- Todd’s paresis
- Febrile status epilepticus
- Recurrent febrile convulsions. The risk factors for recurrence include:
- Epilepsy. The risk factors for future epilepsy include:
- Simple febrile seizure (1%, like the general population)
- Recurrent febrile seizures (4%)
- Complex febrile seizure > 15 min in duration or recurrent within 24 hours (6%)
- Fever < 1 hour before feibrle seizure (11%)
- Family history of epilepsy (18%)
- Focal complex febrile seizure (29%)
- Neurodevelopmental abnormalities (33%)