Febrile Convulsions

Introduction

A febrile convulsion is a seizure occurring in a young child in association with fever, in the absence of intracranial infection, metabolic disturbance or a history of afebrile seizures. It is defined by exclusion, which is precisely why the clinical assessment matters even though the outcome is almost always benign.¹

Between 2% and 5% of children have at least one, most commonly between 12 and 18 months of age. For the family it is often the most frightening experience of their lives - a substantial proportion of parents believe their child is dying while it is happening - and the quality of the explanation they receive afterwards determines how they cope with the next febrile illness.

The clinical task has three parts: manage the seizure itself, exclude the diagnoses a febrile convulsion can be mistaken for, and counsel the family properly. Students reliably remember the first and neglect the third, which in an OSCE is where most of the marks sit.

Pathophysiology

The immature brain is inherently more excitable than the mature one. Excitatory glutamatergic transmission develops before inhibitory GABAergic transmission matures, and in the first years of life GABA is at times depolarising rather than hyperpolarising. This gives a narrow window - roughly 6 months to 6 years - during which fever can lower the seizure threshold enough to provoke a convulsion in an otherwise normal brain.

Fever contributes in several ways. Pyrogenic cytokines, particularly interleukin-1 beta, directly increase neuronal excitability; the respiratory alkalosis produced by fever-driven hyperventilation lowers the seizure threshold further; and raised temperature alters the kinetics of temperature-sensitive ion channels.

There is a clear genetic contribution. A family history of febrile convulsions is present in 25-40% of cases, and inheritance in some families follows an autosomal dominant pattern. Mutations in sodium channel subunits SCN1A and SCN1B and in the GABA receptor subunit GABRG2 underlie the syndrome of genetic epilepsy with febrile seizures plus (GEFS+), in which febrile seizures continue beyond the usual age or are accompanied by afebrile seizures.

It is the rate of rise of temperature that appears to matter more than the peak, which is one reason antipyretics given once the fever is established do not prevent a seizure - and why the convulsion is so often the very first sign that the child is unwell at all. Human herpesvirus 6, the cause of roseola infantum, and influenza A are the viruses most frequently identified.

Classification

Febrile status epilepticus describes a febrile seizure lasting 30 minutes or more, or repeated seizures without recovery of consciousness over that period. It accounts for around 5% of febrile convulsions and is the subgroup with the greatest association with later temporal lobe epilepsy.

Clinical assessment

By the time you see the child the seizure has usually stopped. The history is therefore the investigation, and it should establish exactly what happened and, more importantly, what else might explain it.

History

• A detailed description of the event from someone who saw it - what the child was doing, whether it started on one side, whether the eyes deviated, the colour, the duration, and how long recovery took. Duration is almost always overestimated, so ask about landmarks rather than minutes.
• The febrile illness - how long the child has been unwell, and any localising symptoms
• Immunisation status and any recent vaccination
• Recent antibiotics, which can partially treat and mask meningitis
• Past history of seizures, febrile or afebrile, and any developmental concerns
• Family history of febrile convulsions or epilepsy
• Travel, contacts and any possibility of ingestion of medication or another toxin

Examination

• Full observations and a formal assessment against the NICE traffic light system²
• Conscious level, which should be steadily improving. Persistent drowsiness beyond an hour is not a post-ictal state and needs explaining.
• Search for the source of fever - ears, throat, chest, abdomen, joints and skin
• Meningism - neck stiffness, bulging fontanelle, photophobia. These are unreliable in infants, where irritability, an abnormal cry and poor feeding may be the only signs.
• Whole-body skin inspection with the child undressed, specifically for a non-blanching rash
• Focal neurological signs, including Todd's paresis, and a fundoscopy where feasible
• Capillary blood glucose in every child who has had a seizure - this is not optional

Differential diagnosis

• Bacterial meningitis or encephalitis - the diagnosis that must not be missed, and the reason for the whole assessment⁴
• Rigors - shivering with fever, which can look convulsive but has no loss of consciousness and stops if the limb is held
• Reflex anoxic seizure - triggered by a sudden unpleasant stimulus, with pallor, brief asystole and a short tonic episode
• Breath-holding attack - preceded by crying, with cyanosis and then loss of consciousness
• Syncope with secondary anoxic jerks - more common in older children
• Metabolic causes - hypoglycaemia, hyponatraemia and hypocalcaemia, all of which can coexist with a febrile illness
• Epilepsy with fever-provoked seizures - a child with an existing seizure disorder in whom fever simply lowers the threshold
• Dravet syndrome - prolonged or hemiclonic seizures with fever starting in the first year, then afebrile seizures and developmental regression, usually from an SCN1A mutation
• Intracranial haemorrhage or non-accidental injury, and drug or toxin ingestion

Investigations

A child with a simple febrile convulsion, an identified source of fever and complete recovery needs no neurological investigation at all. Investigation is directed at finding and treating the cause of the fever.

• Capillary blood glucose - in every child after a seizure
• Urine dipstick and culture - urinary tract infection is a common occult source, particularly in infants²
• Bloods (FBC, CRP, U&Es, cultures) - only if the child is systemically unwell, has no identified source, or falls into the amber or red NICE categories. They are not routine in an uncomplicated case.
• Chest radiograph - only if there are respiratory signs
• EEG - not indicated after a simple febrile convulsion. It does not predict recurrence or later epilepsy, and abnormal findings in this setting lead to unnecessary anxiety and treatment.⁷
• Neuroimaging - not routine. Reserved for focal neurological deficit persisting after the seizure, suspected raised intracranial pressure, a known neurological abnormality, or suspected head injury.

Lumbar puncture

The decision on lumbar puncture is the most examinable point in this topic. It is not performed routinely, but the threshold is deliberately low in the situations where meningitis is hardest to detect clinically.

• Perform if there are any clinical signs or symptoms of meningitis or encephalitis
• Perform, or have a very low threshold, in an infant under 12 months, in whom meningeal signs are unreliable - and particularly under 6 months, where the diagnosis of febrile convulsion should not really be made at all
• Perform if the child is already taking antibiotics, which can mask meningitis
• Consider after a complex febrile convulsion, or where recovery is incomplete or consciousness remains altered
• Do not perform if there is cardiorespiratory instability, signs of raised intracranial pressure, focal neurology, a coagulopathy or a low platelet count, or local infection at the site - give antibiotics first and defer the procedure

Management

During the seizure

1. Note the time. Duration determines everything that follows.
2. Protect the child from injury - move furniture away, place something soft under the head, and do not restrain them or put anything in the mouth
3. Airway, breathing, circulation - once the convulsion stops, place the child in the recovery position and give high-flow oxygen if saturations are low
4. Check the blood glucose and treat hypoglycaemia immediately
5. If the seizure lasts more than 5 minutes, give a benzodiazepine: buccal midazolam is first line in the community and in hospital, with rectal diazepam as an alternative where midazolam is unavailable⁶
6. A second dose after a further 10 minutes if the seizure continues, at which point senior help and the status epilepticus pathway are needed - typically intravenous levetiracetam or phenytoin, and then rapid sequence induction if these fail⁵
7. Treat the cause of the fever, and give antipyretics if the child is distressed

Admission

Not every child needs admitting, but the threshold is low, particularly for a first event.

• Admit any child with a first febrile convulsion, any complex features, or no identified source of fever
• Admit children under 18 months, in whom assessment is harder and serious infection more likely
• Admit if the child remains drowsy, is systemically unwell, is on antibiotics, or falls into the NICE amber or red categories
• Admit where the family cannot cope or cannot return easily - parental distress after a first seizure is a legitimate reason
• Discharge may be reasonable after a recurrent simple febrile convulsion in a child over 18 months who has fully recovered, has an obvious viral source, and whose parents have been counselled and given clear written advice

Preventive treatment

• Antipyretics do not prevent febrile convulsions. Paracetamol and ibuprofen are given for the child's comfort, and this should be stated explicitly rather than left ambiguous - parents commonly believe otherwise and blame themselves for missing a dose.¹
• Regular antiepileptic drugs are not recommended. The adverse effects outweigh any benefit in a condition with such a good prognosis.
• Rescue medication - a supply of buccal midazolam with a written protocol is provided for children who have had prolonged seizures, live far from medical help, or have frequent recurrences
• No restriction on immunisation. Vaccines may provoke a febrile convulsion, but this is not a contraindication to continuing the schedule - advise antipyretics for comfort and continue as normal.

Prognosis

Recurrence

Around 30-35% of children have at least one further febrile convulsion, and about 10% have three or more. Most recurrences happen within a year of the first. The risk is higher with:

• Age under 18 months at the first seizure - the single strongest predictor
• A family history of febrile convulsions
• A relatively low temperature at the time of the seizure
• A short interval between the onset of fever and the seizure, typically under an hour
• Attendance at nursery, simply through more frequent febrile illnesses

Risk of epilepsy

Prolonged febrile status epilepticus is associated with later mesial temporal sclerosis and temporal lobe epilepsy. Whether the prolonged seizure causes the hippocampal injury or simply reveals a brain that was already abnormal remains unresolved, and the honest answer to a parent is that the association exists but that the absolute risk after a single prolonged seizure remains low.³

Otherwise the outlook is genuinely excellent. Febrile convulsions do not cause brain damage, and there is no measurable effect on intelligence, behaviour, school performance or mortality. Children grow out of them, typically by the age of 5 or 6.

Given how benign this is, the most valuable thing a clinician does is explain it well: name the condition, say clearly that it is common and not dangerous, correct the antipyretic myth, describe exactly what to do next time, and provide written information. A family that leaves understanding those five things will manage the next episode far better than one that leaves with a prescription and no explanation.