Febrile Seizures

Background

Introduction

Febrile seizures are a type of benign seizure that occurs during a febrile episode in infants and children 3 months to 5 years of age. A true febrile seizure is a normal physiologic response to abnormal brain electrical activity caused by a fever. The pathophysiology is unknown but a family history may suggest genetic susceptibility. Febrile seizures do not represent brain abnormalities, perhaps only a lower seizure threshold, and carry excellent long-term prognoses.

Statistics

febrile seizures occur in 2-4% of infants and children under 5 years of age, with the majority between 12-18 months of age
up to 50% of cases will show recurrence if the first febrile seizure occurred when under 1 year of age
75% recur within 12 months of the first febrile seizure
risk increases with a family history of febrile seizures
risk factors for developing afebrile seizures after first febrile seizure include:
- Developmental or neurologic abnormalities prior to the febrile seizure
- Atypical first febrile seizure
- Family history of afebrile seizures
Outside of the 3mth-5yr age group, febrile seizures are uncommon and other etiologies (link to other seizure section) must be ruled out.

Diagnosis

Criteria

Generally accepted criteria of a febrile seizure are seizure activity in the context of:

A temperature greater than 38ºC (seizures often occur during a rapid increase in temperature)
An infant or child between 3 months and 5 years of age
No CNS infection or inflammation
No acute systemic metabolic abnormality that may produce convulsions
No history of afebrile seizures.

Clinical categories

Febrile seizures are clinically categorized as being simple or complex:

	SIMPLE / TYPICAL	COMPLEX / ATYPICAL
DESCRIPTION	Generalized: clonic or tonic-clonic	Focal neurological symptoms (pop-up 1) : pre, during, post-seizure
DURATION	< 15 min	> 15 min
FREQUENCY	Only 1 per 24 h	>1 per 24 h
PROPORTION OF FEBRILE SEIZURES	75%	25%
RECURRENCE RISK (a,b,c)	30-50%	30-50%
RISK OF FUTURE AFEBRILE SEIZURES	~2% (vs 1% in general population)	2-50% (d)

Questions to ask

It is important to realize that seizures are a symptom of abnormal brain activity, not a disease in itself, thus your history should focus on ruling out any possible pathologic cause of the seizure.

Was it really a seizure? If yes, what type – typical or atypical?

Ask a witness to describe the child’s activity, specifically ask about

decreased awareness or loss of consciousness
response to stimulus during the episode
post-ictal confusion/fatigue.

Ask for a description of the motor activity and how it progressed

focal (pop-up 1): aura, localized movements or paralysis, post-ictal neurologic deficit
generalized: whole body stiffness or shaking

Ask about other details suggestive of an atypical seizure as outlined above.

What is the source of the fever? In particular, Is this meningitis or another intracranial infection?

Ask if there has been any recent illness or recent immunizations. The risk of febrile seizures is increased on the day of DTP vaccination and 8 to 14 days following MMR vaccination

Ask about symptoms suggestive of meningitis (pop-up 3) or increased intracranial pressure (link to Signs of inc_ICP.doc) due to other CNS infections (encephalitis, brain abscess)

Ask about other non-febrile causes of the seizure. For example, electrolyte abnormalities due to persistent vomiting with a current viral illness. In past medical history, ask about neonatal history, head trauma, developmental delays, previous neurological deficits, current medical conditions, personal and family history of seizures, and any medications that may lower the seizure threshold.

Physical examination

The main purpose of the physical exam and any further investigations is to determine neurological status, identify the source of infection, and rule out CNS infection.

A full physical exam is performed to identify any focus of infection, such as the ears, upper respiratory tract, lungs, skin, GI tract, or urinary tract. The neurologic and developmental examination should be normal in an otherwise healthy infant or child.

Meningitis (pop-up 3) and intracranial infection may be suggested on physical exam by altered level of consciousness, lethargy or irritability, hypotension, signs of increased intracranial pressure (link to Signs of inc_ICP.doc), petechial rash, nuchal rigidity or positive Kernig’s or Brudzinski’s signs (link to kernig.brudzinski.doc).

Investigations

Special investigations, in particular lumbar puncture, blood studies, CNS imaging and EEG, are primarily used to rule out CNS infection. The American Academy of Pediatrics has made several recommendations outlined below for investigations of the first presentation of typical/simple seizures with a fever in an otherwise healthy child or infant. However, these are only recommendations and you need to consider the entire clinical context, including the presence of any atypical febrile seizure features, to decide which, if any, special investigations are warranted.

Lumbar puncture (LP)

This should be strongly considered in an infant under 12 months of age, as the signs and symptoms of meningitis may not be present regardless of infection. Between 12-18 months of age, an LP should be considered as symptoms of meningitis may not be obvious. In a child over 18 months, LP is not routinely recommended, unless history, signs and symptoms suggest of meningitis or intracranial infection.

Blood Studies

Blood studies, including electrolytes, calcium, phosphorus, magnesium, CBC and blood glucose, are not routinely recommended. CBC may be of use in evaluating an infection, blood glucose with prolonged obtundation, or electrolytes with persistent vomiting secondary to the infection.

EEG

EEG studies are not routinely recommended. Although EEG changes can be present post simple febrile seizure, these are not indicative of any long term morbidity or development of epilepsy.

CNS Imaging:

Imaging is not recommended for the first presentation of a simple febrile seizure.

Management

The goals of management are:

To prevent injury

During the seizure any surrounding hazards or objects in the patient’s mouth should be removed to prevent secondary injury. Anti-pyretics will not reduce the risk of future febrile seizures, however they may still be useful for improving the comfort of the child. In terms of long-term prevention, neither continuous nor intermittent anti-convulsant therapy has been shown to reduce the recurrence of simple febrile seizures, thus are not recommended. Rectal valium at a dose of 0.5mg/kg (max 10 mg) may be given to help terminate seizures lasting > 5 minutes

To reassure and educate the family

Reassurance and education should focus on
- the benign nature of the seizure
- the risk of another febrile seizure
- the risk of future afebrile seizures/epilepsy
- how and when to administer rectal valium
- safety during a seizure and when to call an ambulance

Acknowledgements

Written by: Nancy Martin

Edited by: Elmine Statham