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FEBRILE SEIZURES

DEFINITION:

A benign seizure occurring in the absence of evidence of meningitis or encephalitis in a febrile child.

EPIDEMIOLOGY:

incidence: 2-5% of febrile children less than 5 years of age
- 40% of all first seizures are febrile
- most common seizure disorder in childhood
age of onset:
- between 4 months -> 5 years
- peak (14-18 months); median (18 months)
risk factors:
- temperature >38 C
- having 2 or more of the following increase the risk of having a febrile seizure from 2-5% to 30% in the general population:
  - a first degree relative (parent or sibling) with a febrile seizure
  - a second degree relative (uncle, aunt, grandparent) with a febrile seizure
  - developmental delay (slowed psychomotor development)
  - delayed neonatal discharge (of >28 days)
  - attendance at day care

PATHOGENESIS:

1. Background

positive family history of febrile seizures may indicate a predisposition towards a lowered seizure threshold in these patients
there is little clinical evidence that the rate of temperature rise is what provokes a febrile seizure

CLINICAL FEATURES:

1. Simple Febrile Seizures

1. Definition

a primary generalized seizure lasting less than 15 minutes and not recurring within 24 hours

2. Postictal Period

paralysis of one limb or a gaze palsy (Todd's paralysis) may be noted in the immediate postictal period
drowsiness
neurologically normal before and after seizure
no increased mortality, hemiplegia, or mental retardation

2. Complex Febrile Seizures

1. Definition

a seizure which is focal, prolonged (>15 minutes), and/or recurring within 24 hours of the initial seizure
focal seizures may involve an arm, leg, or face on one side only or eye deviation towards one side

INVESTIGATIONS:

1. Routine Blood Work

CBC with differential
electrolytes:
- a serum sodium between 136-142 mmol/L (normal range) is associated with a recurrence risk of 10%
- a serum sodium less than 130 mmol/L is associated with a recurrence risk of 60%
others:
- magnesium, calcium, phosphorous, and glucose are not indicated on a routine basis

2. Septic Work-up

if clinically indicated
to rule out sepsis or meningitis
- CBC with diff.
- urinalysis
- blood cultures
- lumbar puncture
- chest x-ray
as the signs and symptoms of meningitis may be minimal or absent in those less than 18 months of age, a lumbar puncture should be considered in those patients less than 18 months of age

3. CT/MRI

not indicated even for multiple complex febrile seizures

4. EEG

not indicated even for multiple complex febrile seizures

MANAGEMENT:

1. Acute

1. Control Temperature

tylenol 15 mg/kg/dose po q3-4h
sponging a febrile child with tepid water does not appear to be effective in reducing an elevated temperature

2. Control Seizure

rectal valium or ativan are the drugs of choice for acute prolonged febrile seizures
diazepam (valium) 0.3-0.5 mg/kg PR or
lorazepam (ativan) 0.05-0.1 mg/kg PR

2. Prophylaxis

1. Intermittent

medications to be used whenever the temperature >38 C
intermittent anticonvulsant therapy with diazepam may prevent recurrences but is associated with side effects (ataxia, lethargy, irritability)

2. Prolonged

medications given on a daily basis
prolonged anticonvulsant therapy with phenobarbitol, valproic acid, phenytoin, or carbamazepine for prevention of recurrences is not indicated

3. Prognosis

1. Recurrence Risk

there is a 30-40% chance of at least one recurrence and a 10% chance of three or more recurrences
most recurrences occur within 6-12 months of the initial febrile seizure
risk factors for recurrence:
- family history of febrile seizures and/or epilepsy
- age <14 months at first febrile seizure
- a short duration of illness (less than 24 hours) prior to the febrile seizure
- low temperature at time of the febrile seizure
- attendance at day care
- developmental delay
- (complex febrile seizures do not appear to be a risk factor for recurrence)

2. Epilepsy Risk

only 2-4% of children with one febrile seizure develop epilepsy (i.e., 96-98% don't)
- only 2% of children with a simple febrile seizure develop epilepsy
- 12% of children with a complex febrile seizure develop epilepsy
15-20% of children with epilepsy have a history of a previous febrile seizure (this may indicate that febrile seizures act as a marker for those with a lower seizure threshold)
there does not appear to be any significant risk factors to indicate those who will develop epilepsy after a single febrile seizure

3. Brain Damage

there does not appear to be any evidence that a prolonged febrile seizure (greater than 15 minutes) causes subsequent brain damage (however, any child seizing for an hour or more may be at risk)

ADDITIONAL REFERENCES:

1. Camfield, P.R. and C.S. Camfield; Management and Treatment of Febrile Seizures; Curr. Probl. Pediatr. 27:6-13, (1997).

2. Camfield, P.R. and C.S. Camfield; Febrile Seizures: Ten Common Misconceptions; Paediatr. Child Health 1(3):220-223, (1996).

3. Hilliard, R.; Febrile Seizures; Paediatr. Child Health 1(3):225-226, (1996).

4. Provisional Committee on Quality Improvement, Subcommittee on Febrile Seizures; Practice Parameters: The Neurodiagnostic Evaluation of the Child With a First Simple Febrile Seizure; Pediatrics 97(5):769-771, (1996).

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