Fever and Febrile Convulsion

Fever is not generally seen as a beneficial or desirable response.  It is more commonly seen as an adverse effect of an infective illness, to be quashed at all costs.

But fever is part of the immune system's normal reaction to acute infection and thus is a common and normal response to childhood infections.

Fever greater than 38C aids the immune response.  It kills bacteria and viruses, increases white blood cell numbers and increases white blood cell activity and movement.

Parents, understandably, tend to fear fever, particularly due to the possibility of febrile convulsions.

A febrile convulsion is defined as a ‘generalized seizure which occurs in response to a febrile stimulus in a neurologically normal child.’

• The seizure is brief, less than five minutes duration. Although it may seem much longer to a frantic parent.
• It is the commonest seizure disorder of childhood,  occurring in 2-4% of all children in U.K and U.S.
• It occurs in children between two months and five years of age, with the peak incidence at eighteen months of age.
• There is a high familial incidence, although the mode of inheritance is unknown.
• The threshold for febrile convulsion differs in individual patients and it appears that the rapidity of rise in temperature is more significant than the maximum temperature reached.
• Statistically, convulsions occur early in the illness at the first rise in temperature.

These factors are not associated with higher risk of epilepsy and only a very small number of children with febrile convulsions go on to develop epilepsy.

Research shows that viruses are the most common cause of illness in children admitted to hospital with a febrile convulsion.   A febrile convulsion is not indicative of an infection of the central nervous system and the prevalence of meningitis, either bacterial or viral is only 1-2%.

A review of seven Chicago hospitals over a two year period showed that the rate of serious bacterial infection was very low in children presenting with their first febrile convulsion.  The prognosis is generally good and children with a history of febrile convulsions are at no greater risk of intellectual impairment than their peers

Neurology.J.2001 reported a study of working memory of school children with a history of febrile convulsion.  It found that children with a history of febrile convulsion demonstrated significantly better memory, more flexible processing and higher impulsivity than their age-matched controls.  The underlying mechanism was unknown.

The rate of recurrence in children who have had febrile convulsions has been studied in 2496 children.  24% had one recurrence, 15% had two recurrences and 7% had three or more recurrences.

The rate of recurrence rapidly declines six months after the seizure.

The recurrence rate is higher if the child is under two years of age, if the temperature is relatively low at the time of the seizure and  if there is a family history of a first degree relative with febrile convulsions.

Febrile convulsions and anti-pyretics

A Netherlands study looked at children in the six months after their first febrile convulsion.  For any fever greater than 38C, they were given either an anti-pyretic (fever lowering medication) or a placebo.  There was no significant difference in rate of recurrence of febrile convulsion between the two groups.

J Clin Nursing reported that antipyretics form the basis for treatment of febrile convulsions although they are not recommended in published guidelines.  There is little evidence that prophylactic (preventative) use has any effect in reducing the incidence of febrile convulsion.  Consequently, information to reduce parental fear and education on management of the child during the convulsion, may be more efficacious.

Febrile convulsions and anti-convulsants

Two hundred studies of various anticonvulsants following a febrile convulsion showed a reduction in the incidence of recurrence with prophylactic dose.

However epidemiological studies demonstrate a very low risk of epilepsy and nil occurrence of other adverse outcomes. In other words, febrile convulsions are fairly benign.  Thus although anticonvulsants were effective, their use was not recommended because of the high incidence of significant adverse effects such as irritability, somnolence and diminished cognitive development.