New research published in The Lancet finds that childhood seizures due to fever – febrile seizure – do not increase long-term mortality. During the two years following complex febrile seizures, there appears to be a doubling of mortality, but the overall risk of death associated with febrile seizures remains extremely low. Dr Mogens Vestergaard (Department of General Practice, Institute of Public Health, Aarhus University, Denmark) and colleagues want to reassure parents that even in high-risk children, death after febrile seizure is very rare.
Febrile seizure (also known as fever fit) is a generalized convulsion caused by elevated body temperature. About two to five percent of children under five years old are affected by febrile seizure, and about 33% of these have more than one episode. Often, parents who witness their child seize, whether it be the first or subsequent episode, believe that their child is dying. It is known that underlying neurological disorders are a cause of excess mortality in children with epilepsy, but little is known about how febrile seizures in children affect mortality. This led Danish researchers to study a large cohort of children in Denmark, analyzing mortality after febrile seizures with up to 28 years of follow-up.
The researchers studied 1,675,643 children born in Denmark between 1977 and 2004. Children were followed up from 3 months old until they died, emigrated, or August 31, 2005. Of the sample, 8,172 children eventually died, including 232 of 55,215 children who had a history of febrile seizure. The researchers found that 132 per 100,000 children died during the two year period after a febrile seizure, and 67 per 100,000 died who did not have a history of the condition.
A simple febrile seizure is characterized by lasting less than 15 minutes and not recurring within 24 hours, whereas a complex febrile seizure lasts more than 15 minutes and/or recurs within 24 hours. Children who had simple febrile seizures had mortality rates similar to the general population. However, children who had more complex febrile seizures had a two-times greater mortality rate during the two years following the episode than the general population. After the two years, mortality rates stabilized to the rate in the general population. Although this is a doubling of risk, note the authors, the absolute risk is still small. For example, in children followed up for two years, the general population would see one death in 1500 children and those with a history of febrile seizure would see two deaths in 1500 children.
“Children with simple febrile seizures had a risk of death similar to the background population, whereas those with complex febrile seizures, febrile seizures triggered by temperature below 39°C, and febrile seizures occurring before 12 months of age had a two-fold higher mortality lasting for about two years. The excess mortality was at least partly due to pre-existing neurological abnormalities and subsequent epilepsy…Parents should be reassured that death after febrile seizures is very rare, even in high-risk children,” conclude the authors.
Dr Maitreyi Mazumdar (Department of Neurology, Children’s Hospital, Boston, MA, USA) adds in an accompanying comment that: “Vestergaard and colleagues’ study again seems to refute, for infants and children who have simple febrile seizures, the idea of a shared cause between febrile seizures and sudden death…[the] study suggests that there is a subset of children with febrile seizures – notably those with complex features and underlying neurological abnormalities – that may warrant closer attention and follow-up.”
Death in children with febrile seizures: a population-based cohort study
M Vestergaard et al.
The Lancet (2008). 372(9637): pp. 457 – 463.
Written by: Peter M Crosta