Distribution of febrile seizure duration and associations with development

Abstract

Objectives-In prior studies of febrile seizures (FS), prolonged FS are defined, absent empirical evidence, as lasting 10 or 15 minutes or more. We assessed the distribution of FS duration in a cohort with first FS, and the association between FS duration and baseline characteristics of the children.Methods-We calculated the observed cumulative probability, S(t), that a FS would last at least t minutes, S(t) = exp(−t/ τ) . Data were also fit using a model obtained as the sum of two exponential distributions [S(t) = αexp(−t/τ 1 )+(1-α)exp(−t/τ 2 )]. After assessing the best fit, the cut off defining long FS was determined. Logisitic regression was used to examine associations between long FS and baseline characteristics, behavior and development.Results-In 158 children with a first FS, median duration was 4.0 minutes. Duration of FS was best fit by a two-component mixture exponential model. Using this model we identified one population that accounts for 82.3% of FS and has a mean duration of 3.8 minutes (short FS) and a second population that accounts for 17.7% of FS and has a mean duration of 39.8 minutes (long FS). Long FS were significantly associated with developmental delay (p=0.010) and delays and younger age at first FS (p=0.048).Interpretation-Like the distribution of afebrile seizure duration in children, the distribution of first FS duration is best modeled by assuming two populations. Developmental delay and younger age are associated with prolonged FS. Our data lend further support to defining 10 minutes as the upper limit for a simple FS. Febrile seizures (FS) are common, affecting 2-5% of children by 6 years of age 1 2 and are associated with an increased risk of subsequent epilepsy. Epilepsy develops in 2-4% of children with a history of FS, four times more frequently than in children without and the risk is as great as 57% in children with focal, prolonged and recurrent FS 3. In prior studies, prolonged FS have been defined in the absence of empirical evidence as those lasting either 10 minutes or more or as those lasting 15 minutes or more.1 2 4 -11 In children with first afebrile seizures, seizure duration is best fit as the sum of two exponential distributions with seizures lasting a mean of 3.6 minutes occurring in 76% of children and those lasting a mean of 31 minutes occurring in 24% of children 12. Similar information does not exist for first FS. KeywordsUsing similar methodology to that reported by Shinnar et al in afebrile seizures 12, we analyzed the distribution of FS duration in a cohort presenting with a first FS. Additionally, we determined whether the distribution of FS duration differs from what was previously reported for first afebrile seizures in children, and the association between febrile seizure duration and baseline characteristics of the children. Methods Study SubjectsIn this prospective cohort study 13, we identified children, aged 6 months to 5 years, with first FS by daily screening of the The Morgan Stanley Children's Hospital of New YorkPresbyterian Pediatric ...

Status Epilepticus

“…In this new definition, there are two time points for SE, T1, and T2. T1, which is when treatment should be initiated, is 5 min for convulsive SE based on studies that showed a seizure lasting 5 min is likely to be prolonged (Shinnar et al 2001a;Hesdorffer et al 2011). In contrast, T2, which is defined as the time point at which long-term consequences may occur, continues to be 30 min.…”

“…These prolonged febrile seizures constitute 5% -9% of all febrile seizures (Berg and Shinnar 1996;Hesdorffer et al 2011) and account for two-thirds of SE in the second year of life (Shinnar et al 1997). They are associated with essentially no mortality or detectable short-term morbidity (Maytal and Shinnar 1990;Shinnar et al 2001b).…”

Turning up the Heat on the Impact of Febrile Status Epilepticus

“…Shinnar and his multicenter FEBSTAT team report the increased likelihood of finding 1.5 Tesla MRI abnormalities generally within 1 week of the FSE episode. A large number-191 children-had imaging and were compared to a control group of 96 children with simple febrile seizures from the previously reported Columbia Febrile Seizure Study (4). The key findings were 1) 22/191 (11.5%) with FSE had T2 hyperintensities in the hippocampus versus 0% of the simple febrile seizure cohort and, 2) 20/191 (10.5%) with FSE had developmental abnormalities identified (often hippocampal malrotation) versus 2/96 (2.1%).…”

First line management of prolonged convulsive seizures in children and adults: good practice points

“…The risk of a long-lasting seizure or status epilepticus (with considerable morbidity and mortality) is very significant whenever a convulsive seizure lasts for more than 5-10 minutes [6,7]. Recent studies have elucidated a mechanism possibly underlying this phenomenon.…”