Convulsive Status Epilepticus Has Prolonged Cognitive Effect

Pauline Anderson

April 10, 2013

Compared with healthy infants, those who experience prolonged febrile seizures (PFSs) have decreased cognitive and language function early on, as do children with nonfebrile convulsive status epilepticus (CSE), and these lags continue at 1 year, a new study has found.

The results suggest that the developmental effects of these seizures aren't transient, said the study authors, led by Marina M. Martinos, PhD, Developmental Cognitive Neurosciences Unit, UCL Institute of Child Health, London, United Kingdom.

"[T]he present data allow for the possibility that CSE may have a longer-lasting impact on future development through a more permanent reorganization of functional networks, which may have already taken place when we first assess these children."

The study was published online April 8 in Epilepsia, a journal published by Wiley on behalf of the International League Against Epilepsy.

Theoretical Possibility

According to background information in the study, CSE is the most common pediatric neurologic emergency. Its incidence is highest within the first 3 years of life, a period of critical growth and development in children.

The current study included 54 children between 1 and 42 months of age who had at least 1 episode of CSE between December 2006 and March 2010. CSE was defined as a tonic, clonic, or tonic-clonic seizure (continuous) or 2 or more seizures without regaining consciousness (intermittent) that lasted at least 30 minutes.

The group included those with PFS, defined as CSE in an otherwise neurologically normal child with a fever (n = 27) and a nonfebrile CSE group (n = 27). The 5 categories of CSE were acute symptomatic, remote symptomatic, idiopathic epilepsy related, cryptogenic epilepsy related, and unclassified.

The 2 groups were similar in seizure characteristics, including age at CSE, duration of and time from seizure, proportion of generalized vs focal onset, and proportion of continuous vs intermittent CSE. These patients underwent MRI and neuropsychological assessments at baseline (a mean of 38 days after CSE) and a year later.

The analysis also included control group of 17 healthy, normally developing children (mean age, 20.49 months) who were seen once during the study.

At baseline, the mean composite score on the Bayley Scales of Infant Development (third edition) showed the nonfebrile CSE group had significantly lower scores from the mean on cognitive, language, and motor scales. The PFS group had significantly lower scores from the mean on the cognitive and language scales. The controls performed above the normative mean on language measures.

At follow-up, 38 children were available for assessment: 22 had been classified as having PFS at baseline and 16 as having nonfebrile CSE. Tests revealed no difference in performance from baseline to follow-up for the PFS (cognition: P = .809; language: P = .181, motor: P = .394) and the nonfebrile CSE (cognition: P = .454; language: P = .444; motor: P = .634) groups.

Results also showed that seizure-related variables, such as duration, were not predictive of developmental outcomes.

"Taken together, these findings exclude the theoretical possibility that PFS has a transient effect on performance a few weeks onward," write the authors. "Namely, if seizure activity in itself affects outcome it does so in a more permanent fashion."

Unexpected Finding

The finding that children with PFS lagged behind controls developmentally was the most unexpected finding, note the authors. "It is important to note that these impairments are not only confined to the nonfebrile CSE cases, who are already associated with neurologic abnormalities at baseline, but are extended to the PFS cases, who perform worse than controls on the assessed measures."

The mean age of the children with PFS in the study was 18.4 months, and by definition, PFS occurs from ages 6 to 72 months. However, most PFS occurs before 43 months, which suggests that "the current findings represent most of the PFS population and are not excluding a sizeable chunk," the authors write.

The cognitive lag could be due to a brain injury caused by the PFS, or factors that predispose someone to develop PFS may also lead to reduced function. A third possibility is a cumulative effect of combined factors: a brain at risk, along with an effect of the seizure itself.

The CSE study population may not be representative of the population as a whole, they caution. A second limitation is that only 35% of the identified sample agreed to take part in the study.

The study was supported by the Wellcome Trust. The authors have disclosed no relevant financial relationships.

Epilepsia. Published online April 8, 2013. Abstract