A methodological perspective on the cognitive outcome of epilepsy surgery in children and adolescents

The purpose of the study was to explore the impact of timing and test specificity of cognitive outcome measures after pediatric epilepsy surgery.

A consecutive national cohort of 114 children with medically resistant epilepsy having had resective epilepsy surgery were screened for children tested with a complete age-appropriate Wechsler Intelligence test at two or three time-points. This provided 43 children for analyses. Composite subscale scores were assessed in comparison to index and intelligence quotient (IQ) scores.

We found a main effect of time in seizure-free children for full-scale IQ (FSIQ); F(2, 42) = 6.49 with higher T2 measures compared with T1 (M_Diff = 5.46, p = .006). There was a difference in FSIQ scores between seizure-free and nonseizure-free children at T2; M = 7.31, 95% confidence interval (CI) [0.05 to 14.57], t(38) = 2.04, p = .049, favoring seizure-free children. A statistical difference between composite scale scores and index scores was found with medium to large effect. The correlation of medical treatment (anti-epileptic drug (AED)) change and score differences in FSIQ outcome was significant (p = .041), with less AED correlated with a higher FSIQ. All children with left-temporal surgery had a stable or improved verbal comprehension composite subscale score outcome at T2 regardless of seizure status.

Our results correspond to some longitudinal studies with outcome measures >2 years, in contrast to short-term studies ≤2 years with a stable outcome. Our study supports the fact that the specificity of the used tests and the timing of assessments after pediatric epilepsy surgery are essential factors for the clinical validity of outcome measures. However, there are further needs of extensive longitudinal studies to provide a better understanding of life-long cognitive development and impact after childhood epilepsy surgery.