Abstracts

Rationale: The Wechsler Intelligence Scale for Children - 4th Edition (WISC-IV) sees widespread use in children with epilepsy. However, despite numerous studies on IQ in childhood epilepsy, most used previous editions of the test and none provide information on the sensitivity of specific WISC scores (FSIQ, index and subtest scores) to epilepsy-related cognitive impairment. The goal of this study was to determine WISC-IV index and subscale strengths and weaknesses in children with epilepsy and define the relationship between WISC-IV scales, demographic factors and epilepsy variables. Methods: Retrospective data from clinically-referred children between ages 6 and 16 were recruited at the Alberta Children s Hospital and the New York University Comprehensive Epilepsy Center. All received a neuropsychological assessment that included the WISC-IV. Results: WISC-IV scores were available for 106 children (46 girls, 60 boys; mean age = 11.0, SD = 3.1) with mean maternal education of 14.6 years (SD = 3.04). Of the sample, 69.4% were Caucasian, 76% were right handed, 54% had a positive MRI, and 44 had a clearly lateralized focus on EEG involving either the right (18) or left hemisphere (26). Most had early-onset epilepsy, were on multiple AEDs, and had high seizure burden. There were no significant differences between sites on demographic, epilepsy variables or FSIQ. The mean FSIQ was low average (M = 80.07, SD = 22.60) as were the means for the WISC-IV index scores, and 35.8% of children had FSIQ < 70. Mean Verbal Comprehension Index (VCI) was significantly lower than Perceptual Reasoning Index (PSI; p = .01), and PRI was greater than Working Memory Index (WMI) and Processing Speed Index (PSI; p = .01, p < .0001, p < .0001, respectively). No other differences between index scores were found. At the subtest level, mean scores were highest on the Matrix Reasoning (M = 8.12, SD = 3.73) and lowest on Coding (M = 5.87, SD = 3.60). In terms of percent of children on each subtest with low scores (i.e., scores below 2SDs from the expected normative mean of 10), Coding identified the most children (28.3%) with low scores, and Similarities identified the fewest (11.3%). Later age at onset and shorter epilepsy duration were both correlated with higher WISC-IV FSIQ and index scores (rs ranging from .36 to .45, p <.0001), and number of current and previous AEDs were inversely correlated with FSIQ and index scores (rs = -.25 to -.46, all ps < .0001). Neither the FSIQ or index scores were related to seizure frequency. A similar pattern was found for subtest scores. No differences in FSIQ, index scores or subtest scores were found between children with left and right seizure foci, or between MRI-positive and MRI-negative children. Conclusions: The WISC-IV is sensitive to epilepsy-related cognitive impairment in children, particularly those relating to expressive verbal, working memory and processing speed. Although WISC-IV scores are related to markers of epilepsy severity such as age at onset, the test should not be used for inferring seizure laterality.