Abstracts

Rationale: It is well known that epilepsy has a negative impact on a child s intellectual development. Cormack and colleagues (2007) reported that intractable epilepsy can result in at least a 1-2 standard deviation difference in mean intelligence compared to healthy children. Although determining strengths and weaknesses in relation to healthy peers is important, it is also valuable for clinicians to be able to determine whether a child s cognitive abilities are similar to, above, or below the level expected for patients with refractory epilepsy. The purpose of this study is to present clinical normative data for WISC-IV performance in American and Canadian patients with refractory epilepsy. Methods: Participants included consecutively referred children and adolescents between the ages of 6-16 years with medically-determined refractory epilepsy from the New York Comprehensive Epilepsy Centre (American sample, n=50) and the Calgary Epilepsy Programme in Calgary, Canada (Canadian sample, n=76). All participants were administered the Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV; Wechsler, 2003) as part of their clinical work-up. Results: American participants had a mean age of epilepsy onset of 4.9 years (SD=4.3; range=0-14.3 years), mean duration of epilepsy of 6.0 years (SD=4.0; range=0.1-15.4 years), and a mean number of previous antiepileptic medications of 2.1 (SD=2.1; range=0-10). The mean age at assessment for the American sample was 10.9 years (SD=3.3; range=6.5-16.3 years). Canadian participants had a mean age of epilepsy onset of 5.2 years (SD=4.1; range=0-16 years), mean duration of epilepsy of 5.9 years (SD=4.0; range=0.2-14.2 years), and a mean number of previous antiepileptic medications of 2.1 (SD=2.5; range=0-9). The mean age at assessment for the Canadian participants was 11.2 years (SD=2.8; range=6.2-16.4 years). Overall, there are no appreciable differences between the American and Canadian samples for the variables used to determine the severity of epilepsy. American participants had a mean WISC-IV full scale IQ score of 82.8 (SD=24.1; range=41-132). Nearly one-third of the sample had full scale IQ scores that were below the 2nd percentile (i.e., full scale IQ<70). Clinical norms for full scale IQ in the American sample suggest that it is average for children with epilepsy to have full scale IQ scores between 63 and 101. Canadian participants had a mean WISC-IVCDN full scale IQ of 75.0 (SD=18.7; range=40-109). Having a full scale IQ score below the 2nd percentile was found in 38% of the Canadian sample. Clinical norms for full scale IQ in the Calgary sample suggest that it is average for children with epilepsy to have full scale IQ scores between 59 and 92. Conclusions: Epilepsy can have a deleterious effect on intellectual growth and development. However, there is considerable value in knowing whether the impact on intelligence in any given patient is consistent with the known effects of epilepsy on intelligence. The information presented in this study will be useful for any clinician who evaluates a child or adolescent with severe epilepsy.