Abstracts

RATIONALE: The study was conducted to test the common assumption that a discrepancy between the Verbal IQ (VIQ) and Performance IQ (PIQ) provides accurate information for lateralization of seizure focus in pre-surgical evaluations.
METHODS: Results of the Wechsler Intelligence Scale for Children - III from patients treated with focal surgical resection between 1994 and present were reviewed. The resulting sample characteristics are as follows: Mean age at test = 12.41; Mean age at seizure onset = 5.29; Gender = 48% male; Side of focus = 59% left; Lobe of surgical resection - 26% frontal, 52% temporal, 21% parietal/occipital. Difference scores were calculated by subtraction of PIQ from VIQ and Perceptional Organization Index (PO) from Verbal Comprehension Index (VC). An absolute difference of 15 points was defined as a significant discrepancy. A lateralization accuracy score was calculated by comparing IQ -based prediction to confirmed side of seizure focus.
RESULTS: VIQ/PIQ discrepancies were found in 39% of the sample, while VC/PO discrepancies were found in 33% of the sample. Regression analysis showed no relationship between magnitude of discrepancy and the age at testing or age at seizure onset. Predicted side of dysfunction was unrelated to the actual side of seizure focus or to the presence of abnormality on MRI scan. VC/PO discrepancies were more likely to be found in males (Chi Square = 5.80, df = 1, P[lt].016). VIQ/PIQ discrepancies were not significantly related to gender. Of the discrepancies identified, patients with frontal or parietal seizure foci only demonstrated discrepancies indicating right hemisphere dysfunction, while temporal lobe patients demonstrated an equal number of discrepancies implicating the right and the left hemisphere. Accuracy of prediction was unrelated to side or lobe of seizure focus. For 72% of the sample, follow up data regarding the effectiveness of surgery in producing seizure control was available. There was no relationship between the accuracy of prediction or IQ-based evidence of lateralized dysfunction and surgical outcome.
CONCLUSIONS: Results indicate that the VIQ/PIQ split and the VC/PO split are not accurate indicators of laterality of brain dysfunction in pediatric epilepsy patients. The failure to find more frequent accurate lateralizing information in IQ test performance may reflect the degree of plasticity in the young brain. It is also possible that focal epileptiform activity may have a global rather than focal effect on brain development. The higher incidence of VIQ [gt] PIQ findings may reflect the fact that PIQ measures are timed and therefore more likely to be affected by sedating effects of medication. Results support the need for use of a comprehensive neuropsychological battery, going beyond IQ testing in pre-surgical evaluation of patients.