Estimated IQ (EIQ) Systematically Overestimates Full-Scale IQ (FSIQ) in Survivors Irradiated for Pediatric Brain Tumors

While often essential to attain a cure for pediatric brain tumors, radiotherapy (RT) has been associated with adverse neurocognitive sequelae manifested as declines in FSIQ. In particular, processing speed is the FSIQ component most adversely affected by RT. EIQ is frequently used in both research and clinical settings in place of FSIQ. EIQ is typically calculated from Vocabulary, Information, and Block Design subtests, none of which assess processing speed. Although EIQ and FSIQ are highly correlated, we hypothesized that EIQ may systematically underestimate neurocognitive sequelae of RT in pediatric brain tumor survivors. One hundred eighty-six pediatric brain tumor (medulloblastoma, germ cell tumor, craniopharyngioma, ependymoma and others) patients were treated for proton RT at one institution. All patients had a baseline and/or one or more follow-up neuropsychological evaluations in sufficient data to calculate both FSIQ and EIQ (from subtests). The Wechsler Intelligence scales (WISC, age 6 – 15 years and 11 months and WAIS, age > = 16) were used. FSIQ and EIQ were calculated for each patient at baseline and at all follow-up evaluations. Mixed linear models analysis was performed to assess differences in EIQ and FSIQ, both at baseline and over time. Median age was 11.1 years. Median follow-up was 26 months. Ninety-five patients received chemotherapy. One hundred six patients received craniospinal irradiation (CSI). Seventeen patients (9%) developed posterior fossa syndrome. Twenty-nine patients (16%) required a ventriculoperitoneal shunt. At baseline, EIQ was 2.2 points (95% CI = 1.2–3.2) higher on average than FSIQ (P < 0.001). The disparity between EIQ and FSIQ persists over time (P = 0.012), with FSIQ losing 0.4 points/year (95% CI = 0.01–0.8) relative to EIQ. Neither gender nor age had an effect on the EIQ/FSIQ differences. RT Field, specifically CSI vs. no CSI and CSI dose, did not have an effect on the EIQ/FSIQ differences. EIQ systematically overestimates the FSIQ of children treated with cranial RT. Although more time consuming, FSIQ is more likely to identify neurocognitive deficits and allow for appropriate recommendations for academic services and accommodations in school. Because EIQ tends to underestimate adverse neurocognitive effects compared to FSIQ, it should have a very limited role as a tool in both clinical and research settings.Abstract 1161; Table 1Patients (%)Tests per patient196 (52%)260 (32%)322 (12%)4+8 (4%)Testing scheduleBaseline only72 (39%)Baseline + follow-up78 (42%)Follow-up only36 (19%) Open table in a new tab