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Incidence and risk of attention-deficit/hyperactivity disorder and learning disability by adulthood after traumatic brain injury in childhood: a population-based birth cohort study.

The aim of this study was to understand the risk of developing attention-deficit/hyperactivity disorder (ADHD) or learning disability (LD) after childhood traumatic brain injury (TBI) in a population-based birth cohort. Cases of TBI for children from birth to 10 years were confirmed and stratified by severity of injury. For each TBI case, two age-matched and sex-matched referents without TBI were identified from the same birth cohort. Presence of ADHD and LD before age 19 were confirmed using medical and/or school records. Associations between TBI exposure and subsequent ADHD or LD were assessed in multivariable Cox regression models, adjusting for maternal age, education, and race. The incidence rate of TBI before age 10 was 1,156 per 100,000 person-years. Children who had a TBI before age 10 were more likely to have met the research criteria for ADHD (hazard ratio [HR], 1.68; 95% CI, 1.15-2.45) or LD (HR, 1.29; 95% CI, 1.00-1.68) by age 19. No statistically significant associations were shown between TBI and ADHD or LD when restricted to definite and probable TBI cases (consistent with moderate to severe and mild TBI, respectively) and their referents. Significant associations were shown when the analysis was confined to possible TBI cases (consistent with concussive TBI) and their referents (ADHD: HR, 2.05; 95% CI, 1.31-3.20; and LD: HR, 1.42; 95% CI, 1.05-1.91). Increased risk for developing ADHD and LD by adulthood was shown particularly for children with the least-severe injuries, indicating that factors other than trauma-related altered brain function likely contribute to this risk.