Association between Paediatric Mild Traumatic Brain Injury and Two-Year Psychiatric Outcomes Largely Explained by Pre-Existing Mental Health Problems

Background Evidence that mild traumatic brain injury (mTBI) causes psychiatric problems in children has been mixed. Investigating this issue has been difficult due to the lack of representative longitudinal data on child mTBI that includes adequate measures of subsequent mental health symptoms and service use in young people. Methods We used data from the ABCD longitudinal cohort study to examine the association between mTBI and psychiatric diagnoses, symptoms, and psychiatric service use in over 11,000 children. In both children reporting i) previous mTBI at baseline; and ii) previously uninjured children reporting new cases of mTBI since baseline, we examined psychiatric outcomes and service use at two-year follow-up. We also compared mTBI cases to a comparison group of participants with orthopaedic injury but without mTBI. Mixed-effects models were used and adjusted for demographic and social covariates, with missing data imputed using random forest multiple imputation. To account for baseline mental health, we used propensity-score matching to identify a comparison sample matched on confounding variables and baseline outcome measures. Results When examined without adjustment for baseline mental health, both lifetime mTBI at baseline, and new occurrence of mTBI at two-year follow-up, were reliably associated with an increased risk of DSM-5 anxiety and behavioural disorders, a range of psychiatric symptom scores, and increased service use. Controlling for baseline mental health in the mTBI group using propensity-score matching eliminated all statistically reliable associations apart from anxiety disorder diagnosis and symptoms which remain associated at two-year follow-up. Evidence for association with subsequent mental health service use was inconsistent. Conclusion Anxiety was the only mental health outcome reliably associated with mTBI when baseline mental health was accounted for. Regardless of potential causality, children with mTBI are likely to present with high levels of mental health difficulties, and this remains an important comorbidity that clinicians should be aware of. Key points Evidence that mild TBI (mTBI) causes psychiatric problems in children has been mixed Longitudinal studies including measures of paediatric mTBI and pre- and post-injury psychiatric problems are required This longitudinal study examined the association between mTBI and psychiatric diagnoses, symptoms, and psychiatric service use in over 11,000 children aged 9-10 at baseline, and new cases of mTBI in the two years following baseline Higher levels of psychiatric problems and service use were associated with lifetime and new occurrence of mTBI, suggesting that paediatric mTBI should be considered a clinical marker for greater mental health attention and monitoring These associations were largely eliminated, or appeared equally in the orthopaedic injury comparison group, once pre-existing mental health problems were accounted for, apart from associations with anxiety and psychiatric medication use, which remained reliable. This suggests that, overall, there is limited evidence for a causal relationship between mTBI and new psychiatric problems, but that there may be evidence for a causal relationship between mTBI, anxiety problems and psychiatric medication use.