Post-concussion symptoms and disability in adults with mild traumatic brain injury: a systematic review and meta-analysis.

Studies investigating long-term symptoms and disability after mild traumatic brain injury (mTBI) have yielded mixed results. This systematic review and meta-analysis aimed to determine the prevalence of self-reported post-concussion symptoms (PCS) and disability following mTBI. We systematically searched MEDLINE, Embase, CINAHL, CENTRAL, and PsycInfo to identify inception cohort studies of adults with mTBI. Paired reviewers independently extracted data and assessed risk of bias with the Scottish Intercollegiate Guidelines Network criteria. We identified 43 eligible studies for the systematic review; 41 were rated as high risk of bias, primarily due to high attrition (>20%). Twenty-one studies (49%) were included in the meta-analyses (5 studies were narratively synthesized; 17 studies were duplicate reports). At 3-6 months post-injury, the estimated prevalence of PCS from random-effects meta-analyses was 31.3% (95% CI=25.4-38.4) using a lenient definition of PCS (2-4 mild severity PCS) and 18.3% (95% CI=13.6-24.0) using a more stringent definition. The estimated prevalence of disability was 54.0% (95% CI=49.4-58.6) and 29.6% (95% CI=27.8-31.5) when defined as Glasgow Outcome Scale-Extended <8 and <7, respectively. The prevalence of symptoms similar to PCS was higher in adults with mTBI versus orthopedic injury (prevalence ratio=1.57, 95% CI=1.22-2.02). In a meta-regression, attrition rate was the only study-related factor significantly associated with higher estimated prevalence of PCS. Setting attrition to 0%, the estimated prevalence of PCS (lenient definition) was 16.1%. We conclude that nearly 1 in 3 adults who present to an emergency department or trauma centre with mTBI report at least mild severity PCS 3-6 months later, but controlling for attrition bias, the true prevalence may be 1 in 6. Studies with representative samples and high retention rates are needed. Keywords: traumatic brain injury; head trauma; adult brain injury.