Relative Risk of Mortality after Traumatic Brain Injury: A Population-Based Study of The Role of Age And Injury Severity

To test if observed vs. expected mortality differs by age among traumatic brain injury (TBI) cases, a population-based, historical cohort study was conducted in Olmsted County, Minnesota. From all residents with any diagnosis suggestive of TBI 1985–1999, we randomly sampled 7,800 and reviewed their medical records to confirm the event. Confirmed incident cases were categorized by age in years (<16 = pediatric, 16–65 = adult, > 65 elderly) and severity (moderate/severe vs. mild) and followed for vital status through 6/30/2004. We compared observed 6-month and 10-year mortality with expected and tested if the differences varied by age. Of 1,433 confirmed incident cases, 35% were pediatric; 55% were adult; only 9% were elderly; 11.2% of all cases were moderate/severe; the proportions by increasing age group were 11.4%, 8.5%, 26.7%. The proportions who died within 6 months increased with increasing age group, both for moderate/severe (10.3%, 40.3%, 50.0%) and mild cases (0%, 0%, 9.1%); mortality for moderate/severe cases was nearly 40 times that for mild cases, independent of age. Among 6-month survivors, 10-year mortality differed from expected only for adult cases. For all cases, after adjusting for sex, year of TBI, and severity, the difference between observed and expected 10-year mortality was greater for adult cases than for pediatric cases and similar for adult and elderly cases. Elderly individuals account for <10% of TBI cases and >50% of 10-year mortality, yet much of this discrepancy reflects age-associated mortality in general. Findings have implications for (1) reducing the number of excess deaths following TBI and (2) caring for survivors.