A mild traumatic brain injury (TBI) that does not result in a loss of consciousness is still associated with a long-term risk for dementia in veterans, according to a study published in JAMA Neurology.
Patients from the Veterans Health Administration healthcare system who had a TBI diagnosis (n=178,779) were compared with a propensity-matched comparison group without TBI (n=178,779). All patients were free from dementia at baseline. Investigators classified TBI severities as “mild without loss of consciousness,” “mild with loss of consciousness,” “mild with loss of consciousness unknown,” and “moderate or severe,” as defined by the US Department of Defense or Defense and Veterans Brain Injury Center criteria. The primary outcome was a dementia diagnosis.
A greater proportion of patients with a TBI developed dementia during the study period compared with those without TBI (6.1% vs 2.6%, respectively). Adjustment for medical and psychiatric comorbidities as well as demographics yielded dementia hazard ratios for mild TBI without loss of consciousness, mild TBI with loss of consciousness, mild TBI with loss of consciousness status unknown, and moderate to severe TBI of 2.36 (95% CI, 2.10-2.66), 2.51 (95% CI, 2.29-2.76), 3.19 (95% CI, 3.05-3.33), and 3.77 (95% CI, 3.63-3.91), respectively.
There was a shorter mean time from the index date to the dementia diagnosis among those with TBI vs those without TBI (3.6 vs 4.8 years, respectively). Overall, a diagnosis of dementia occurred approximately 1.5 years earlier among patients with TBI compared with those without TBI.
The retrospective analysis precluded the investigators’ ability to determine whether the diagnoses of TBI and dementia followed standardized consensus definitions.
Investigators theorize that “mild TBI without [loss of consciousness] may increase dementia risk primarily by accelerating atrophy, while moderate to severe TBI may have a more direct effect on amyloid β and tau concentrations.”
Barnes DE, Byers AL, Gardner RC, et al. Association of mild traumatic brain injury with and without loss of consciousness with dementia in US military veterans [published online May 7, 2018]. JAMA Neurol. doi: 10.1001/jamaneurol.2018.0815