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Original Investigation
September 2018

Association of Mild Traumatic Brain Injury With and Without Loss of Consciousness With Dementia in US Military Veterans

Author Affiliations
  • 1San Francisco Veterans Affairs Health Care System, San Francisco, California
  • 2Department of Psychiatry, University of California, San Francisco
  • 3Department of Epidemiology and Biostatistics, University of California, San Francisco
  • 4Department of Neurology, University of California, San Francisco
  • 5Department of Medicine, University of California, San Francisco
JAMA Neurol. 2018;75(9):1055-1061. doi:10.1001/jamaneurol.2018.0815
Key Points

Question  Is mild traumatic brain injury without loss of consciousness associated with an increased risk of dementia diagnosis in veterans?

Findings  In this propensity-matched cohort study of more than 350 000 veterans with and without traumatic brain injuries, mild traumatic brain injury without loss of consciousness was associated with more than a 2-fold increase in the risk of dementia diagnosis, even after adjusting for medical and psychiatric comorbidities.

Meaning  Even mild traumatic brain injuries that do not result in loss of consciousness might have long-term neurodegenerative consequences.

Abstract

Importance  Traumatic brain injury (TBI) is common in both veteran and civilian populations. Prior studies have linked moderate and severe TBI with increased dementia risk, but the association between dementia and mild TBI, particularly mild TBI without loss of consciousness (LOC), remains unclear.

Objective  To examine the association between TBI severity, LOC, and dementia diagnosis in veterans.

Design, Setting, and Participants  This cohort study of all patients diagnosed with a TBI in the Veterans Health Administration health care system from October 1, 2001, to September 30, 2014, and a propensity-matched comparison group. Patients with dementia at baseline were excluded. Researchers identified TBIs through the Comprehensive TBI Evaluation database, which is restricted to Iraq and Afghanistan veterans, and the National Patient Care Database, which includes veterans of all eras. The severity of each TBI was based on the most severe injury recorded and classified as mild without LOC, mild with LOC, mild with LOC status unknown, or moderate or severe using Department of Defense or Defense and Veterans Brain Injury Center criteria. International Classification of Diseases, Ninth Revision codes were used to identify dementia diagnoses during follow-up and medical and psychiatric comorbidities in the 2 years prior to the index date.

Main Outcomes and Measures  Dementia diagnosis in veterans who had experienced TBI with or without LOC and control participants without TBI exposure.

Results  The study included 178 779 patients diagnosed with a TBI in the Veterans Health Administration health care system and 178 779 patients in a propensity-matched comparison group. Veterans had a mean (SD) age of nearly 49.5 (18.2) years at baseline; 33 250 (9.3%) were women, and 259 136 (72.5%) were non-Hispanic white individuals. Differences between veterans with and without TBI were small. A total of 4698 veterans (2.6%) without TBI developed dementia compared with 10 835 (6.1%) of those with TBI. After adjustment for demographics and medical and psychiatric comobidities, adjusted hazard ratios for dementia were 2.36 (95% CI, 2.10-2.66) for mild TBI without LOC, 2.51 (95% CI, 2.29-2.76) for mild TBI with LOC, 3.19 (95% CI, 3.05-3.33) for mild TBI with LOC status unknown, and 3.77 (95% CI, 3.63-3.91) for moderate to severe TBI.

Conclusions and Relevance  In this cohort study of more than 350 000 veterans, even mild TBI without LOC was associated with more than a 2-fold increase in the risk of dementia diagnosis. Studies of strategies to determine mechanisms, prevention, and treatment of TBI-related dementia in veterans are urgently needed.

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