Barnes DE, Byers AL, Gardner RC, Seal KH, Boscardin J, Yaffe K. Association of mild traumatic brain injury with and without loss of consciousness with dementia in U.S. military veterans. JAMA Neurol. 2018 May 7.

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  1. The manuscript by Barnes and colleagues illustrates the power of epidemiologic data to demonstrate important findings and point the way forward for prospective studies.  That moderate to severe TBI leads to losses of function, decreased cognitive reserve and greater risk of subsequent dementia, has been postulated for years, and here are data that demonstrate it. The findings that various categories of milder TBI, without or with reported loss of consciousness (LOC), also lead to elevated risks with increasing severity of the TBI are perhaps more surprising, especially in TBI with no loss of consciousness. However, veterans in all likelihood are subject to multiple sub-concussive TBIs in training and in deployments in a combat zone, as well as blast waves both in training and in combat. Thus, this population in all likelihood has had a number of head traumas, and we know such exposures are likely to have adverse outcomes. The authors note that exact diagnostic criteria cannot be obtained, but the power of this Big Data set indicates a heightened need for monitoring of servicemen in both training and deployment, for setting thresholds for exposure, and for developing new methods of deflecting brain injury (different helmets, blast wave ameliorating shields, etc.) as recommended in a recent report from the Center for New American Security. Thus the manuscript provides a strong rationale to take the next step—a prospective study.

    View all comments by Steven DeKosky

  2. This study, in veterans, adds to the growing literature showing an association between TBI and dementia.  There is still a critical need to extrapolate this work to individuals in the general population because there are a lot of people who experience a TBI yet do not develop dementia. We need to identify which characteristics (e.g., severity of head trauma, genetics, demographics, comorbidities) interact with the TBI to place a person at greater risk of dementia and to develop risk models that could be used clinically.

    View all comments by Michelle Mielke

  3. These results are similar to those from the recent Danish study showing a dose dependent increase in hazard ratio with increasing severity of TBI (Fann et al., 2018), and about double the risk even in mild TBI without loss of consciousness (LOC) . As the authors note, there is only one paper prior to Fann et al. showing this increased risk in mild TBI (Lee et al., 2013) . The strengths and limitations are largely as described by the authors. With respect to risk for dementia in veterans with combat-related, largely blast-induced and repetitive mild TBI, it is probably too early to see much incident dementia because of the young age of this particular subset of veterans in the sample. Again, among the limitations are probable under diagnosis of both mild TBI in the CTBIE database and dementia overall within the VA. Given that despite these limitations, an increased hazard ratio was still found, even for mild TBI without LOC, raises concerns about long-term risk of dementia in veterans with TBI.

    References:

    Fann JR, Ribe AR, Pedersen HS, Fenger-Grøn M, Christensen J, Benros ME, Vestergaard M. Long-term risk of dementia among people with traumatic brain injury in Denmark: a population-based observational cohort study. Lancet Psychiatry. 2018 May;5(5):424-431. Epub 2018 Apr 10 PubMed.

    Lee YK, Hou SW, Lee CC, Hsu CY, Huang YS, Su YC. Increased risk of dementia in patients with mild traumatic brain injury: a nationwide cohort study. PLoS One. 2013;8(5):e62422. Print 2013 PubMed.

    View all comments by Elaine R Peskind

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