Veterans Especially Vulnerable
Dr. Peskind, co-director of the VA Northwest Mental Illness Research, Education and Clinical Center, VA Puget Sound Health Care System, noted that while the veterans in the earlier study had at least one TBI, the average number was 20, and it was more common to have more than 50 mTBIs than to have a single one.
“These were highly exposed combat vets,” she said. “And that number doesn’t even account for subconcussive exposure to blasts, which now appear to cause detectable brain damage, even in the absence of a diagnosable TBI.”
The Maine shooter, Mr. Card, had not seen combat and was not assessed for TBI during a psychiatric hospitalization, according to The New York Times.
Dr. Peskind added that this type of blast damage is likely specific to individuals in the military. “It isn’t the sound that causes the damage,” she explained. “It’s the blast wave, the pressure wave, and there aren’t a lot of other occupations that have those types of occupational exposures.”
Dr. Snyder added that the majority of blast TBIs have been studied in military personnel, and she is not aware of studies that have looked at blast injuries in other industries, such as demolition or mining, to see if they have the same type of biologic consequences.
Dr. Snyder hopes that the researchers will follow the participants in the Neurology study and continue looking at specific markers related to Alzheimer’s disease brain changes. What the research so far shows “is that, at an earlier age, we’re starting to see those markers changing, suggesting that the underlying biology in people with mild blast TBI is similar to the underlying biology in Alzheimer’s disease as well.”
Michael Alosco, PhD, associate professor and vice chair of research, department of neurology, Boston University Chobanian & Avedisian School of Medicine, called the issue of blast exposure and TBI “a very complex and nuanced topic,” especially because TBI is “considered a risk factor of Alzheimer’s disease” and “different types of TBIs could trigger distinct pathophysiologic processes; however, the long-term impact of repetitive blast TBIs on neurodegenerative disease changes remains unknown.”
He coauthored an editorial on the earlier Neurology study that noted its limitations, such as a small sample size and lack of consideration of lifestyle and health factors but acknowledged that the “findings provide preliminary evidence that repetitive blast exposures might influence beta-amyloid accumulation.”
Clinical Implications
For Dr. Peskind, the “inflection point” was seeing lower CSF Abeta42, about 20 years earlier than ages 60 and 70, which is more typical in cognitively normal community volunteers.
But she described herself as “loath to say that veterans or service members have a 20-year acceleration of risk of Alzheimer’s disease,” adding, “I don’t want to scare the heck out of our service members of veterans.” Although “this is what we fear, we’re not ready to say it for sure yet because we need to do more work. Nevertheless, it does increase the index of suspicion.”
The clinical take-home messages are not unique to service members or veterans or people with a history of head injuries or a genetic predisposition to Alzheimer’s disease, she emphasized. “If anyone of any age or occupation comes in with cognitive issues, such as [impaired] memory or executive function, they deserve a workup for dementing disorders.” Frontotemporal dementia, for example, can present earlier than Alzheimer’s disease typically does.
Common comorbidities with TBI are PTSD and obstructive sleep apnea (OSA), which can also cause cognitive issues and are also risk factors for dementia.
Dr. Iliff agreed. “If you see a veteran with a history of PTSD, a history of blast TBI, and a history of OSA or some combination of those three, I recommend having a higher index of suspicion [for potential dementia] than for an average person without any of these, even at a younger age than one would ordinarily expect.”
Of all of these factors, the only truly directly modifiable one is sleep disruption, including that caused by OSA or sleep disorders related to PTSD, he added. “Epidemiologic data suggest a connection particularly between midlife sleep disruption and the risk of dementia and Alzheimer’s disease, and so it’s worth thinking about sleep as a modifiable risk factor even as early as the 40s and 50s, whether the patient is or isn’t a veteran.”
Dr. Peskind recommended asking patients, “Do they snore? Do they thrash about during sleep? Do they have trauma nightmares? This will inform the type of intervention required.”
Dr. Alosco added that there is no known “safe” threshold of exposure to blasts, and that thresholds are “unclear, particularly at the individual level.” In American football, there is a dose-response relationship between years of play and risk for later-life neurological disorder. “The best way to mitigate risk is to limit cumulative exposure,” he said.
The study by Li and colleagues was funded by grant funding from the Department of Veterans Affairs Rehabilitation Research and Development Service and the University of Washington Friends of Alzheimer’s Research. Other sources of funding to individual researchers are listed in the original paper. The study by Braun and colleagues was supported by the National Heart, Lung and Blood Institute; the Department of Veterans Affairs Rehabilitation Research and Development Service; and the National Institute on Aging. The white paper included studies that received funding from numerous sources, including the National Institutes of Health and the DOD. Dr. Iliff serves as the chair of the Scientific Advisory Board for Applied Cognition Inc., from which he receives compensation and in which he holds an equity stake. In the last year, he served as a paid consultant to Gryphon Biosciences. Dr. Peskind has served as a paid consultant to the companies Genentech, Roche, and Alpha Cognition. Dr. Alosco was supported by grant funding from the NIH; he received research support from Rainwater Charitable Foundation Inc., and Life Molecular Imaging Inc.; he has received a single honorarium from the Michael J. Fox Foundation for services unrelated to this editorial; and he received royalties from Oxford University Press Inc. The other authors’ disclosures are listed in the original papers.
A version of this article appeared on Medscape.com.