For the analysis, researchers compared cognitive test results for veterans with mild traumatic brain injury (mTBI), an IQ and age-matched group of veterans without mTBI, healthy controls without military experience, and an IQ-matched group of early-stage Parkinson disease patients without dementia. Parkinson disease patients had a neurologist-confirmed diagnosis with advanced cases screened out; mTBI cases were based on injuries with loss of consciousness for 30 minutes or less, without substantial memory loss or confusion for the period within 24 hours of injury.
The main outcomes assessed in the analysis were time to completion for the Trail Making Test -A and -B (TMT-A, TMT-B), which researchers used to examine how participants performed in domains such as cognitive flexibility, attention, processing speed, memory, and inhibitory control.
Mean number of seconds to complete TMT-A was significantly lower for healthy controls (25.4) and veterans without mTBI (24.8) than for veterans with mTBI (33.5) and older individuals with early-stage Parkinson disease (36.8)
Similarly, mean seconds to complete TMT-B were significantly lower for healthy controls (49.5) and veterans without mTBI (51.8) than for veterans with mTBI (78.3) and those with Parkinson disease (98.1).
With both TMT-A and TMT-B, there was no significant difference between scores for veterans with mTBI and older individuals with Parkinson disease, the study team reports in PLoS ONE.
In one primary outcome of interest, decision-making on the TMT-B test, veterans with mTBI took 26.5 to 28.8 seconds longer to completion than age- and IQ-matched veterans and healthy controls, respectively.
"That does not seem like a big difference, but what was totally unexpected was the extent of decline in cognitive flexibility, attention, inhibitory control, processing speed, and working memory that was similar to individuals with and without Parkinson's disease who were three to four decades older," said lead study author Vicki Nejtek, an associate professor in pharmacology and neuroscience at the University of North Texas Health Science Center in Fort Worth.
One challenge for treating veterans with mTBI is that they may not disclose these injuries or speak up when they experience changes in their cognitive function, Nejtek said by email.
"First and foremost, veterans, in particular are thought of as stoic individuals and they may not want to be perceived as being weak or impaired in any way, and they would most likely not want to be sidelined from their duties," Nejtek said. "Thus, they may not complain about their symptoms while this sets the stage for 'silent' neurodegeneration."
Some veterans may also write off any cognitive symptoms as a byproduct of chronic stress, Nejtek added. Because they don't necessarily seek medical care for mild cognitive issues, veterans with mTBI may not fully realize the extent of their cognitive problems until it worsens to the point that it becomes noticeable to others or it impinges on their ability to function with precision in the way they did before their injuries.
Beyond its small size, another limitation of the study is that results from veterans may not be generalizable to other populations.
The study excluded a wide range of individuals including pregnant people, those who didn't speak English, and people with endocrine, autoimmune, rheumatological, cardiovascular, psychiatric, or neurological conditions other than Parkinson disease. The study also excluded people with physical or sensory limitations as well as individuals who had alcohol or legal or illegal substance use that might interfere with their performance on cognitive tests.
However, the results do underscore the importance of clinicians routinely screening for cognitive problems even in younger patients with a history of mTBI, Nejtek said.
"Current clinical practice would not necessarily ask young patients about cognitive difficulties unless a patient or their loved ones complain about bothersome symptoms or problems," Nejtek said. "Ideally, patients at any age would benefit from a change in clinical practice where the clinician asks a few screening questions about their exposures to possible mTBI-related events."
SOURCE: https://bit.ly/3JeIUJr PLoS ONE, online November 17, 2021.
By Lisa Rapaport
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