The link between a single traumatic brain injury (TBI) and the risk of developing dementia has been controversial for some time because of conflicting study results. Now, a new study finds that TBI is associated with an increased risk of dementia in adults 55 and older.
The study, published in JAMA Neurology and conducted by researchers at the University of California, San Francisco (UCSF), found that those with moderate to severe TBI at 55 or older, or mild TBI — also called a concussion — at 65 or older, had an increased risk of dementia.
The study included 164,661 patients who were identified in a California health database of emergency room and inpatient visits.
Lead study author Dr. Raquel C. Gardner, a behavioral neurologist and research fellow at the San Francisco Veteran’s Administration Medical Center and UCSF, examined the risk of dementia among seniors with recent TBI, compared to adults with non-TBI body trauma (NTT), which was defined as fractures, but not of the head or neck.
In the study, 51,799 patients with trauma, or 31.5 percent, had TBI. Of those, 8.4 percent developed dementia, compared with 5.9 percent of patients with NTT. The average time from trauma to dementia diagnosis was 3.2 years; and it was shorter in the TBI group compared to the NTT group.
Gardner told Healthline that previous studies have shown there is a small but increased chance of getting dementia later in life if you’ve had any kind of brain injury.
Gardner’s team wanted to look specifically at what happens when you get a brain injury when you are older. According to the Centers for Disease Control (CDC), the highest rates of TBIs occur in people who are older, and they are usually caused by falls, Gardner said.
“We wanted to really hone down and say, what is the chance you’ll get dementia just from the brain injury, above and beyond any of the other extraneous factors that might lead a person to fall and get a trauma in the first place?” Gardner said. “Is it possible the very same things that are leading someone to get dementia are also leading them to fall and get the brain injury? In that case, the dementia is not because of the brain injury; it’s because of all the other factors that lead them to get the fall in the first place.”
By comparing older adults with brain trauma to seniors with body trauma, the researchers eliminated the concern that they were comparing people with brain trauma to people who were otherwise very healthy.
Sixty-six percent of both the older adults who had brain trauma and those who had body trauma were injured due to falls. “The people in both groups were pretty similar, so we didn’t have to worry as much that the result we found was due to other extraneous factors. We were comparing people who really only differed on the fact that they injured their brain as opposed to their leg,” said Gardner.
The team found that there is about a 26 percent increased chance that an older adult will get dementia if they’ve had a TBI, as opposed to an injury elsewhere on their body.
When the researchers looked specifically at whether someone had a mild traumatic injury, sometimes called a concussion, or a more severe traumatic brain injury, they found that severe TBI was risky for everyone 55 and older.
“But when we looked at just the mild TBI, this was only significantly risky for people who were 65 and older. By the time folks were in their 70s or 80s, concussion, or mild TBI, seemed essentially as risky as a more severe TBI. That was the most surprising thing to learn, because these concussions appear to be more and more risky as we get older,” Gardner said.
Gardner acknowledged that the study was limited in that researchers used hospital billing codes to learn who had been diagnosed with TBI, broken legs, and dementia, and did not follow individual people over time in a regulated way. “So, certainly more research needs to be done,” said Gardner.
The key to developing treatments, cures, and prevention for dementia will be to figure out what is really going on in someone’s brain after they get a brain injury. “What are the mechanisms and biology behind these cases of dementia we are seeing after TBI?” Gardner asked.In a related editorial, Dr. Steven T. DeKosky of the University of Pittsburgh School of Medicine said the study lacked a nontrauma control group that “may have answered the question of whether NTT (i.e. body trauma itself) raised the risk of dementia significantly above age-equivalent controls without nonbrain trauma (perhaps from inflammation or other complications).”
Dr. Wayne Gordon, vice chair of the Department of Rehabilitation Medicine at the Icahn School of Medicine at Mount Sinai in New York, praised the new study’s use of a large set of patient data.
He added that current research shows about 20 percent of people with a moderate to severe injury who come to rehab die between two and five years after the injury.
“They are not necessarily dying of dementia or Alzheimer’s, but clearly TBI in some people results in some form of neurodegeneration. In some people it may be Alzheimer’s; in some folks with multiple brain injuries, whether they are athletes or not, it may be CTI (which is what football players have). We don’t know,” said Gordon. CTI stands for chronic traumatic encephalopathy and it is sometimes seen in the brains of retired professional football stars.
Gordon agreed with Gardner that more research is needed. “The more evidence we have about the long-term effects of TBI, the more we can understand what interventions are possible to inform and educate our patients appropriately. In elderly patients above the age of 45, it is clear that TBI accelerates the aging process and basically hastens death. In this particular study, there’s an increased prevalence of dementia, and that is not at all surprising to me,” Gordon said.