The question of whether traumatic brain injury causes dementia has long been debated, and the results of various research are sometimes contradictory. However, there is increasing evidence that severe brain injury can result in long-term brain damage.
Traumatic brain injuries (TBIs) cause the brain’s normal function to be disrupted. According to the Centers for Disease Control and Prevention, they are caused by a blow or jolt to the skull, or an injury that penetrates it (CDC).
In the United States in 2013, 2.8 million people had a TBI, with around 56,000 of them dying. Small children under the age of four, teens and young adults between the ages of 14 and 25, and people over the age of 75 were the age groups most impacted by TBI. Falls, being struck by an item, and automobile accidents were the most prevalent causes of TBI.
Headaches, blurred vision, slurred speech, and short-term memory impairments are just a few of the early symptoms. TBIs can potentially have long-term health consequences, including an increased risk of seizures and infections.
TBI has been linked to numerous kinds of progressive neurodegeneration, including dementia, Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), and Parkinson’s disease, according to research, however the evidence is mixed.
Why is it so difficult to come up with irrefutable proof? What are the long-term prospects for TBI victims?
The latest findings
The researchers reviewed medical notes of working-age adults under the age of 65 who had mild or moderate to severe TBI and later got dementia, Parkinson’s disease, or ALS, using the Finnish Care Register for Health Care.
They detected a correlation between moderate to severe TBI and dementia, but no such association was found with Parkinson’s disease or ALS.
Importantly, they discovered that dementia rates in moderate to severe TBI patients were comparable to those in the general population. However, dementia primarily affects the elderly, indicating that TBI raises the risk from old age to working age.
Finland has a tax-funded healthcare system, hence the dataset utilized in this study was extensive. All acute TBI cases are treated in public hospitals, according to the authors, and hence would have been included in the research.
However, data was only accessible for TBI patients who had been hospitalized to the hospital with neurodegenerative symptoms afterward. Other individuals with a diagnosis of neurodegeneration may have been overlooked if they had not been hospitalized at the time, according to the authors.
The findings of the Finnish study matched data published in the Asian Pacific Journal of Public Health last year. Dementia rates were greater among Taiwanese TBI patients than among non-TBI patients in this study.
Another research, just published in the Journal of Alzheimer’s Disease, found no association between TBI and Alzheimer’s disease.
The scientists studied 706 seniors in the United States with and without TBI and discovered that TBI had no effect on cognitive deterioration. However, because TBI was self-reported rather than assessed in the research participants’ medical records, the results may not have been reliable.
The Annals of Physical and Rehabilitation Medicine released a systematic study earlier this year that struggled to identify a relevant link between TBI and Alzheimer’s disease.
Although the evaluation contained 18 trials, the authors were unable to categorize TBI according to severity. It may not have been able to establish a link between TBI and Alzheimer’s disease if mild and moderate to severe TBI were lumped together.
Other disease, on the other hand, has discovered clear correlations between TBI and Alzheimer’s and Parkinson’s disease.
TBI, neurodegeneration link supported
According to a recent study published in the journal The Clinical Neuropsychologist, people with histories of moderate to severe TBI began to experience symptoms and obtained their diagnosis 2.5 years earlier than non-TBI patients in an Alzheimer’s disease patient cohort. However, in this study, TBI was self-reported.
While there was no association between TBI and dementia or Alzheimer’s disease, there was a correlation with Parkinson’s disease, according to a study published in JAMA Neurology last year.
After their deaths, several of the research participants agreed to have their brains autopsied. Both mild and moderate to severe TBI patients displayed evidence of Lewy bodies, a hallmark of Parkinson’s disease, in their brains, as well as signs of cerebral microinfarcts in the moderate to severe TBI patients.
Importantly, while the majority of research participants were 65 and older, a third of mild TBI patients and almost half of moderate to severe TBI patients were 25 or younger at the time of their injury. This shows that TBI may have long-term neurodegenerative consequences.
The difficulty with this sort of study is that it relies heavily on association measurements. This implies that researchers use data to determine whether or if there is a relationship between TBI and neurodegeneration in a certain study group.
However, because cause and effect cannot be shown in these investigations, additional biological pathways may be implicated in producing neurodegeneration in these patients.
Animals are used by researchers to investigate what occurs in the brain after a TBI. The events that followed TBI are starting to be pieced together here.
How can TBI cause neurodegeneration?
A recent paper in Reviews in the Neurosciences detailed what is known about the neurological damage that occurs after a TBI to date.
Blood arteries, neurons, and other cell types are all damaged in the first insult. Neurons get overstimulated as a side consequence, resulting in oxidative stress and cell death. The brain’s water metabolism is also disrupted, resulting in edema.
The blood-brain barrier is compromised, enabling immune cells to invade the injured brain, which is ordinarily resistant to most drugs.
The brain can be permanently harmed by a combination of oxidative damage, neuroinflammation, edema, and poor blood flow.
A recent research published in The Journal of Neuroscience used a mouse model of brain damage to analyze the long-term repercussions of TBI in greater depth.
The areas surrounding the injury site suffered immediate damage. Importantly, persistent neuroinflammation was found to cause long-term damage in distant areas of the brain.
Long-term consequences following TBI were also detected in a mouse model of Alzheimer’s disease, according to a study published in Neuroscience Letters. There were no immediate alterations in the brains of older mice who had received TBI vs those who had not.
For the first week of the trial, both wounded and uninjured mice acquired senile plaques, a characteristic of Alzheimer’s disease. The mice, on the other hand, had much more plaques 28 days after the TBI. There was also a problem with spatial learning.
The researchers deduced that TBI hastens the onset of Alzheimer’s disease symptoms.
What do these findings imply for people who have had a TBI?
The need for long-term monitoring
While it is feasible to examine the cellular processes that occur after TBI in model systems, applying these findings to real patients is more problematic.
Many studies show that TBI has long-term repercussions on the brains of animals and people, but the amount of the damage and its consequences are unknown.
Regardless of their findings, most studies agree that TBI patients, particularly those who have suffered moderate to severe TBI, require long-term monitoring. There is also a request for more precise diagnostic criteria that would allow doctors to detect TBI-related neurodegeneration earlier.
This would allow doctors to keep a close eye on their patients and provide therapies or interventions as soon as possible, therefore delaying the process of cognitive deterioration.
More research is clearly needed, particularly studies that look into cause and effect and can relate the findings to large-scale, reliable demographic data.
It’s also important to keep in mind that not everyone who has had a TBI will develop progressive neurodegeneration.
A total of 1.6 percent of patients with a history of moderate TBI developed dementia in the Finnish research. Even while individuals with moderate to severe TBI were 90 percent more likely to be diagnosed with dementia, the rate was still just 3.5 percent.
While there is solid evidence that a TBI may cause long-term brain damage, concerns remain about why certain patients acquire progressive neurodegeneration and how many people are likely to be impacted.