Traumatic Brain Injury
Part 1: Introduction and Brief Epidemiology
Mark Scheutzow, M.D., Ph.D., MHA, MPH
Traumatic brain injury (TBI) increases the chances of developing dementia with aging, including Alzheimer’s disease (AD). Theories that attempt to explain the development of dementia after TBI are primarily based on observations of AD-associated amyloid and tau pathologies in the brain after injury. However, it has been shown that pathology of this type is found only in a subset of patients after TBI.
There is only scant clinical evidence supporting a direct link between these types of pathological injuries and the development of dementia later in life. To explore this topic we’ll summarize epidemiological studies that find TBI is associated with increased risk of developing not just AD, but different types of dementia.
The second installment will investigate why amyloid and tau pathology is seen in only a subset of patients after TBI. The emerging hypothesis is that a single moderate to severe TBI increases the risk of developing late onset AD while repeat TBIs increase the risk of developing chronic traumatic encephalopathy.
We’ll then explore the suggestion that multiple manifestations of TBI induced neurodegenerative disorders be classified as trauma induced neurodegeneration, or traumatic encephalopathy
Up to 4 million TBIs occur annually in the US. The detrimental effects of repeat mild TBI (mTBI) in sports has been known for almost 100 years. At that time it was known as traumatic encephalitis. In 1928 the punch-drunk disorder in professional boxers cited clumsiness, ataxia, and disorientation as predominant symptoms. Chronic traumatic encephalopathy (CTE) is the term now used to describe the neuropathological changes occurring as a result of repeat concussive blows to the head. CTE can manifest with aspects of AD, frontotemporal dementia (FTD), Parkinson’s disease (PD), and amylotrophic lateral sclerosis (ALS).
There is still quite a bit of controversy as to whether a single moderate to severe TBI triggers the development of late onset dementia. AD makes up around 75% of all dementias and investigations have primarily focused specifically on the development of AD after TBI. Given the studies so far conducted, including meta-analyses, it seems that TBI increases the risk of developing AD by about 80%.
Interestingly, females have a reduced risk of developing AD after TBI. A group of WWII Marines and Navy soldiers who experienced a TBI were investigated and showed increased risk for multiple types of dementias, not just AD. Two retrospective case-control studies of veterans found that TBI increases the risk of developing frontotemporal dementia, (O.R. = 3.3 and 4.4). There is also an age discrimination effect: when TBI occurs more than 10 years prior to disease onset, the risk of AD is 1.63 however when it occurs within 10 years the risk increases to 5.33.
There is no doubt that TBI is a risk factor for different types of dementia.
What we’ll consider next month is whether TBI should be viewed as a trigger for individual neurodegenerative diseases or whether TBI creates an umbrella disease that has different outcomes.
Mark H. Scheutzow, M.D., Ph.D., MHA, MPH, of Asheboro, NC, received his Doctorate of Medicine and of Philosophy from Ohio State University College of Medicine, Columbus, OH, and his Master of Health Administration/Master in Public Health from UNC Gillings School of Global Public Health, Chapel Hill, NC. Over the last five years he has completed over 1700 continuing medical education hours in pain, addiction, and psychiatric medicine, as well as training in Age Management Medicine. He is certified by, and a Diplomat of the American Board of Addiction Medicine, certified by, and a Diplomat of the American Academy of Pain Management, was a Founding Diplomat of the American Board of Holistic Medicine, and is a Fellow and Board Member of the American Association of Integrative Medicine. He practices Interventional and Chronic Pain Medicine, Addiction Medicine, Addiction Psychiatry and Regenerative Pain Medicine, in Winston-Salem and Greensboro, NC. Dr. Scheutzow can be reached at firstname.lastname@example.org.
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