Multiple Head Injuries and Chronic Traumatic Encephalopathy (CTE)

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Multiple Head Injuries and Chronic Traumatic Encephalopathy (CTE): When do I need to worry about long-term complications of recurrent concussions?

There is currently no evidence to suggest that a single simple concussion event, treated appropriately, should cause any long-term complications. However, complex concussions or multiple head injuries can be a different story.

A concussion, also known as Traumatic Brain Injury (TBI), typically occurs from a head injury and results in damage to brain cells. This damage may be temporary, as seen in mild TBI (mTBI), or long-term, as with complex injuries or multiple head injuries. Though it is important to note that not all head injuries result in TBI. Chronic traumatic encephalopathy (CTE) is a degenerative disease found in those with a history of multiple head injuries. TBI and CTE can occur as a result of sports injuries, falls, and car accidents, among many others.

Ongoing studies look at the possible long-term complications of mTBI, including the largest known brain looking at brain autopsies for pathologic signs of CTE. Much of this research is in process, but conclusive evidence that mTBI causes CTE has not yet been found. However, one study has shown ample correlative data among 98% of former NFL player brain autopsies to insight some very scary concerns with the repercussions of recurrent head injuries over time. Below is a brief review of some of the important research and factors regarding this very complex conversation about the risk of multiple head injuries.

What is CTE?

Simply put this is a pathologic diagnosis based on brain tissue changes that occur over time in those exposed to recurrent brain trauma over many years and is similar to Alzheimer’s. The link to clinical symptoms has yet to be well established, but many of these patients suffered from severe cognitive decline, mood/personality changes, and physical symptoms.

What DO we know about CTE?

We know that professional athletes with recurrent head trauma over time seem to have a very high likelihood of developing these changes in the brain. We know that they may be linked to clinical manifestations of brain degeneration such as memory loss and depression. We know recurrent trauma to the brain (diagnosed as concussion or not) seems to be the driving factor for developing CTE. We also know that CTE is found at a much higher rate in athletes involved in collision sports (such as football) than in the general population. We know that case studies looking at brain autopsies of former football players show alarming rates of this disease. Dr. Ann McKee of Boston University is currently leading the largest ongoing CTE study. Dr. McKee and her team have examined the brains of 112 former NFL players who donated their brains to research after death and found that 110 of them had CTE. This same study also found evidence of CTE in 48 out of 53 college football players.

We know this is scary and we need to do more research and utilize our resources to learn more to best prevent CTE.

What do we NOT know?

Despite the concerning link of CTE to sports like football, we do not yet have evidence of its causality. This is sort of a “chicken or the egg” question. Did CTE come before the clinical symptoms or did the clinical symptoms help drive CTE? Could other factors like depression and substance abuse lead to brain changes similar to CTE? Given the nature of brain injury research, it is very difficult to run controlled randomized trials to prove causality. With that said, the correlative data coming from brain banks such as Boston University is still very alarming.

We don’t know to what degree the manifestations of CTE lead to clinical problems and what other variables are playing a role (e.g., substance use, stress, education, etc.).

We don’t have great data on CTE findings in the general population (small studies) or even across the entire NFL or NCAA population. This is because donated brains are typically in symptomatic patients, which can inflate percentages when looking at case studies.

Most importantly, we don’t know HOW much head trauma is too much. There is currently no magic number or well-established measure to determine the threshold at which multiple head injuries become a serious risk for long-term complications or CTE. This makes it difficult to answer return to play decisions in young contact athletes with multiple head injuries. These cases need to be considered individually, understanding all the details of each head injury, testing for any residual deficits, and depend on the level of risk associated with the athlete’s sport. We need to understand not only the athlete’s concussion history, but also their world with respect to the sports they play and love the most. Ultimately, when all the specifics of each unique case have been dissected, an informed decision can be made after assessing all risks and benefits of continuing with a contact sport.


This is a very complicated topic with multiple layers of consideration and thus there is no single answer for all head injury cases. We now have some alarming information on recurrent brain injuries that we previously did not understand,  but much of the details remain inconclusive until the research evolves further.

  • Recurrent head traumas are not good for the brain and there should be limits at which we thoughtfully consider early retirement or transition for a high-risk sport.  Those limits are determined case-by-case and expert opinion from a head injury specialist will be critical.
  • Taking extreme actions such as banning sports or dropping programs at this time are not supported by the evidence. The goal should be to make our contact sports safer utilizing rule changes, legislative changes, and mandating up to date expert standard of care for evaluation of head injuries and return to play decisions.



By Mo Mortazavi, MD


Read more:
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Concussion and Benign Paroxysmal Positional Vertigo
Dysautonomia and Concussion
VOMS Assessment: A Healthy Balance
Active Rehabilitation Protocol (ARP)
Neurocognitive Assessment and ICAP for Concussions

Keywords: Multiple Head Injuries, Chronic Traumatic Encephalopathy (CTE), long-term complications of recurrent concussions, recurrent concussions, recurrent head injuries, brain tissue changes, recurrent brain trauma, Alzheimer’s, severe cognitive decline, mood/personality changes, NFL brain autopsies, Brain bank, Boston University, Ann McKee