Can Concussions Lead to Parkinson’s Disease?

While the risk for head injuries in collision sports — high-contact sports like football, hockey, or boxing that regularly involve hitting other people — is well known, only in recent years have athletes and fans alike become more aware of the long-term impact that these injuries, and concussions in particular, can have on the brain.

Repeated hits to the head have already been tied to chronic traumatic encephalopathy (CTE), a brain disease linked to higher rates of dementia, depression, and mood disorders that has been found posthumously in the brains of hundreds of retired professional football players; about 34% of living former football players also believe they have CTE, according to a new study published in the Journal of the American Medical Association. This spotlight on head trauma in collision sports is now raising questions about whether movement disorders like Parkinson’s disease can be tied to concussions as well.

Health Matters spoke with Dr. James Noble, a neurologist at NewYork-Presbyterian/Columbia University Irving Medical Center, and Dr. Thomas Bottiglieri, a sports medicine physician at NewYork-Presbyterian/Columbia University Irving Medical Center, to understand more about the risk that concussions and other head trauma pose for Parkinson’s disease.

Dr. Noble: Concussions in isolation are not known to cause Parkinson’s disease or parkinsonism, which is a general term for physical changes that indicate key neurological changes that we see in some older adults. However, activities associated with concussions, such as exposure to repetitive head impacts (RHIs) over many years, have been associated with developing parkinsonism later in life.

It’s important to define the terms parkinsonism and Parkinson’s disease because parkinsonism doesn’t just occur in people with Parkinson’s disease; it is seen in a range of conditions associated with aging, including dementia and Alzheimer’s disease. Signs of parkinsonism include tremors or rhythmic shaking; walking or moving more slowly; stiffness in the arms, legs, or neck muscles; and balance problems. If someone has these occurring together, particularly when they begin with a tremor on one side while the body is at rest, they may be diagnosed with Parkinson’s disease. With Parkinson’s disease, it’s also expected that there will be changes in specific structures deep within the brain that aid in the control and speed of movements.

Other neurological problems now known to occur in persons exposed to years of RHIs include cognitive impairment, behavioral changes, and amyotrophic lateral sclerosis (ALS). Understanding the frequency with which each of these happens remains a great scientific challenge.

Dr. Bottiglieri: When considering the risks of collision and injury to the brain, it may be more helpful to think under the broader category of neurodegenerative disease rather than focusing on just Parkinson’s. There is a clear association between repeated exposure to brain injury and neurodegenerative disease; we’ve known this since the 1920s, when doctors first defined dementia pugilistica in boxers, which is now known as CTE. If a person has some risk of neurodegenerative disease already, whether genetic or acquired, then repetitive head trauma can certainly increase the likelihood of developing it.

Dr. Noble: Contrary to what some people believe, the brain does not bounce around in the skull like a ball, but it does compress, expand, and twist, even against itself, on a microscopic level. These movements are very difficult to detect on conventional brain imaging or other tests, and most times do not cause a concussion. For most athletes in high-risk contact and collision sports, symptoms of concussion occur infrequently — maybe once among hundreds of meaningful hits to the head — but this exposure to RHIs still adds up over time.

The twisting and torquing on the brainstem or deep structures within the brain are thought to be responsible for symptoms of parkinsonism in people exposed to RHIs who don’t otherwise have a better explanation for their symptoms. The biggest challenge right now is that we don’t have good tools to determine the exact cause of parkinsonism. That can only be determined through direct examination of the brain after someone dies.

Dr. Bottiglieri: Some studies have suggested that the physiological changes related to minor traumatic brain injury, such as concussion in sport, persist even after clinical recovery from the injury. But even understanding the time to complete physical recovery from a physiological standpoint remains rather mysterious. We do not have a biomarker for concussion or a biomarker for recovery.

The other complicating factor is that sub-concussive trauma to the brain — the everyday collisions that do not manifest as concussions — chip away at the protective armor of the brain and are a cumulative concern for later-in-life degenerative disease, regardless of the number of concussions.

Dr. Bottiglieri: The brain has mechanisms for healing, but they are rather slow. The question as to whether we can prevent the scarring in brain that comes from inadequate healing and repetitive trauma is relatively unknown, but most experts agree that a rest interval after brain injury can allow time for some healing.

While sports organizations have concussion protocols, recovery can be more time-consuming than we think, so following those rules is the minimum you should do for a suspected concussion. Using techniques to reduce collisions and limiting the number of years playing collision sports can have a meaningful impact on protecting the brain. The goal should be limiting lifetime exposure to trauma.

Thomas S. Bottiglieri, DO, is a sports medicine physician with NewYork-Presbyterian/Columbia University Irving Medical Center and an assistant professor of sports medicine at Columbia University Vagelos College of Physicians and Surgeons. He specializes in the management of orthopedic injuries and disorders and is a nationally recognized expert and researcher in the field of concussion care.

James Noble, MD, MS, is a neurologist with NewYork-Presbyterian/Columbia University Irving Medical Center and an associate professor of neurology at Columbia University Vagelos College of Physicians and Surgeons. He primarily sees patients with dementia but is also involved in multidisciplinary clinical and research efforts to support patients with persistent post-concussive symptoms. Dr. Noble is the co-editor of the 14th edition of Merritt’s Neurology, a standard global neurology textbook, and has previously worked with the engineering department at Columbia University to develop technology to better diagnose concussions.