Ask the Doctors by Eve Glazier, M.D. and Elizabeth Ko, M.D

Researchers Still Studying Link Between TBI and Parkinson's

Dear Doctor: I had several concussions when I was younger due to various sports activities, not to mention one singularly bad bike ride. Now I read that a single concussion can raise the risk of Parkinson's disease. Just how serious is this increase in risk, and should I be worried?

Dear Reader: Your concern is understandable. The association between severe and moderate traumatic brain injury and Parkinson's has been recognized for some time.

Severe traumatic brain injury is an injury that leads to a loss of consciousness or coma that lasts for more than 24 hours and is evident on a brain imaging test. Moderate traumatic brain injury leads to a loss of consciousness for one to 24 hours and is evident via imaging. What you're describing sounds more like mild traumatic brain injury, in which the loss of consciousness lasts from seconds to minutes and brain imaging studies don't reveal brain injury. The majority of people describe this as a concussion. The question posed by the study you reference is whether mild traumatic brain injury can lead to Parkinson's disease.

The study looked at data from the Veterans Health Administration database. Researchers first gathered data on 162,935 veterans with a history of TBI and 162,935 veterans with no such history; they then classified the injury as mild, moderate or severe. The average age of both groups was about 48, and the veterans were followed for 4.64 years on average.

Overall, veterans with traumatic brain injury had a 71 percent relative increase in the risk of Parkinson's disease compared to those without TBI. The veterans with moderate or severe TBI had an 83 percent greater risk of Parkinson's, while those with mild TBI had a 56 percent relative increase in risk. When the authors looked further at those with mild TBI who had no loss of consciousness, they still found a 33 percent risk of Parkinson's. However, this last data point wasn't considered significant due to the low number of people diagnosed with Parkinson's in this group. Of note is that people with TBI had greater rates of psychiatric disorders.

Now let's look at why traumatic brain injury would lead to Parkinson's disease -- and let's start with Lewy bodies. These abnormal accumulations of protein in the brain have been known to contribute to Parkinson's, and a component of these proteins, called alpha-synuclein, is seen in the cerebrospinal fluid of those who have had severe traumatic brain injury. In addition, autopsy studies have found an association between early-life traumatic brain injury and Lewy bodies in the brain.

This is an important study for veterans. Of the 20 million veterans alive today, an estimated 40 percent have some history of TBI and 82 percent of those are considered mild TBI.

That brings us back to you and the concussions you had in sports and the biking accident. Although the study showed a 56 percent relative increased risk of Parkinson's with mild TBI, let us think of this another way. After the age of 60, Parkinson's affects 1 in 100 people, so if we extrapolate the data for those with mild TBI, the rate of Parkinson's would go up only to 1.56 in 100 people.

Still, it's good to understand the association between TBI and Parkinson's because it may lead to earlier recognition and treatment of the disease. But no one should panic just yet over the risk of Parkinson's caused by prior traumatic brain injuries.

(Send your questions to, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)