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Clinical Topics

Even Mild TBI Can Dramatically Increase Risk of Developing Parkinson’s Disease

by Brenda Mooney

August 4, 2018

SAN FRANCISCO — Mild traumatic brain injury, commonly known as concussion, appears to increase a patient’s risk of developing Parkinson’s disease by as much as 56%, a new veterans study found.

That is of significant concern to federal medicine, because nearly 380,000 servicemembers have been diagnosed with mTBI since 2000, according to DoD statistics.

Parkinson’s disease is a chronic, neurological disease caused by a loss of dopamine-producing cells in the brain and is treatable but not curable. Classic motor symptoms include tremor during rest, stiff limbs, slowness of movement and gait-and- balance problems that progress over time, while nonmotor symptoms, such as sleep disturbances, urinary dysfunction, constipation, swallowing problems, mood disorders and cognitive deficits also can occur.

The recent study was published in the journal Neurology. “Previous research has shown a strong link between moderate to severe traumatic brain injury and an increased risk of developing Parkinson’s disease, but the research on mild traumatic brain injury has not been conclusive,” pointed out senior study author Kristine Yaffe, MD, of the San Francisco VAMC and the University of California, San Francisco. “Our research looked a very large population of U.S. veterans who had experienced either mild, moderate or severe traumatic brain injury in an effort to find an answer to whether a mild traumatic brain injury can put someone at risk.”

For purposes of the study, moderate to severe traumatic brain injury was defined as a loss of consciousness for more than 30 minutes, alteration of consciousness of more than 24 hours or amnesia for more than 24 hours. On the other hand, mild traumatic brain injury was defined as loss of consciousness for 0 to 30 minutes, alteration of consciousness of a moment to 24 hours or amnesia for 0 to 24 hours.

Participants were 325,870 veterans from three VHA medical databases—half of the patients had been diagnosed with either a mild, moderate or severe TBI, and half had not. None of the participants, ranging in age from 31 to 65, had Parkinson’s disease or dementia at initiation of the retrospective cohort study.

Specifically, the study team identified all patients with a TBI diagnosis in VHA databases from October 2002 to September 2014 and age-matched them 1:1 to a random sample of patients without TBI. Brain injury exposure and severity were determined with detailed clinical assessments or ICD-9 codes using DoD and Veterans Brain Injury Center criteria. ICD-9 codes were employed to determine baseline comorbidities and incident PD more than one year post-TBI.

Risk Greater for More-Severe TBI

Patients, averaging 47.9 years old, were followed for an average of 4.6 years. Results indicated that 1,462 of the participants were diagnosed with Parkinson’s disease at least one year and up to 12 years after the start of the study, however, with 4.6 years being the average time to diagnosis.

More significant, according to the authors, was that 949 of the participants with TBI, 0.58%, developed Parkinson’s disease, compared to 513 of the participants with no brain injury at all, 0.31%.

A data breakdown demonstrated that 360 out of 76,297 patients with mild traumatic brain injury, 0.47%, and 543 out of 72,592 with moderate to severe traumatic brain injury, 0.75 percent, developed Parkinson’s disease.

Researchers adjusted the results for age, sex, race and education, as well as chronic conditions such as diabetes and hypertension. Results showed that veterans with any level of traumatic brain injury had a 71% increased risk of Parkinson’s disease. While the risk was greater for those with moderate to severe traumatic brain injury at an 83% increase, it still was significant for mTBI at a 56% increase.

Being diagnosed with any type of TBI also appeared to increase the likelihood of an earlier Parkinson’s diagnosis by two years, the study noted.

The Defense and Veterans Brain Injury Center noted that active duty and reserve servicemembers are at much greater risk of suffering TBI than civilians for several reasons, including demographics. In all settings, young men between the ages of 18 to 24 are at greatest risk. In addition, the DVBIC stated on its website “many operational and training activities, which are routine in the military, are physically demanding and even potentially dangerous. Military servicemembers are increasingly deployed to areas where they are at risk for experiencing blast exposures from improvised explosive devices, suicide bombers, land mines, mortar rounds and rocket-propelled grenades.”

Not all of the injuries are combat-related, however. The DVBIC pointed out that “TBI is not uncommon, even in garrison, and can occur during usual daily activities.” Activities such as riding motorcycles, climbing mountains and parachuting from planes for recreation increase the risk. So can physical training, which is an integral part of the active duty servicemember’s everyday life, according to the group.

Authors of the Neurology study suggested some solutions.

Author Raquel C. Gardner, MD, of the San Francisco VAMC and the University of California, San Francisco.

“This study highlights the importance of concussion prevention, long-term follow-up of those with concussion and the need for future studies to investigate if there are other risk factors for Parkinson’s disease that can be modified after someone has a concussion,” explained lead author Raquel C. Gardner, MD, also of the San Francisco VAMC and the University of California, San Francisco. “While our study looked at veterans, we believe the results may have important implications for athletes and the general public, as well.”

Study authors said that a limitation of the study was that medical codes were used to identify people with TBI and might have been missed in some cases. They also emphasized that the problem could be greater than suspected, because mTBI is likely to have been underreported in those serving in combat.


1Gardner RC, Byers AL, Barnes DE, Li Y, Boscardin J, Yaffe K. Mild TBI and risk of Parkinson disease: A Chronic Effects of Neurotrauma Consortium Study. Neurology. 2018 May 15;90(20):e1771-e1779. doi: 10.1212/WNL.0000000000005522. Epub 2018 Apr 18. PubMed PMID: 29669907; PubMed Central PMCID: PMC5957305.

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