Can a Past Brain Injury Cause Parkinson's? What the VA Data Shows
Someone asked me this week if a brain injury from years ago could actually cause Parkinson's disease. She's a veteran, fully disabled, and she wanted a real answer, not a guess. Here's what the research actually shows.
The VA study
In 2018, researchers published a study in the journal Neurology that followed 325,870 veterans through VA medical records, half of whom had a documented traumatic brain injury, half of whom didn't. None of them had Parkinson's at the start. Over an average of four and a half years, the researchers tracked who developed it.
Veterans with a mild traumatic brain injury had a 56 percent higher risk of developing Parkinson's than veterans with no TBI history. Veterans with a moderate to severe traumatic brain injury had an 83 percent higher risk. The lead researcher, Dr. Kristine Yaffe of UCSF, said her team expected the moderate to severe group to carry more risk. What surprised them was how much risk the mild TBI group carried too.
It's not just veterans
A Danish national study using hospital records found a similar pattern outside the veteran population entirely, so this isn't specific to combat exposure or blast injuries. Head injury itself appears to be the common thread.
Even with that increased risk, Parkinson's after TBI is still uncommon in absolute terms. Less than 1 percent of veterans in the VA study developed Parkinson's at all, with or without a brain injury. A past TBI raises the odds. It does not make the outcome likely.
What's happening in the brain
Researchers point to a few overlapping mechanisms. TBI can trigger chronic inflammation in brain tissue that doesn't fully resolve after the injury heals. It can also promote misfolding of a protein called alpha-synuclein, the same protein that clumps together and damages neurons in Parkinson's disease itself. Some studies have found signs of this kind of protein buildup in brain tissue examined after TBI, concentrated in the substantia nigra, the same region where Parkinson's causes its characteristic loss of dopamine-producing neurons.
A separate condition worth knowing
There's also a second, separate condition called post-traumatic parkinsonism. This is not the same as a Parkinson's disease diagnosis. It tends to follow a more severe injury that directly damages the basal ganglia, the deep brain structures involved in movement control. It shows the same core symptoms, slowness of movement, rigidity, tremor, but on a different timeline and through a different mechanism. Most people who develop it do so within six months of the injury, most often after a motor vehicle accident or a fall.
What to actually do
If you're a veteran with a documented TBI in your record and you're noticing new tremor, stiffness, slowness, or balance changes, bring that to a neurologist directly, and name the TBI history when you do. Don't assume a doctor will automatically connect a head injury from fifteen years ago to a movement symptom showing up today unless you raise it yourself.
A traumatic brain injury does not guarantee Parkinson's disease. But it is a documented, measurable risk factor, not a myth, not a stretch, and not something to brush off if you're the one living with that history.
References
Gardner RC, Burke JF, Nettiksimmons J, Goldman S, Tanner CM, Yaffe K. "Traumatic brain injury in later life increases risk for Parkinson disease." Neurology, 2018.
Kenborg L, Rugbjerg K, et al. "Head injury and risk for Parkinson disease: results from a Danish case-control study." Neurology, 2015.
Delic V, et al. "Biological links between traumatic brain injury and Parkinson's disease." Acta Neuropathologica Communications, 2020.
Rojvirat C, et al. "Systematic review of post-traumatic parkinsonism." Neurotrauma Reports, 2024.
