Bridging Trauma and Parkinson's Disease: Mechanisms, Models, and Biomarkers of Post-Traumatic Parkinsonism.

One of the most prevalent neurodegenerative diseases, Parkinson's disease (PD), is generally discussed in terms of aging, genetic predisposition, and environmental exposures. Nonetheless, there is growing evidence that both isolated severe traumatic events and repetitive mild traumatic brain injury may play a significant role in the development of parkinsonian features. This trauma-associated condition, known as Post-Traumatic Parkinsonism Syndrome (PTPS), is becoming more widely acknowledged as a clinically significant but underdiagnosed illness. The differences between PTPS and conditions like chronic traumatic encephalopathy (CTE) are often blurred because, in contrast to idiopathic PD, PTPS typically manifests after a specified latency period following head injury and is often accompanied by overlapping symptoms of cognitive, behavioral, and motor dysfunction. At the pathophysiological level, PTPS is defined by the combination of trauma-induced processes, such as neuroinflammation, axonal injury, and dysregulated acetylation pathways, with mechanisms known to be associated with PD, such as alpha-synuclein aggregation, dopaminergic neuronal loss, and impaired protein clearance. Today, experimental models demonstrate how trauma speeds up or even starts neurodegenerative cascades, providing a unique platform to investigate disease mechanisms outside of the traditional toxin-based paradigms of PD. The current understanding of PD, PTPS, and CTE is summarized in this review, with a focus on risk factors, comparative pathology, and experimental model translational insights. This review emphasizes the significance of acknowledging trauma as more than a trigger but rather as a potential contributor to long-term neurodegeneration and disability by presenting PTPS as a unique but related syndrome within the PD spectrum.