Repeated blows to the head, common in sports like boxing and mixed martial arts (MMA), may quietly disrupt the brain's waste-clearing system, according to a new study. The research, scheduled to be presented at the Radiological Society of North America (RSNA) annual meeting, examined the brains of cognitively impaired professional fighters and found evidence that the glymphatic system, responsible for flushing out toxins, weakens after sustained head impacts.
Sports-related traumatic brain injuries account for a significant portion of all brain injury cases, with boxing and MMA contributing substantially. While the link between repeated head trauma and neurodegenerative or neuropsychiatric conditions is well-established, this study sheds light on the potential mechanisms at play.
Understanding the Glymphatic System
The glymphatic system is a network of fluid-filled channels that act as the brain's waste disposal system, similar to the lymphatic system in the body. "The recently discovered glymphatic system is like the brain's plumbing and garbage disposal system," explained Dr. Dhanush Amin, the study's lead author from the University of Alabama at Birmingham and Cleveland Clinic Nevada. "It's vital for helping the brain flush out metabolites and toxins."
Researchers used diffusion tensor imaging along the perivascular space (DTI-ALPS), a specialized MRI technique, to measure water movement in and around the channels linked to glymphatic flow. These pathways are crucial for maintaining fluid balance, delivering nutrients and immune cells, and protecting against injury.
MRI Biomarkers and Brain Health
The DTI-derived ALPS index serves as a non-invasive marker of glymphatic function. Lower ALPS values indicate potential cognitive decline and have been associated with conditions like Alzheimer's and Parkinson's disease.
"When this system doesn't work properly, damaging proteins can accumulate, which have been linked to Alzheimer's and other forms of dementia," said Dr. Amin, now an assistant professor of neuroradiology at the University of Arkansas for Medical Sciences. "Studying this system gives us a new window into understanding and possibly slowing memory loss."
Study Details and Unexpected Findings
The study drew data from the Cleveland Clinic's Professional Athletes Brain Health Study (PABHS), which monitors around 900 active fighters. Researchers evaluated data from 280 athletes, including 95 with cognitive impairment at the study's outset, and compared them to 20 healthy controls.
Using the DTI-ALPS technique, researchers evaluated glymphatic activity and its relationship to the number of knockouts each athlete had experienced. They anticipated that impaired fighters would have lower ALPS values compared to those without impairment and that ALPS measurements would correlate with the number of knockouts.
However, the results were surprising. Impaired athletes initially showed higher glymphatic index values, but these values decreased significantly over time as the number of knockouts increased. Glymphatic function continued to decline in fighters who experienced ongoing head trauma.
"We believe that the glymphatic index was initially high in the impaired athlete group because the brain initially responds to repeated head injuries by ramping up its cleaning mechanism, but eventually, it becomes overwhelmed," Dr. Amin explained. "After a certain point, the brain just gives up."
The study also revealed that athletes without cognitive impairment had lower right-sided and overall glymphatic index values than impaired fighters, with a different pattern of glymphatic activity related to knockout history between the two groups.
Implications for Athlete Brain Health
Dr. Amin emphasized the importance of understanding how repeated head impacts affect the glymphatic system for early identification of neurodegenerative risk in contact sports athletes.
"If we can spot glymphatic changes in the fighters before they develop symptoms, then we might be able to recommend rest or medical care or help them make career decisions to protect their future brain health," he said.
