Under the glow of the arena lights, the two combatants square off. For professional fighters, such as boxers and mixed martial artists, traumatic brain injuries are an occupational hazard. But repeated head trauma, even ones that don’t result in a knockout, can pack a punch against the brain and are a risk factor for neuro-degenerative and psychiatric conditions.
In the brain, the glymphatic system acts like the brain’s plumbing and garbage disposal, clearing out waste products. However, worsened function of this system can clog the brain with accumulated proteins, which have been linked to Alzheimer's disease and other forms of dementia.
This motivated researchers like Dhanush Amin, a neuroradiologist at the University of Arkansas for Medical Sciences, to study this system in greater depth. The team will present their new findings at the annual meeting of the Radiological Society of North America. They found that glymphatic system function significantly declines with repeated head impacts in cognitively impaired fighters. “Studying this system gives us a new window into understanding and possibly slowing memory loss,” said Amin in a statement.
First, Amin and his colleagues analyzed data from a longitudinal study that included approximately 900 active fighters, wherein nearly 300 male professional boxers and mixed martial artists had been followed for at least three years. From this group, the researchers assessed 95 fighters who were cognitively impaired at baseline and 20 healthy controls.
Then, the researchers used a specialized MRI technique called diffusion tensor imaging along the perivascular space (DTI-ALPS). This measured and analyzed water movement in and around the spaces that surround the channels of the glymphatic system. From this, they calculated the DTI-derived ALPS index, which is a non-invasive biomarker that assesses glymphatic function. An impaired, or lower, DTI-ALPS index can be a marker for cognitive decline and is associated with the progression of conditions like Alzheimer’s and Parkinson’s disease.
So, the researchers hypothesized that cognitively impaired fighters would have a lower glymphatic index compared to non-impaired fighters. However, contrary to their initial hypothesis, the impaired fighters had a significantly higher index compared to healthy controls.
“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,” Amin explained in the press release. “After a certain point, the brain just gives up.”
When the researchers looked at the correlation between the glymphatic index and the total number of knockouts the fighters experienced, they observed a negative correlation in the impaired fighter group. Notably, the athletes with continued brain trauma had worsened glymphatic function over time.
From this work, Amin noted that, “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.”
