Athletes who sustained repetitive head impacts through contact sports for several years had an increased risk for neurodegenerative diseases, including Lewy body disease (LBD), which in turn, can cause symptoms of Parkinson's disease and dementia, according to the findings of a study published in the Journal of Neuropathology and Experimental Neurology on September 1.
A 2016 study published in JAMA Neurology found a link between traumatic brain injuries (TBIs) with a loss of consciousness and an increased risk for Lewy bodies. LBD, which is linked to dementia and Parkinson's disease, is caused by abnormal deposits of Alpha-synuclein. CTE and LBD can occur simultaneously, but it's unclear whether CTE pathology influences the likelihood of developing LBD.
To test whether contact sports and CTE are associated with LBD, a team of researchers studied 654 brains from three repositories: 269 came from the “Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE)” study at the Veteran’s Affairs-Boston University-Concussion Legacy Foundation (VA-BU-CLF) brain bank (UNITE group); 261 were from Boston University’s Alzheimer Disease Center (ADC); and 164 were from the brain bank of the Framingham Heart Study (FHS), which is a community-based aging cohort study.
Through interviews with next of kin, online surveys, and reviews of medical records, the researchers were able to assess history of repetitive head impacts, athletic or military service history, history of cognitive, mood, and behavior changes, and clinical status leading up to death in UNITE participants. For FHS participants, the researchers characterized repetitive exposure and athletic history by the total number of years the athlete played contact sports. No athletic history was available in the ADC cohort.
Through interviews with a panel of neurologists and neuropsychologists, reviews of medical and study records, and evaluation of the brains, the researchers were able to assess repetitive head impacts and neurodegenerative diseases, the presence or absence of dementia, parkinsonism, and CTE.
The researchers found that athletes who played more than eight years of contact sports had more than six times the risk of developing neocortical (diffuse) LBD, a type of LBD in the brain's cortex, compared to those who played eight years or fewer, regardless of whether they had a history of CTE. They did not find a link between CTE and LBD, except that they both involve repetitive head impacts.
"Lewy body pathology appears to involve similar regions in CTE as in LBD alone," the researchers wrote.
Dementia was found to be significantly associated with neocortical LBD, CTE stage, and Alzheimer's disease; parkinsonism was linked with LBD pathology, but not CTE stage. Participants with both CTE and LBD were more likely to have dementia and symptoms of Parkinson's disease than those with CTE pathology alone.
The researchers stressed participants in the UNITE study are not representative of all people who play contact sports or sustain repetitive head injuries. The brains were mostly self-selected or referred by next-of-kin after death.
The findings warrant further research to better determine the risks associated with repetitive head impacts and neurodegeneration.