according to research published online ahead of print April 10 in the New England Journal of Medicine. The distribution of tau in the players’ brains appears to be similar to that in persons with chronic traumatic encephalopathy (CTE).
CTE is a neurodegenerative disease that has been associated with a history of repetitive head impacts, such as those withstood in contact sports. The basis for the neuropathological diagnosis of CTE is a distinct pattern of tau deposition with minimal deposition of amyloid-beta. Paired helical filament tau aggregates are first observed in the frontal, temporal, and parietal cortices. They later spread throughout the cerebral cortex, medial temporal lobe, diencephalon, and brainstem. CTE is diagnosed only through post mortem neuropathological examinations.
To examine whether tau and amyloid deposition can be detected in the brains of living people at risk for CTE, Robert A. Stern, PhD, and his colleagues studied living former NFL players and asymptomatic controls with flortaucipir PET (to detect tau) and 18F-florbetapir PET (to detect amyloid-beta). Dr. Stern is director of clinical research at the CTE Center at Boston University. Eligible former players were male, aged 40-69 years, had played football in the NFL for at least 2 years, had had at least 12 years of total tackle football experience, and reported cognitive, behavioral, and mood symptoms through telephone screening. Eligible controls were male, aged 40-69 years, and had no cognitive symptoms or history of traumatic brain injury.
All subjects underwent flortaucipir PET, florbetapir PET, and T1-weighted volumetric MRI of the head. Dr. Stern and his colleagues used automated image-analysis algorithms to compare the regional tau standardized uptake value ratio (SUVR) between the two patient groups and to evaluate potential associations between that ratio and symptom severity or years of football play.
The investigators included 26 former players and 31 controls in their analysis. The group of former players had a higher percentage of black participants and a lower mean Mini-Mental State Examination score, compared with controls. The mean flortaucipir SUVR was higher among former players than among controls in the bilateral superior frontal (1.09 vs. 0.98), bilateral medial temporal (1.23 vs. 1.12), and left parietal (1.12 vs. 1.01) regions. Dr. Stern and his colleagues found no association between tau deposition in those regions and results on cognitive and neuropsychiatric tests. In a post hoc analysis, they calculated the correlation coefficients in the three brain regions between the SUVRs and years of play to be 0.58 in the bilateral superior frontal region, 0.45 in the bilateral medial temporal region, and 0.50 in the left parietal region. Mean cortical:cerebellar florbetapir SUVRs did not differ significantly between groups.
“These findings suggest that the cognitive difficulties reported by the former players were not related to Alzheimer’s disease amyloid-beta deposition,” said the authors. The study may have been insufficiently powered to detect associations between flortaucipir uptake and the clinical measures, they added. Also, paired helical filament tau pathology alone may not be associated with the former players’ neuropsychiatric symptoms and cognitive impairment. “Although this study showed between-group differences in flortaucipir PET measurements, our analyses do not pertain to detection of tau pathology in individual participants,” the authors concluded.
The study was supported by an investigator-initiated grant from Avid Radiopharmaceuticals. The National Institutes of Health, the state of Arizona, and the U.S. Department of Defense also supported the study.
SOURCE: Stern RA et al. N Engl J Med. 2019 Apr 10. doi: 10.1056/NEJMoa1900757 (Epub ahead of print).