, according to a cross-sectional study published online Aug. 5 in JAMA Neurology.
The study of older, deceased former American football players with CTE showed that more years of play were associated with more severe white matter rarefaction and greater burden of neurofibrillary tau tangles in the dorsolateral frontal cortex, wrote Michael L. Alosco, PhD, assistant professor of neurology at Boston University’s CTE Center, and colleagues.
An analysis of donated brains
Repetitive head impacts are associated with CTE. The clinical presentation of CTE includes cognitive, behavioral, and mood changes that can progress to dementia. The contributions of pathologic changes in phosphorylated tau, white matter degeneration, and cerebrovascular disease to dementia in the context of CTE are poorly understood. Dr. Alosco and colleagues examined arteriosclerosis, infarcts, microinfarcts, microbleeds, and white matter rarefaction in donated brains to illuminate these contributions.
The researchers examined data from the Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) Study and Veterans Affairs–Boston University–Concussion Legacy Foundation. The population included deceased men who had played football and had received a neuropathologic diagnosis of CTE. Eligible participants had a history of repetitive head impacts. Brains that had been donated after a prolonged time postmortem and those with poor tissue quality were excluded.
Neuropathologists blinded to clinical data analyzed patients’ CTE stage and severity of neurofibrillary tangle burden in the dorsolateral frontal cortex as semiquantitative scales of phosphorylated tau severity. Neurofibrillary tangle burden was dichotomized as none or mild versus moderate or severe. The neuropathologists also rated white matter rarefaction and arteriolosclerosis severity using a scale of 0 points (i.e., none) to 3 points (i.e., severe changes). The investigators obtained clinical data through online surveys and retrospective telephone interviews with informants. They adjudicated consensus diagnoses of dementia based on modified criteria from DSM-IV.
White matter rarefaction was common
Dr. Alosco and colleagues included 180 individuals in their analysis, excluding those aged younger than 40 years because of low pathologic burden and minimal presence of dementia. Mean age at death was nearly 68 years. Fifty patients had no or mild neurofibrillary tangle burden, and 130 had moderate to severe burden. Thirty-five patients had CTE at stage I or II, and 145 had CTE at stage III or IV. In all, 120 patients were determined to have had dementia. About 47% of the sample had moderate to severe white matter rarefaction, and about 47% had arteriolosclerosis. Infarcts, microinfarcts, and microbleeds were uncommon.
When the investigators created a simultaneous equations regression model and controlled for age and race, they found that more years of play was associated with more severe white matter rarefaction, greater phosphorylated tau accumulation, and high CTE stage. Furthermore, white matter rarefaction and dorsolateral frontal cortex neurofibrillary tangles were associated with dementia. The association of years of play with dementia was mediated by white matter rarefaction and neurofibrillary tangle burden. Arteriolosclerosis was not associated with years of play, but arteriolosclerosis was independently associated with dementia.
The odds ratio for dementia was 1.69 among participants with more severe white matter rarefaction and 1.81 among patients with arteriolosclerosis. After the researchers controlled for age and race, the odds ratio of dementia was 2.65 among participants with a high neurofibrillary tangle burden, compared with participants with a low burden.
“Studies that include direct cardiovascular disease and repetitive head impacts metrics and refined measures of white matter integrity are needed to improve understanding of the pathogenesis of white matter rarefaction and cerebral small vessel changes in CTE,” Dr. Alosco and colleagues wrote.
The study was funded by grants from the National Institute on Aging, National Institute of Neurological Disorders and Stroke, the Department of Veterans Affairs, the Nick and Lynn Buoniconti Foundation, and the National Center for Advancing Translational Sciences. Some of the authors reported financial ties to the pharmaceutical industry and serving on professional sports committees.
SOURCE: Alosco ML et al. JAMA Neurol. 2019 Aug 5. doi: 10.1001/jamaneurol.2019.2244.