Characterizing tau deposition in chronic traumatic encephalopathy (CTE): utility of the McKee CTE staging scheme

Chronic traumatic encephalopathy (CTE) is a tauopathy associated with repetitive head impacts (RHI) that has been neuropathologically diagnosed in American football players and other contact sport athletes. In 2013, McKee and colleagues proposed a staging scheme for characterizing the severity of the hyperphosphorylated tau (p-tau) pathology, the McKee CTE staging scheme. The staging scheme defined four pathological stages of CTE, stages I(mild)-IV(severe), based on the density and regional deposition of p-tau. The objective of this study was to test the utility of the McKee CTE staging scheme, and provide a detailed examination of the regional distribution of p-tau in CTE. We examined the relationship between the McKee CTE staging scheme and semi-quantitative and quantitative assessments of regional p-tau pathology, age at death, dementia, and years of American football play among 366 male brain donors neuropathologically diagnosed with CTE (mean age 61.86, SD 18.90). Spearman's rho correlations showed that higher CTE stage was associated with higher scores on all semi-quantitative and quantitative assessments of p-tau severity and density (p's < 0.001). The severity and distribution of CTE p-tau followed an age-dependent progression: older age was associated with increased odds for having a higher CTE stage (p < 0.001). CTE stage was independently associated with increased odds for dementia (p < 0.001). K-medoids cluster analysis of the semi-quantitative scales of p-tau across 14 regions identified 5 clusters of p-tau that conformed to increasing CTE stage (stage IV had 2 slightly different clusters), age at death, dementia, and years of American football play. There was a predilection for p-tau pathology in five regions: dorsolateral frontal cortex (DLF), superior temporal cortex, entorhinal cortex, amygdala, and locus coeruleus (LC), with CTE in the youngest brain donors and lowest CTE stage restricted to DLF and LC. These findings support the usefulness of the McKee CTE staging scheme and demonstrate the regional distribution of p-tau in CTE.

A magnetic resonance spectroscopy investigation in symptomatic former NFL players

The long-term neurologic consequences of exposure to repetitive head impacts (RHI) are not well understood. This study used magnetic resonance spectroscopy (MRS) to examine later-life neurochemistry and its association with RHI and clinical function in former National Football League (NFL) players. The sample included 77 symptomatic former NFL players and 23 asymptomatic individuals without a head trauma history. Participants completed cognitive, behavior, and mood measures. N-acetyl aspartate, glutamate/glutamine, choline, myo-inositol, creatine, and glutathione were measured in the posterior (PCG) and anterior (ACG) cingulate gyrus, and parietal white matter (PWM). A cumulative head impact index (CHII) estimated RHI. In former NFL players, a higher CHII correlated with lower PWM creatine (r = -0.23, p = 0.02). Multivariate mixed-effect models examined neurochemical differences between the former NFL players and asymptomatic individuals without a history of head trauma. PWM N-acetyl aspartate was lower among the former NFL players (mean diff. = 1.02, p = 0.03). Between-group analyses are preliminary as groups were recruited based on symptomatic status. The ACG was the only region associated with clinical function, including positive correlations between glutamate (r = 0.32, p = 0.004), glutathione (r = 0.29, p = 0.02), and myo-inositol (r = 0.26, p = 0.01) with behavioral/mood symptoms. Other positive correlations between ACG neurochemistry and clinical function emerged (i.e., behavioral/mood symptoms, cognition), but the positive directionality was unexpected. All analyses controlled for age, body mass index, and education (for analyses examining clinical function). In this sample of symptomatic former NFL players, there was a direct effect between RHI and reduced cellular energy metabolism (i.e., lower creatine). MRS neurochemicals associated with neuroinflammation also correlated with behavioral/mood symptoms.

Clinical Presentation of Chronic Traumatic Encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive head impacts (RHI), such as those received in contact/collision sports, blast injury in military veterans, and domestic violence. Currently, CTE can only be diagnosed following death. Although the clinical features of former boxers have been described for almost a century, and there is increasing evidence of long-term cognitive and neuropsychiatric impairments in living former American football players, the specific clinical presentation associated with underlying CTE neuropathology remains unclear. These features include diverse and nonspecific changes in cognition, mood, behavior, and motor functioning. Currently, there are no validated and widely accepted clinical diagnostic criteria. Proposed criteria are primarily based on retrospective telephonic interviews with the next of kin of individuals who were diagnosed with CTE postmortem. Prospective studies involving individuals presumably at high risk for CTE are underway; these will hopefully clarify the clinical features and course of CTE, allow the diagnostic criteria to be refined, and lead to the development and validation of in vivo biomarkers. This article reviews what is currently known about the clinical presentation of CTE and describes the evolution of this knowledge from early case reports of "punch drunk" boxers through larger case series of neuropathologically confirmed CTE. This article concludes with a discussion of gaps in research and future directions to address these areas.

Risk Factors for Chronic Traumatic Encephalopathy: A Proposed Framework

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disease that has been neuropathologically diagnosed in contact and collision sport athletes, military veterans, and others with a history of exposure to repetitive head impacts (RHI). Identifying methods to diagnose and prevent CTE during life is a high priority. Timely diagnosis and implementation of treatment and preventative strategies for neurodegenerative diseases, including CTE, partially hinge upon early and accurate risk characterization. Here, we propose a framework of risk factors that influence the neuropathological development of CTE. We provide an up-to-date review of the literature examining cumulative exposure to RHI as the environmental trigger for CTE. Because not all individuals exposed to RHI develop CTE, the direct and/or indirect influence of nonhead trauma exposure characteristics (e.g., age, sex, race, genetics) on the pathological development of CTE is reviewed. We conclude with recommendations for future directions, as well as opinions for preventative strategies that could mitigate risk.

Evolution of neuronal and glial tau isoforms in chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative tauopathy characterized by accumulation of hyperphosphorylated tau (p-tau) in perivascular aggregates in neurons and glia at the depths of neocortical sulci and progresses to diffuse neocortical, allocortical and brainstem structures. The strongest risk factor is exposure to repetitive head impacts acquired most commonly through contact sports and military service. Given that CTE can only be definitively diagnosed after death, a better understanding of the cellular and molecular changes in CTE brains may lead to identification of mechanisms that could be used for novel biomarkers, monitoring progression or therapeutic development. Disruption of alternative pre-mRNA splicing of tau mRNA plays a pathogenic role in tauopathy, with multiple characteristic patterns of isoform accumulation varying among tauopathies. Limited data are available on CTE, particularly at early stages. Using biochemical and histological approaches, we performed a detailed characterization of tau isoform signatures in post-mortem human brain tissue from individuals with a range of CTE stages (n = 99). In immunoblot analyses, severity was associated with decreased total monomeric tau and increased total oligomeric tau. Immunoblot with isoform-specific antisera revealed that oligomeric tau with three and four microtubule binding domain repeats (3R and 4R) also increased with CTE severity. Similarly, immunohistochemical studies revealed p-tau accumulation consisting of both 3R and 4R in perivascular lesions. When the ratio of 4R:3R was analyzed, there was mixed expression throughout CTE stages, although 4R predominated in early CTE stages (I-II), a 3R shift was observed in later stages (III-IV). While neurons were found to contain both 3R and 4R, astrocytes only contained 4R. These 4R-positive cells were exclusively neuronal at early stages. Overall, these findings demonstrate that CTE is a mixed 4R/3R tauopathy. Furthermore, histologic analysis reveals a progressive shift in tau isoforms that correlates with CTE stage and extent of neuronal pathology.

Late contributions of repetitive head impacts and TBI to depression symptoms and cognition

OBJECTIVE

To test the hypothesis that repetitive head impacts (RHIs), like those from contact sport play and traumatic brain injury (TBI) have long-term neuropsychiatric and cognitive consequences, we compared middle-age and older adult participants who reported a history of RHI and/or TBI with those without this history on measures of depression and cognition.

METHODS

This cross-sectional study included 13,323 individuals (mean age, 61.95; 72.5% female) from the Brain Health Registry who completed online assessments, including the Ohio State University TBI Identification Method, the Geriatric Depression Scale (GDS-15), and the CogState Brief Battery and Lumos Labs NeuroCognitive Performance Tests. Inverse propensity-weighted linear regressions accounting for age, sex, race/ethnicity, and education tested the effects of RHI and TBI compared to a non-RHI/TBI group.

RESULTS

A total of 725 participants reported RHI exposure (mostly contact sport play and abuse) and 7,277 reported TBI (n = 2,604 with loss of consciousness [LOC]). RHI (β, 1.24; 95% CI, 0.36-2.12), TBI without LOC (β, 0.43; 95% CI, 0.31-0.54), and TBI with LOC (β, 0.75; 95% CI, 0.59-0.91) corresponded to higher GDS-15 scores. While TBI with LOC had the most neuropsychological associations, TBI without LOC had a negative effect on CogState Identification (β, 0.004; 95% CI, 0.001-0.01) and CogState One Back Test (β, 0.004; 95% CI, 0.0002-0.01). RHI predicted worse CogState One Back Test scores (β, 0.02; 95% CI, -0.01 to 0.05). There were RHI × TBI interaction effects on several neuropsychological subtests, and participants who had a history of both RHI and TBI with LOC had the greatest depression symptoms and worse cognition.

CONCLUSIONS

RHI and TBI independently contributed to worse mid- to later-life neuropsychiatric and cognitive functioning.

A longitudinal examination of plasma neurofilament light and total tau for the clinical detection and monitoring of Alzheimer's disease

We examined baseline and longitudinal associations between plasma neurofilament light (NfL) and total tau (t-tau), and the clinical presentation of Alzheimer's disease (AD). A total of 579 participants (238, normal cognition [NC]; 185, mild cognitive impairment [MCI]; 156, AD dementia) had baseline blood draws; 82% had follow-up evaluations. Plasma samples were analyzed for NfL and t-tau using Simoa technology. Baseline plasma NfL was higher in AD dementia than MCI (standardized mean difference = 0.55, 95% CI: 0.37-0.73) and NC (standardized mean difference = 0.68, 95% CI: 0.49-0.88), corresponded to Clinical Dementia Rating scores (OR = 1.94, 95% CI: 1.35-2.79]), and correlated with all neuropsychological tests (r's = 0.13-0.42). Longitudinally, NfL did not predict diagnostic conversion but predicted decline on 3/10 neuropsychological tests. Baseline plasma t-tau was higher in AD dementia than NC with a small effect (standardized mean difference = 0.33, 95% CI: 0.10-0.57) but not MCI. t-tau did not statistically significant predict any longitudinal outcomes. Plasma NfL may be useful for the detection of AD dementia and monitoring of disease progression. In contrast, there was minimal evidence in support of plasma t-tau.

Hippocampal Resting-State Functional Connectivity Patterns are More Closely Associated with Severity of Subjective Memory Decline than Whole Hippocampal and Subfield Volumes

The goal of this study was to examine whether hippocampal volume or resting-state functional connectivity (rsFC) patterns are associated with subjective memory decline (SMD) in cognitively normal aged adults. Magnetic resonance imaging data from 53 participants (mean age: 71.9 years) of the Boston University Alzheimer’s Disease Center registry were used in this cross-sectional study. Separate analyses treating SMD as a binary and continuous variable were performed. Subfield volumes were generated using FreeSurfer v6.0, and rsFC strength between the head and body of the hippocampus and the rest of the brain was calculated. Decreased left whole hippocampal volume and weaker rsFC strength between the right body of the hippocampus and the default mode network (DMN) were found in SMD+. Cognitive Change Index score was not correlated with volumetric measures but was inversely correlated with rsFC strength between the right body of the hippocampus and 6 brain networks, including the DMN, task control, and attentional networks. These findings suggest that hippocampal rsFC patterns reflect the current state of SMD in cognitively normal adults and may reflect subtle memory changes that standard neuropsychological tests are unable to capture.

Duration of American Football Play and Chronic Traumatic Encephalopathy

OBJECTIVE

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to contact and collision sports, including American football. We hypothesized a dose-response relationship between duration of football played and CTE risk and severity.

METHODS

In a convenience sample of 266 deceased American football players from the Veterans Affairs-Boston University-Concussion Legacy Foundation and Framingham Heart Study Brain Banks, we estimated the association of years of football played with CTE pathological status and severity. We evaluated the ability of years played to classify CTE status using receiver operating characteristic curve analysis. Simulation analyses quantified conditions that might lead to selection bias.

RESULTS

In total, 223 of 266 participants met neuropathological diagnostic criteria for CTE. More years of football played were associated with having CTE (odds ratio [OR] = 1.30 per year played, 95% confidence interval [CI] = 1.19-1.41; p = 3.8 × 10-9 ) and with CTE severity (severe vs mild; OR = 1.14 per year played, 95% CI = 1.07-1.22; p = 3.1 × 10-4 ). Participants with CTE were 1/10th as likely to have played <4.5 years (negative likelihood ratio [LR] = 0.102, 95% CI = 0.100-0.105) and were 10 times as likely to have played >14.5 years (positive LR = 10.2, 95% CI = 9.8-10.7) compared with participants without CTE. Sensitivity and specificity were maximized at 11 years played. Simulation demonstrated that years played remained adversely associated with CTE status when years played and CTE status were both related to brain bank selection across widely ranging scenarios.

INTERPRETATION

The odds of CTE double every 2.6 years of football played. After accounting for brain bank selection, the magnitude of the relationship between years played and CTE status remained consistent. ANN NEUROL 2020;87:116-131.

Revised Framingham Stroke Risk Profile: Association with Cognitive Status and MRI-Derived Volumetric Measures

BACKGROUND

The Framingham Stroke Risk Profile (FSRP) was created in 1991 to estimate 10-year risk of stroke. It was revised in 2017 (rFSRP) to reflect the modern data on vascular risk factors and stroke risk.

OBJECTIVE

This study examined the association between the rFSRP and cognitive and brain aging outcomes among participants from the National Alzheimer's Coordinating Center (NACC) Uniform Data Set (UDS).

METHODS

Cross-sectional rFSRP was computed at baseline for 19,309 participants (mean age = 72.84, SD = 8.48) from the NACC-UDS [9,697 (50.2%) normal cognition, 4,705 (24.4%) MCI, 4,907 (25.4%) dementia]. Multivariable linear, logistic, or ordinal regressions examined the association between the rFSRP and diagnostic status, neuropsychological test performance, CDR® Sum of Boxes, as well as total brain volume (TBV), hippocampal volume (HCV), and log-transformed white matter hyperintensities (WMH) for an MRI subset (n = 1,196). Models controlled for age, sex, education, racial identity, APOEɛ4 status, and estimated intracranial volume for MRI models.

RESULTS

The mean rFSRP probability was 10.42% (min = 0.50%, max = 95.71%). Higher rFSRP scores corresponded to greater CDR Sum of Boxes (β= 0.02, p = 0.028) and worse performance on: Trail Making Test A (β= 0.05, p < 0.001) and B (β= 0.057, p < 0.001), and Digit Symbol (β= -0.058, p < 0.001). Higher rFSRP scores were associated with increased odds for a greater volume of log-transformed WMH (OR = 1.02 per quartile, p = 0.015). No associations were observed for diagnosis, episodic memory or language test scores, HCV, or TBV.

CONCLUSION

These results support the rFSRP as a useful metric to facilitate clinical research on the associations between cerebrovascular disease and cognitive and brain aging.

Interactive Effects of Racial Identity and Repetitive Head Impacts on Cognitive Function, Structural MRI-Derived Volumetric Measures, and Cerebrospinal Fluid Tau and Aβ

BACKGROUND

Factors of increased prevalence among individuals with Black racial identity (e.g., cardiovascular disease, CVD) may influence the association between exposure to repetitive head impacts (RHI) from American football and later-life neurological outcomes. Here, we tested the interaction between racial identity and RHI on neurobehavioral outcomes, brain volumetric measures, and cerebrospinal fluid (CSF) total tau (t-tau), phosphorylated tau (p-tau181), and Aβ1 - 42 in symptomatic former National Football League (NFL) players.

METHODS

68 symptomatic male former NFL players (ages 40-69; n = 27 Black, n = 41 White) underwent neuropsychological testing, structural MRI, and lumbar puncture. FreeSurfer derived estimated intracranial volume (eICV), gray matter volume (GMV), white matter volume (WMV), subcortical GMV, hippocampal volume, and white matter (WM) hypointensities. Multivariate generalized linear models examined the main effects of racial identity and its interaction with a cumulative head impact index (CHII) on all outcomes. Age, years of education, Wide Range Achievement Test, Fourth Edition (WRAT-4) scores, CVD risk factors, and APOEε4 were included as covariates; eICV was included for MRI models. P-values were false discovery rate adjusted.

RESULTS

Compared to White former NFL players, Black participants were 4 years younger (p = 0.04), had lower WRAT-4 scores (mean difference = 8.03, p = 0.002), and a higher BMI (mean difference = 3.09, p = 0.01) and systolic blood pressure (mean difference = 8.15, p = 0.03). With regards to group differences on the basis of racial identity, compared to White former NFL players, Black participants had lower GMV (mean adjusted difference = 45649.00, p = 0.001), lower right hippocampal volume (mean adjusted difference = 271.96, p = 0.02), and higher p-tau181/t-tau ratio (mean adjusted difference = -0.25, p = 0.01). There was not a statistically significant association between the CHII with GMV, right hippocampal volume, or p-tau181/t-tau ratio. However, there was a statistically significant Race x CHII interaction for GMV (b = 2206.29, p = 0.001), right hippocampal volume (b = 12.07, p = 0.04), and p-tau181/t-tau ratio concentrations (b = -0.01, p = 0.004).

CONCLUSION

Continued research on racial neurological disparities could provide insight into risk factors for long-term neurological disorders associated with American football play.

Association of White Matter Rarefaction, Arteriolosclerosis, and Tau With Dementia in Chronic Traumatic Encephalopathy

IMPORTANCE

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive head impacts, including those from US football, that presents with cognitive and neuropsychiatric disturbances that can progress to dementia. Pathways to dementia in CTE are unclear and likely involve tau and nontau pathologic conditions.

OBJECTIVE

To investigate the association of white matter rarefaction and cerebrovascular disease with dementia in deceased men older than 40 years who played football and had CTE.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study involves analyses of data from the ongoing Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) Study, which is conducted via and included brain donors from the Veterans Affairs-Boston University-Concussion Legacy Foundation brain bank between 2008 and 2017. An original sample of 224 men who had played football and were neuropathologically diagnosed with CTE was reduced after exclusion of those younger than 40 years and those missing data.

EXPOSURES

The number of years of football play as a proxy for repetitive head impacts.

MAIN OUTCOMES AND MEASURES

Neuropathological assessment of white matter rarefaction and arteriolosclerosis severity (on a scale of 0-3, where 3 is severe); number of infarcts, microinfarcts, and microbleeds; and phosphorylated tau accumulation determined by CTE stage and semiquantitative rating of dorsolateral frontal cortex (DLFC) neurofibrillary tangles (NFTs) (none or mild vs moderate or severe). Informant-based retrospective clinical interviews determined dementia diagnoses via diagnostic consensus conferences.

RESULTS

A total of 180 men were included. The mean (SD) age of the sample at death was 67.9 (12.7) years. Of 180, 120 [66.7%]) were found to have had dementia prior to death. Moderate to severe white matter rarefaction (84 of 180 [46.6%]) and arteriolosclerosis (85 of 180 [47.2%]) were common; infarcts, microinfarcts, and microbleeds were not. A simultaneous equations regression model controlling for age and race showed that more years of play was associated with more severe white matter rarefaction (β, 0.16 [95% CI, 0.02-0.29]; P = .03) and greater phosphorylated tau accumulation (DLFC NFTs: β, 0.15 [95% CI, 0.004-0.30]; P = .04; CTE stage: β, 0.27 [95% CI, 0.14-0.41]; P < .001). White matter rarefaction (β, 0.16 [95% CI, 0.02-0.29]; P = .03) and DLFC NFTs (β, 0.16 [95% CI, 0.03-0.28]; P = .01) were associated with dementia. Arteriolosclerosis and years of play were not associated, but arteriolosclerosis was independently associated with dementia (β, 0.21 [95% CI, 0.07-0.35]; P = .003).

CONCLUSIONS AND RELEVANCE

Among older men who had played football and had CTE, more years of football play were associated with more severe white matter rarefaction and greater DLFC NFT burden. White matter rarefaction, arteriolosclerosis, and DLFC NFTs were independently associated with dementia. Dementia in CTE is likely a result of neuropathologic changes, including white matter rarefaction and phosphorylated tau, associated with repetitive head impact and pathologic changes not associated with head trauma, such as arteriolosclerosis.

Nailfold Capillary Morphology in Alzheimer's Disease Dementia

BACKGROUND

Cerebrovascular disease (CVD) is highly comorbid with Alzheimer's disease (AD), yet its role is not entirely understood. Nailfold video capillaroscopy (NVC) is a noninvasive method of live imaging the capillaries near the fingernail's cuticle and may help to describe further vascular contributions to AD.

OBJECTIVE

To examine finger nailfold capillary morphology using NVC in subjects with AD dementia, mild cognitive impairment (MCI), and normal cognition (NC).

METHODS

We evaluated nailfold capillary hemorrhages, avascular zones ≥100 microns, and degree of tortuosity in 28 NC, 15 MCI, and 18 AD dementia subjects using NVC. Tortuosity was measured with a semi-quantitative rating scale. To assess the relation between nailfold capillary morphological features and diagnostic grouping, univariate and multivariable logistic regression models were fit to the data.

RESULTS

56% of subjects with AD dementia compared to 14% with NC and 13% with MCI displayed moderate to severe tortuosity. Greater severity of tortuosity was associated with 10.6-fold (95% confidence interval [CI]: 2.4, 46.2; p = 0.0018) and 7.4-fold (95% CI: 1.3, 41.3; p = 0.023) increased odds of AD dementia relative to NC and MCI, respectively, after adjusting for multiple covariates.

CONCLUSION

Greater nailfold capillary tortuosity was found in participants with AD dementia compared to those with MCI or NC. These data provide preliminary evidence of a systemic microvasculopathy in AD that may be noninvasively and inexpensively evaluated through NVC.

Contact sport participation and chronic traumatic encephalopathy are associated with altered severity and distribution of cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) consists of beta-amyloid deposition in the walls of the cerebrovasculature and is commonly associated with Alzheimer's disease (AD). However, the association of CAA with repetitive head impacts (RHI) and with chronic traumatic encephalopathy (CTE) is unknown. We evaluated the relationship between RHI from contact sport participation, CTE, and CAA within a group of deceased contact sport athletes (n = 357), a community-based cohort (n = 209), and an AD cohort from Boston University AD Center (n = 241). Unsupervised hierarchal cluster analysis demonstrated a unique cluster (n = 11) with increased CAA in the leptomeningeal vessels compared to the intracortical vessels (p < 0.001) comprised of participants with significantly greater frequencies of CTE (7/11) and history of RHI. Overall, participants with CTE (n = 251) had more prevalent (p < 0.001) and severe (p = 0.010) CAA within the frontal leptomeningeal vessels compared to intracortical vessels. Compared to those with AD, participants with CTE had more severe CAA in frontal than parietal lobes (p < 0.001) and more severe CAA in leptomeningeal than intracortical vessels (p = 0.002). The overall frequency of CAA in participants with CTE was low, and there was no significant association between contact sport participation and the presence of CAA. However, in those with CAA, a history of contact sports was associated with increased CAA severity in the frontal leptomeningeal vessels (OR = 4.01, 95% CI 2.52-6.38, p < 0.001) adjusting for AD, APOE ε4 status, and age. Participants with CAA had increased levels of sulcal tau pathology and decreased levels of the synaptic marker PSD-95 (p's < 0.05), and CAA was a predictor of dementia (OR = 1.75, 95% CI 1.02-2.99, p = 0.043) adjusting for age, sex, and comorbid pathology. Overall, contact sport participation and CTE were associated with more severe frontal and leptomeningeal CAA, and CAA was independently associated with worse pathological and clinical outcomes.

Age of first exposure to tackle football and chronic traumatic encephalopathy

OBJECTIVE

To examine the effect of age of first exposure to tackle football on chronic traumatic encephalopathy (CTE) pathological severity and age of neurobehavioral symptom onset in tackle football players with neuropathologically confirmed CTE.

METHODS

The sample included 246 tackle football players who donated their brains for neuropathological examination. Two hundred eleven were diagnosed with CTE (126 of 211 were without comorbid neurodegenerative diseases), and 35 were without CTE. Informant interviews ascertained age of first exposure and age of cognitive and behavioral/mood symptom onset.

RESULTS

Analyses accounted for decade and duration of play. Age of exposure was not associated with CTE pathological severity, or Alzheimer's disease or Lewy body pathology. In the 211 participants with CTE, every 1 year younger participants began to play tackle football predicted earlier reported cognitive symptom onset by 2.44 years (p < 0.0001) and behavioral/mood symptoms by 2.50 years (p < 0.0001). Age of exposure before 12 predicted earlier cognitive (p < 0.0001) and behavioral/mood (p < 0.0001) symptom onset by 13.39 and 13.28 years, respectively. In participants with dementia, younger age of exposure corresponded to earlier functional impairment onset. Similar effects were observed in the 126 CTE-only participants. Effect sizes were comparable in participants without CTE.

INTERPRETATION

In this sample of deceased tackle football players, younger age of exposure to tackle football was not associated with CTE pathological severity, but predicted earlier neurobehavioral symptom onset. Youth exposure to tackle football may reduce resiliency to late-life neuropathology. These findings may not generalize to the broader tackle football population, and informant-report may have affected the accuracy of the estimated effects. Ann Neurol 2018;83:886-901.

Independent effects of white matter hyperintensities on cognitive, neuropsychiatric, and functional decline: a longitudinal investigation using the National Alzheimer's Coordinating Center Uniform Data Set

BACKGROUND

Longitudinal investigations are needed to improve understanding of the contributions of cerebral small vessel disease to the clinical manifestation of Alzheimer's disease, particularly in the early disease stages. This study leveraged the National Alzheimer's Coordinating Center Uniform Data Set to longitudinally examine the association between white matter hyperintensities and neuropsychological, neuropsychiatric, and functional decline among participants with normal cognition.

METHODS

The sample included 465 participants from the National Alzheimer's Coordinating Center Uniform Data Set who had quantitated volume of white matter hyperintensities from fluid-attenuated inversion recovery MRI, had normal cognition at the time of their MRI, and were administered the National Alzheimer's Coordinating Center Uniform Data Set neuropsychological test battery within 1 year of study evaluation and had at least two post-MRI time points of clinical data. Neuropsychiatric status was assessed by the Geriatric Depression Scale-15 and Neuropsychiatric Inventory-Questionnaire. Clinical Dementia Rating Sum of Boxes defined functional status. For participants subsequently diagnosed with mild cognitive impairment (MCI) or dementia, their impairment must have been attributed to Alzheimer's disease (AD) to evaluate the relationships between WMH and the clinical presentation of AD.

RESULTS

Of the 465 participants, 56 converted to MCI or AD dementia (average follow-up = 5 years). Among the 465 participants, generalized estimating equations controlling for age, sex, race, education, APOE ε4, and total brain and hippocampal volume showed that higher baseline log-white matter hyperintensities predicted accelerated decline on the following neuropsychological tests in rank order of effect size: Trails B (p < 0.01), Digit Symbol Coding (p < 0.01), Logical Memory Immediate Recall (p = 0.02), Trail Making A (p < 0.01), and Semantic Fluency (p < 0.01). White matter hyperintensities predicted increases in Clinical Dementia Rating Sum of Boxes (p < 0.01) and Geriatric Depression Scale-15 scores (p = 0.01). Effect sizes were comparable to total brain and hippocampal volume. White matter hyperintensities did not predict diagnostic conversion. All effects also remained after including individuals with non-AD suspected etiologies for those who converted to MCI or dementia.

CONCLUSIONS

In this baseline cognitively normal sample, greater white matter hyperintensities were associated with accelerated cognitive, neuropsychiatric, and functional decline independent of traditional risk factors and MRI biomarkers for Alzheimer's disease.

Youth Exposure to Repetitive Head Impacts From Tackle Football and Long-term Neurologic Outcomes: A Review of the Literature, Knowledge Gaps and Future Directions, and Societal and Clinical Implications

Youth participation in contact and collision sports, particularly tackle football, is associated with exposure to repetitive head impacts during a time period when tremendous brain maturation is occurring. Accumulating evidence suggests that exposure to repetitive head impacts from youth tackle football may increase vulnerability to long-term cognitive, neuropsychiatric, and neurologic disturbances. There are limitations to the current literature and conflicting findings exist. Nonetheless, participation in youth football has become a cause of concern to clinicians, scientists, politicians, coaches, parents, and children. The objective of this paper is to review the literature on the long-term cognitive, neuropsychiatric, and neurologic outcomes associated with participation in youth contact and collision sports, with a focus on tackle football. We provide an overview of the empirically derived framework that has served as the foundation for the investigation of youth tackle football and neurologic outcomes. The extant research studies on age of first exposure to tackle football and later-life cognitive and neuropsychiatric functioning, as well as structural brain changes are reviewed. We discuss the limitations of the current evidence, suggest future directions, and conclude with our opinions on societal and clinical implications.

A Clinicopathological Investigation of White Matter Hyperintensities and Alzheimer's Disease Neuropathology

BACKGROUND

White matter hyperintensities (WMH) on magnetic resonance imaging (MRI) have been postulated to be a core feature of Alzheimer's disease. Clinicopathological studies are needed to elucidate and confirm this possibility.

OBJECTIVE

This study examined: 1) the association between antemortem WMH and autopsy-confirmed Alzheimer's disease neuropathology (ADNP), 2) the relationship between WMH and dementia in participants with ADNP, and 3) the relationships among cerebrovascular disease, WMH, and ADNP.

METHODS

The sample included 82 participants from the National Alzheimer's Coordinating Center's Data Sets who had quantitated volume of WMH from antemortem FLAIR MRI and available neuropathological data. The Clinical Dementia Rating (CDR) scale (from MRI visit) operationalized dementia status. ADNP+ was defined by moderate to frequent neuritic plaques and Braak stage III-VI at autopsy. Cerebrovascular disease neuropathology included infarcts or lacunes, microinfarcts, arteriolosclerosis, atherosclerosis, and cerebral amyloid angiopathy.

RESULTS

60/82 participants were ADNP+. Greater volume of WMH predicted increased odds for ADNP (p = 0.037). In ADNP+ participants, greater WMH corresponded with increased odds for dementia (CDR≥1; p = 0.038). WMH predicted cerebral amyloid angiopathy, microinfarcts, infarcts, and lacunes (ps < 0.04). ADNP+ participants were more likely to have moderate-severe arteriolosclerosis and cerebral amyloid angiopathy compared to ADNP-participants (ps < 0.04).

CONCLUSIONS

This study found a direct association between total volume of WMH and increased odds for having ADNP. In patients with Alzheimer's disease, FLAIR MRI WMH may be able to provide key insight into disease severity and progression. The association between WMH and ADNP may be explained by underlying cerebrovascular disease.

Limbic system structure volumes and associated neurocognitive functioning in former NFL players

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts. CTE has been linked to disruptions in cognition, mood, and behavior. Unfortunately, the diagnosis of CTE can only be made post-mortem. Neuropathological evidence suggests limbic structures may provide an opportunity to characterize CTE in the living. Using 3 T magnetic resonance imaging, we compared select limbic brain regional volumes - the amygdala, hippocampus, and cingulate gyrus - between symptomatic former National Football League (NFL) players (n = 86) and controls (n = 22). Moreover, within the group of former NFL players, we examined the relationship between those limbic structures and neurobehavioral functioning (n = 75). The former NFL group comprised eighty-six men (mean age = 55.2 ± 8.0 years) with at least 12 years of organized football experience, at least 2 years of active participation in the NFL, and self-reported declines in cognition, mood, and behavior within the last 6 months. The control group consisted of men (mean age = 57.0 ± 6.6 years) with no history of contact-sport involvement or traumatic brain injury. All control participants provided neurobehavioral data. Compared to controls, former NFL players exhibited reduced volumes of the amygdala, hippocampus, and cingulate gyrus. Within the NFL group, reduced bilateral cingulate gyrus volume was associated with worse attention and psychomotor speed (r = 0.4 (right), r = 0.42 (left); both p < 0.001), while decreased right hippocampal volume was associated with worse visual memory (r = 0.25, p = 0.027). Reduced volumes of limbic system structures in former NFL players are associated with neurocognitive features of CTE. Volume reductions in the amygdala, hippocampus, and cingulate gyrus may be potential biomarkers of neurodegeneration in those at risk for CTE.

Neuropsychiatric Symptoms and the Diagnostic Stability of Mild Cognitive Impairment

BACKGROUND

Mild cognitive impairment (MCI) is an intermediate diagnosis between normal cognition (NC) and dementia, including Alzheimer's disease (AD) dementia. However, MCI is heterogeneous; many individuals subsequently revert to NC while others remain stable at MCI for several years. Identifying factors associated with this diagnostic instability could assist in defining clinical populations and determining cognitive prognoses.

OBJECTIVE

The current study examined whether neuropsychiatric symptoms could partially account for the temporal instability in cognitive diagnoses.

METHOD

The sample included 6,763 participants from the National Alzheimer's Coordinating Center Uniform Data Set. All participants had NC at baseline, completed at least two follow-up visits (mean duration: 5.5 years), and had no recent neurological conditions. Generalized linear models estimated by generalized estimating equations examined associations between changes in cognitive diagnoses and symptoms on the Neuropsychiatric Inventory Questionnaire (NPI-Q) and Geriatric Depression Scale (GDS-15).

RESULTS

1,121 participants converted from NC to MCI; 324 reverted back to NC and 242 progressed to AD dementia. Higher symptoms on the GDS-15 and circumscribed symptom domains on the NPI-Q were associated with conversion from NC to MCI and a decreased likelihood of reversion from MCI to NC. Individuals with higher symptoms on NPI-Q Hyperactivity and Mood items were more likely to progress to AD dementia.

DISCUSSION

The temporal instability of MCI can be partially explained by neuropsychiatric symptoms. Individuals with higher levels of specific symptoms are more likely to progress to AD dementia and less likely to revert to NC. Identification and treatment of these symptoms might support cognitive functioning in older adults.