PET staging of amyloidosis using striatum.

INTRODUCTION: Amyloid positron emission tomography (PET) data are commonly expressed as binary measures of cortical deposition. However, not all individuals with high cortical amyloid will experience rapid cognitive decline. Motivated by postmortem data, we evaluated a three-stage PET classification: low cortical; high cortical, low striatal; and high cortical, high striatal amyloid; hypothesizing this model could better reflect Alzheimer's dementia progression than a model based only on cortical measures. METHODS: We classified PET data from 1433 participants (646 normal, 574 mild cognitive impairment, and 213 AD), explored the successive involvement of cortex and striatum using 3-year follow-up PET data, and evaluated the associations between PET stages, hippocampal volumes, and cognition. RESULTS: Follow-up data indicated that PET detects amyloid first in cortex and then in striatum. Our three-category staging including striatum better predicted hippocampal volumes and subsequent cognition than a three-category staging including only cortical amyloid. DISCUSSION: PET can evaluate amyloid expansion from cortex to subcortex. Using striatal signal as a marker of advanced amyloidosis may increase predictive power in Alzheimer's dementia research.

Association of Higher Cortical Amyloid Burden With Loneliness in Cognitively Normal Older Adults.

IMPORTANCE: Emotional and behavioral symptoms in cognitively normal older people may be direct manifestations of Alzheimer disease (AD) pathophysiology at the preclinical stage, prior to the onset of mild cognitive impairment. Loneliness is a perceived state of social and emotional isolation that has been associated with cognitive and functional decline and an increased risk of incident AD dementia. We hypothesized that loneliness might occur in association with elevated cortical amyloid burden, an in vivo research biomarker of AD. OBJECTIVE: To determine whether cortical amyloid burden is associated with greater loneliness in cognitively normal older adults. DESIGN, SETTING, AND PARTICIPANTS: Cross-sectional analyses using data from the Harvard Aging Brain Study of 79 cognitively normal, community-dwelling participants. A continuous, aggregate measure of cortical amyloid burden, determined by Pittsburgh Compound B-positron emission tomography (PiB-PET), was examined in association with loneliness in linear regression models adjusting for age, sex, apolipoprotein E ε4 (APOEε4), socioeconomic status, depression, anxiety, and social network (without and with the interaction of amyloid and APOEε4). We also quantified the association of high amyloid burden (amyloid-positive group) to loneliness (lonely group) using logistic regression, controlling for the same covariates, with the amyloid-positive group and the lonely group, each composing 32% of the sample (n = 25). MAIN OUTCOMES AND MEASURES: Loneliness, as determined by the 3-item UCLA Loneliness Scale (possible range, 3-12, with higher score indicating greater loneliness). RESULTS: The 79 participants included 43 women and 36 men with a mean (SD) age of 76.4 (6.2) years. Mean (SD) cortical amyloid burden via PiB-PET was 1.230 (0.209), and the mean (SD) UCLA-3 loneliness score was 5.3 (1.8). Twenty-two (28%) had positive APOEε4 carrier status, and 25 (32%) were in the amyloid-positive group with cortical PiB distribution volume ratio greater than 1.2. Controlling for age, sex, APOEε4, socioeconomic status, depression, anxiety, and social network, we found that higher amyloid burden was significantly associated with greater loneliness: compared with individuals in the amyloid-negative group, those in the amyloid-positive group were 7.5-fold (95% CI, 1.7-fold to 34.0-fold) more likely to be classified as lonely than nonlonely (ß = 3.3, partial r = 0.4, P = .002). Furthermore, the association of high amyloid burden and loneliness was stronger in APOEε4 carriers than in noncarriers. CONCLUSIONS AND RELEVANCE: We report a novel association of loneliness with cortical amyloid burden in cognitively normal older adults, suggesting that loneliness is a neuropsychiatric symptom relevant to preclinical AD. This work will inform new research into the neural underpinnings and disease mechanisms involved in loneliness and may enhance early detection and intervention research in AD.

Subjective cognitive concerns, amyloid-ß, and neurodegeneration in clinically normal elderly.

OBJECTIVE: To determine whether neuroimaging biomarkers of amyloid-ß (Aß) and neurodegeneration (ND) are associated with greater self-reported subjective cognitive concerns (SCC) in clinically normal older individuals. METHODS: A total of 257 participants underwent Pittsburgh compound B PET, PET with fluorodeoxyglucose (18)F, and structural MRI, as well as a battery of neuropsychological measures including several questionnaires regarding SCC. Individuals were classified into 4 biomarker groups: biomarker negative (Aß-/ND-), amyloidosis alone (Aß+/ND-), amyloidosis plus ND (Aß+/ND+), and ND alone (Aß-/ND+). RESULTS: Both Aß and ND were independently associated with greater SCC controlling for objective memory performance. By contrast, neither Aß nor ND was associated with objective memory performance controlling for SCC. Further examination revealed greater SCC in individuals with Aß or ND positivity compared to biomarker-negative individuals. In addition, greater SCC predicted Aß positivity when controlling for ND status. CONCLUSIONS: When individuals were grouped by biomarker status, those who were positive on Aß or ND had the highest report of SCC compared to biomarker-negative individuals. Findings were consistent when SCC was used to predict Aß positivity. Taken together, results suggest that both Aß and ND are associated with SCC, independent of objective memory performance. Enrichment of individuals with SCC may increase likelihood of Aß and ND markers in potential participants for secondary prevention trials.

Free and cued memory in relation to biomarker-defined abnormalities in clinically normal older adults and those at risk for Alzheimer's disease.

OBJECTIVES: Furthering our understanding of the relationship between amyloidosis (Aß), neurodegeneration (ND), and cognition is imperative for early identification and early intervention of Alzheimer's disease (AD). However, the subtle cognitive decline differentially associated with each biomarker-defined stage of preclinical AD has yet to be fully characterized. Recent work indicates that different components of memory performance (free and cued recall) may be differentially specific to memory decline in prodromal AD. We sought to examine the relationship between free and cued recall paradigms, in addition to global composites of memory, executive functioning, and processing speed in relation to stages of preclinical AD. METHODS: A total of 260 clinically normal (CN) older adults (CDR=0) from the Harvard Aging Brain study were grouped according to preclinical AD stages including Stage 0 (Aß-/ND-), Stage 1 (Aß+/ND-), Stage 2 (Aß+/ND+), and suspected non-Alzheimer's associated pathology (SNAP; Aß-/ND+). General linear models controlling for age, sex, and education were used to assess for stage-based performance differences on cognitive composites of executive functioning, processing speed, and memory in addition to free and cued delayed recall on the Selective Reminding Test (SRT) and Memory Capacity Test (MCT). RESULTS: Global memory performance differed between preclinical stages with Stage 2 performing worse compared with Stage 0. When examining free and cued paradigms by memory test, only the MCT (and not the SRT) revealed group differences. More specifically, Stage 1 was associated with decrements in free recall compared with Stage 0 while Stage 2 was associated with decrements in both free and cued recall. There was a trend for the SNAP group to perform worse on free recall compared with Stage 0. Finally, there was no association between preclinical stage and global composites of executive functioning or processing speed. CONCLUSIONS: Clinically normal older adults with underlying evidence of amyloidosis and neurodegeneration exhibit subtle, yet measurable differences in memory performance, but only on a challenging associative test. The sensitivity of free vs. cued memory paradigms may be dependent on preclinical stage such that reduced free recall is associated with amyloidosis alone (Stage 1) while a decline in cued recall may represent progression to amyloidosis and neurodegeneration (Stage 2). These findings may have practical applications for clinical assessment and clinical trial design.

Cognitive profile of amyloid burden and white matter hyperintensities in cognitively normal older adults.

Amyloid burden and white matter hyperintensities (WMH) are two common markers of neurodegeneration present in advanced aging. Each represents a potential early indicator of an age-related neurological disorder that impacts cognition. The presence of amyloid is observed in a substantial subset of cognitively normal older adults, but the literature remains equivocal regarding whether amyloid in nondemented populations is deleterious to cognition. Similarly, WMH are detected in many nondemented older adults and there is a body of evidence indicating that WMH are associated with decreased executive function and other cognitive domains. The current study investigated amyloid burden and WMH in clinically normal older adult humans aged 65-86 (N = 168) and examined each biomarker's relation with cognitive domains of episodic memory, executive function, and speed of processing. Factors for each domain were derived from a neuropsychological battery on a theoretical basis without reference to the relation between cognition and the biomarkers. Amyloid burden and WMH were not correlated with one another. Age was associated with lower performance in all cognitive domains, while higher estimated verbal intelligence was associated with higher performance in all domains. Hypothesis-driven tests revealed that amyloid burden and WMH had distinct cognitive profiles, with amyloid burden having a specific influence on episodic memory and WMH primarily associated with executive function but having broad (but lesser) effects on the other domains. These findings suggest that even before clinical impairment, amyloid burden and WMH likely represent neuropathological cascades with distinct etiologies and dissociable influences on cognition.