Educational and Clinical Associations With Longitudinal Cognitive Function and Brain Imaging in American Indians

Abstract

BACKGROUNDLittle is known about incidence of vascular and Alzheimer’s dementias in American Indians. METHODS We conducted a large, heterogeneous, population-based, longitudinal cohort study of brain aging in community-dwelling American Indians aged 64-95 years from 11 tribes across 3 states, with neurological examinations, 1.5T magnetic resonance imaging (MRI), and extensive cognitive testing. Visit 1 in 2010-2013 (n=817) and Visit 2 in 2017-2019 (n=403) included all willing, surviving participants. Standardized cognitive tests at both visits included Modified Mini Mental Status Examination (3MSE), Wechsler Adult Intelligence Scale digit symbol coding (WAIS), Controlled Oral Word Association fas (COWA), California Verbal Learning Test short form (CVLT). Test materials added at follow-up included Wide Range Achievement (reading) Test (WRAT) and National Alzheimer’s Coordinating Center Uniform Data Set cognitive battery (v3 form C2) , including Montreal Cognitive Assessment (MoCA). MRI neuroradiologists coded infarcts, hemorrhages, white matter hyperintensities, sulcal atrophy, and ventricle enlargement. RESULTS Mean time between exams was 6.7 years (SD 1.1, range 3.8-9.1). Years of formal education had modest correlation with WRAT reading score (r=0.45). Prevalence and incidence of infarcts were (respectively) 32% and 12.8/1000 person-years (PY); hemmorhages 6% and 4.4/1000 PY; worsening sulci 74% and 19.0/1000 PY; wosening ventricle 79% and 30.1/1000 PY; worsening leukoaraiosis 44% and 26.1/1000 PY. Linear losses per year in cognitive scores were 0.6% 3MSE, 1.2% WAIS, 0.6% COWA, 2.2% CVLT. Mean MoCA scores were 18.9 (SD 4.3). DISCUSSION These are the first data on longitudinal cognitive and imaging changes in American Indians, as well as first reports of AD related features. Mean scores in MoCA were similar or lower than standard cutoffs used to diagnose dementia in other racial/ethnic groups, suggesting that standardized cognitive tests may not perform well in this population. Test validation, adaptation, and score adjustment are warranted. Years of education was a poor proxy for premorbid function, suggesting novel methods for cognitive score contextualization is also needed in this population. Evaluation of selective survival suggests attrition from death and frailty should be accounted for in causal analyses. Overall, these data represent a unique opportunity to examine neurology topics of critical importance to an understudied population.

Improving Our Understanding of Cognitive Aging in American Indian Peoples

“…Declines in performance over time in the study of Suchy-Dicey et al 3 were noted in all serially tested cognitive measures. While this is not an unexpected finding in an aging cohort, these data are valuable for several reasons.…”

“…Generating regionally and culturally specific neuropsychological data sets is critically important because psychometric assessments must be contextually framed to yield interpretable, clinically meaningful results. 4 The study results of Sucy-Dicey et al 3 further highlight the need to place psychometric data in appropriate social and cultural contexts. For instance, the average score of their cohort on the MoCA, a widely used screening instrument for dementia, was 18.9 (SD 4.3), which is at or lower than the standard cutoff used to diagnose dementia in other populations.…”

“…In particular, American Indian peoples are at higher risk of developing Alzheimer disease and related disorders compared with non-Hispanic White persons, with approximately 35% of American Indian elders developing dementia between the ages of 65 and 90 years, compared with 30% of non-Hispanic White elders. 1,2 In this issue of Neurology ® , Suchy-Dicey et al 3 examine longitudinal changes in cognitive performance and brain structures in a large cohort of older American Indian peoples, adding valuably to our understanding of the emergence of cognitive changes in this population.…”

“…This aligns with other evidence suggesting that years of education may not be as informative a measure in minoritized populations as in White populations, unless one also accounts for differences in the quality of education that exist because of systematic educational segregation 5,6 . In short, Suchy-Dicey et al 3 provide evidence that the field may require greater flexibility, cultural sensitivity, and population-specificity to adequately characterize cognition across the diverse range of individual experiences.…”

“…Suchy-Dicey et al 3 conducted a longitudinal cohort study of brain aging in community-dwelling American Indian peoples aged 64–95 years from 11 tribes across 3 states. Participants received initial neurologic examinations, cognitive assessments, and brain MRI scans between the years 2010–2013 (n = 817) and similar follow-up evaluations between the years 2017–2019 (n = 403).…”