Alzheimer's disease (AD) is defined by its characteristic neuropathologic changes, which allow for diagnosis and assessment of severity. Recently, the Alzheimer's Association proposed a framework to stage Alzheimer's disease biologically based on tau-PET. Furthermore, the framework hypothesizes a degree of alignment between biological Alzheimer's disease severity and clinical symptom severity. We aimed to investigate the concordance between clinical and biological stages of Alzheimer's disease and explore factors contributing to discordance using in vivo and postmortem neuropathological data. Data from 768 amyloid-β positive individuals were drawn from four observational cross-sectional in vivo cohorts-TRIAD, ADNI, HABS-HD, and SCAN-as well as a postmortem autopsy dataset from the National Alzheimer's Coordinating Center (NACC; n = 3,188). All in vivo participants had tau-PET imaging, clinical diagnosis, and neurobehavioral assessments. Participants were assigned a biological Alzheimer's disease stage based on their tau-PET scan according to the Alzheimer's Association revised criteria stages. The autopsy dataset included individuals with moderate-to-frequent neuritic plaques (CERAD scores 2-3), along with premortem clinical and neurobehavioral data. Clinical-biological concordance was quantified using squared-weighted Cohen's Kappa. Ordinal and linear regression models assessed associations between biological stage and clinical severity (CDR-Sum of Boxes, MMSE), adjusting for age, sex, and cohort. Postmortem analyses evaluated the impact of comorbid neuropathologies on clinical-biological discordance using adjusted odds ratios and ordinal regression. Overall concordance between clinical and biological Alzheimer's disease staging was moderate (Cohen's Kappa=0.52, p < 0.001). Approximately 70% of individuals classified as cognitively unimpaired or with dementia exhibited biological stages consistent with their clinical diagnoses. In contrast, transitional decline and mild cognitive impairment (MCI) groups were more heterogenous. Notably, 25% of Aβ-positive individuals with MCI demonstrated no detectable tau-PET abnormality. Nonetheless, advanced tau-PET stage was reliably associated with clinical impairment. In the NACC autopsy dataset, nearly all individuals with more severe clinical stage than their proposed biological stage exhibited comorbid neuropathologies, including FTLD-TDP-43, FTLD-tau, Lewy bodies, LATE, and cerebrovascular disease. The number of comorbid pathologies was strongly associated with increased odds of clinical dementia (t = 8.45, p < 0.001). While there is moderate agreement between clinical and biological stages of Alzheimer's disease across the entire disease spectrum, strong agreement is found in clinically unimpaired and dementia stages. Comparison of clinical and biological Alzheimer's disease stages provides a framework for understanding the large contributions of non-AD neurodegenerative diseases to dementia in Aβ-positive individuals. Our results have important implications for clinical trial recruitment strategies and highlight the urgent need for biomarkers for non-AD pathological processes.
Keywords: Alzheimer’s disease; PET imaging; clinicopathological concordance; staging.
© The Author(s) 2026. Published by Oxford University Press on behalf of the Guarantors of Brain.