Limbic-predominant neuroimaging correlates of plasma p-Tau217 in preclinical and clinical Alzheimer’s disease

Background: Plasma phosphorylated tau at threonine 217 (p-Tau217) has emerged as a highly sensitive and specific blood-based biomarker for Alzheimer's Disease (AD). However, its regional brain correlates with multimodal neuroimaging, beyond tau-PET, remain underexplored, particularly in early disease phases where limbic involvement may predominate. This study aimed to map the associations of plasma p-Tau217 with amyloid-PET burden, FDG-PET metabolism, and structural brain morphometry in a well-characterized cohort spanning cognitively unimpaired (CU) and cognitively impaired (CI) individuals across AD dementia stages, hypothesizing increased AD neuroimaging biomarkers in individuals with elevated p-Tau217. Methods: We analyzed data from 259 participants from the University of Kansas Alzheimer's Disease Research Center (KU ADRC) Clinical Cohort. Imaging outcomes included amyloid-PET, FDG-PET, gray matter volumetric regions of interest as well as whole brain voxel-based morphometry (VBM), and surface-based morphometry (SBM) for cortical thickness (CT), sulcal depth (SD), gyrification index (GI), fractal dimension (FD). Analyses were stratified by diagnostic and pTau-217 positivity (CU pTau + , CU pTau -, CI pTau + and CI pTau-). Spearman's correlations and voxel/surface-wise regressions evaluated p-Tau217 associations with imaging metrics, accounting for age and sex. Results: Plasma p-Tau217 was elevated in CI versus CU. Individuals with elevated plasma p-Tau217 had increased amyloid-PET deposition across the cortex, as well as significantly higher centiloids, both in CU and CI individuals. In CI individuals, elevated p-Tau217 was associated with reduced voxel-wise gray matter volume and cortical thickness in limbic, temporal, parietal, and frontal regions, plus increased cingulate FD. In both CU and CI pTau + individuals, p-Tau217 correlated with AD Signature gray matter decreases. Conclusion: These findings show that CU and CI individuals with elevated plasma p-Tau217 have both increased amyloid-PET burden but also temporolimbic gray matter atrophy and hypometabolism. This supports p-Tau217 as a minimally invasive, scalable biomarker for early AD detection, risk stratification, and prognostic monitoring in preclinical stages, potentially guiding trial enrichment and personalized interventions.