Plasma pTau217 as a Prognostic, Monitoring, and Risk-Stratification Biomarker of Clinical Progression in Lewy Body Disease

Background and Objectives: In Lewy body disease (LBD), co-occurring Alzheimer's disease (AD) neuropathologic change (ADNC) is associated with worse clinical outcomes. While plasma pTau217 detects ADNC in LBD, its prognostic, monitoring, and risk-stratification utility remains unclear. We evaluated whether plasma pTau217 predicted cognitive and functional decline and risk for progression to MCI or dementia in LBD. Methods: We included 501 participants enrolled in the Stanford Alzheimer's Disease Research Center with plasma pTau217 data who were clinically diagnosed as LBD spectrum (n = 131), AD spectrum (n = 133), or healthy controls (HC; n = 237). To assess prognostic and monitoring utility in LBD, linear mixed-effect models tested continuous baseline and longitudinal (2-5 years) plasma pTau217 as predictors of change in 2-8-year clinical outcome trajectories including: daily functioning (CDR-SB), global cognition (MoCA), and five domain-specific cognitive indices. For risk-stratification in LBD, baseline plasma pTau217 was dichotomized using an amyloid PET-derived, LBD-specific cut-point to examine effects of abnormal versus normal levels on clinical outcomes in separate mixed-effects and survival models. Results: In LBD, higher continuous baseline plasma pTau217 predicted accelerated CDR-SB increase ({beta} = 0.29, p < 0.001), MoCA decline ({beta} = -0.37, p = 0.014), and cognitive index decline (memory, executive function, visuospatial function, processing speed; {beta}s = -2.24 to -0.06, ps [&le;] 0.01). Faster longitudinal pTau217 increase predicted accelerated CDR-SB increase ({beta} = 0.24, p = 0.001). In AD, higher continuous baseline pTau217 predicted accelerated CDR-SB increase and MoCA decline, whereas faster longitudinal increase predicted accelerated cognitive index decline (ps [&le;] 0.04). In HC, higher continuous baseline pTau217 predicted accelerated memory index decline (p = 0.008). In LBD, abnormal baseline pTau217 predicted a 0.87 points/year (95% CI: -1.62, -0.58) faster MoCA decline, 0.85 points/year (95% CI: 0.56, 1.14) faster CDR-SB increase, accelerated decline on cognitive indices, and a three-fold higher risk of progressing to MCI or dementia (HR = 3.41, 95% CI 1.60, 7.28, p = 0.002) compared to normal pTau217. Discussion: Plasma pTau217 is a promising prognostic, monitoring, and risk stratification biomarker of clinical progression in LBD, underscoring its utility in mixed pathology groups for clinical practice and trials.