Longitudinal tau aggregation, atrophy, and cognitive decline in Alzheimer's disease

The independent contributions of baseline and longitudinal tau positron emission tomography (PET) and magnetic resonance imaging (MRI) to cognitive decline remain unclear.

We included n = 761 amyloid-positive individuals from the Swedish BioFINDER-2 study with [¹⁸F]RO948-tau-PET, 3-Tesla structural-MRI, and cognition (n = 322 with longitudinal imaging data). Linear-mixed-models with random-intercepts and -slopes or linear-regressions were adjusted for age, sex, education, diagnosis, and other-imaging-modality.

Tau-PET showed stronger associations with cognitive decline than MRI, showing the strongest associations in a neocortical-composite-region with a cognitive composite (β = -0.25 ± 0.02, p < 0.001) for baseline and longitudinal tau-PET (β = -0.62 ± 0.05, p < 0.001). Baseline tau-PET explained the largest proportion of cognitive decline (54.0%-94.0%), with modest mediation effects for longitudinal tau-PET or MRI pathways (2.0%-15.0%). Simulated reductions of tau-PET-slopes (up to 100%) were associated with marginally altered cognitive trajectories.

The strong associations between baseline tau-PET and longitudinal cognition, with marginal contributions of longitudinal tau-PET and MRI, emphasize the importance of baseline tau aggregates for prognostics and treatments in Alzheimer's disease (AD).

Baseline and longitudinal regional tau-PET uptake were more closely associated than structural MRI with longitudinal cognitive decline. Baseline tau-PET was a stronger determinant of longitudinal cognitive decline than longitudinal tau-PET. Simulated reductions of tau-PET accumulation showed limited alterations of cognitive trajectories, with potential implications for tau-targeting therapies.