Tau Tangles in Parkinson's Disease: A 2-Year Follow-Up Flortaucipir PET Study

Background: Flortaucipir PET, a marker of tau tangles, has shown lower than expected cortical uptake in Parkinson's disease (PD), than would be predicted from neuropathologic estimates of Alzheimer's disease co-pathology. Instead, the most characteristic finding of flortaucipir imaging in PD is decreased uptake in the substantia nigra, reflecting reduction in its 'off-target' binding to neuromelanin. We have previously reported these observations in cross-sectional studies. Objective: Here, we present two-year follow-up data of cortical and nigral flortaucipir uptake in PD patients. Methods: Seventeen PD patients received repeat flortaucipir PET two years after baseline. We interrogated vertex-based group-wise cortical tracer binding (SUVRs) with a cerebellar reference using the general linear model while mean substantia nigra SUVRs were compared with volumes of interest group comparisons and voxel-wise group analyses using ANOVA. Finally, we performed linear regressions of tau load with changes in MoCA and UPDRS motor scores. Results: We found no significant changes in substantia nigra or cortex flortaucipir uptake in Parkinson's disease patients over two years and no association with changes in cognitive symptoms. Signal reduction in the medial substantia nigra trended towards an association with worsening of motor symptoms. Conclusion: No significant increase in tau tangles occurred after a two-year follow-up of Parkinson's disease patients using flortaucipir PET.