Tau in Atypical Parkinsonisms: A Meta-Analysis of in Vivo PET Imaging Findings

Background Progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are atypical parkinsonisms (APs) that are classified as tauopathies. Patients with these APs may present with similar early clinical manifestations to Parkinson's disease (PD), but they prove unresponsive to anti-parkinsonian medications.Objective The main objective of this meta-analysis was to compare first- and second-generation tau PET tracer efficacy in patients with the APs to identify potential diagnostic biomarkers.MethodsPubMed and Web of Science were searched between January 1, 1999 and December 31, 2022. We included case-control studies that were published in English and report tau PET tracer binding as mean +/- SD in at least one region of interest (ROI). Differences in tau PET binding values were meta-analyzed using random-effects meta-analytic models and subgroup analyses based on ROIs in the statistical programming language R (version 4.2.1).Results Overall, 29 studies with 665 patients were included in the final review. [F-18]PI-2620 outperformed first-generation tracers when comparing PSP-HC (g = -1.68, 95% CI: -2.05 to -1.30) and CBD-HC (g = -1.37, 95% CI: -2.25 to -0.49). When comparing PSP-PD, the first-generation tracer, [F-18]AV-1451, presented with higher binding to PSP patients (g = -0.80, 95% CI: -1.24 to -0.35).Conclusions Our results demonstrate the efficacy of [F-18]PI-2620 PET in imaging AP-tau. These findings contribute towards identifying a diagnostic imaging biomarker for patients with APs. The main limitation of this study was the heterogeneity of the results. Future studies should conduct AP-PD comparisons with second-generation tracers to confirm the preliminary results found here.