Fluid Biomarkers of Disease Burden and Cognitive Dysfunction in Progressive Supranuclear Palsy

Identifying objective biomarkers for progressive supranuclear palsy (PSP) is crucial to improving diagnosis and establishing clinical trial and treatment endpoints. This study evaluated fluid biomarkers in PSP versus controls and their associations with regional ¹⁸F-PI-2620 tau-PET, clinical, and cognitive outcomes.

Twenty-four PSP patients and 11 age- and sex-matched control subjects underwent Cerebrospinal fluid (CSF) and plasma assays of neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), and total tau (t-tau) using SIMOA. Ratios (NfL/t-tau, GFAP/t-tau, GFAP/NfL) were calculated. Tau burden was quantified using PI-2620 distribution volume ratio (DVR). Group comparisons and associations with tau-PET, MRI, and cognition were tested using Wilcoxon tests, ROC analyses, and age- and sex-adjusted linear models.

PSP patients showed elevated NfL, GFAP levels, and higher NfL/t-tau and GFAP/t-tau ratios in CSF and plasma. CSF NfL/t-tau best discriminated PSP from control subjects (AUC = 0.99, 95% CI [0.97-1.00]; optimal cut-off: > 10), followed by CSF GFAP/t-tau (AUC = 0.89, 95% CI [0.76-1.00]; > 104) and plasma NfL/t-tau (AUC = 0.80, 95% CI [0.63-0.96]; 5.1). Plasma NfL/t-tau correlated with tau-PET DVR in the putamen (β = 0.63; 95% CI [0.15-1.11]; p < 0.01) and pallidum (β = 0.54, 95% CI [0.07-1.02]; p < 0.01) and predicted disease severity (β = 0.61, 95% CI [0.19, 1.04]; p = 0.007) and processing speed (β = 0.66, 95% CI [0.22, 1.10]; p = 0.006), explaining 35% and 33% of variance, respectively. Frontal MRI volume modestly improved prediction of processing speed (ΔR²adj = 0.23, p = 0.01), whereas tau-PET did not.

Plasma NfL/t-tau correlates with regional tau, disease severity, and cognition. Fluid biomarkers, complemented by PET and MRI, may support multimodal PSP diagnosis, monitoring, and trial stratification.

Australian New Zealand Clinical Trials Registry: ACTRN12620001254987.