Clinical value of CSF amyloid-beta-42 and tau proteins in Progressive Supranuclear Palsy

Progressive Supranuclear Palsy (PSP) is a four-repeat tauopathy with high phenotypic and neuropathological variability, highlighting the urgent need for effective disease biomarkers. Quantitative analysis of cerebrospinal fluid (CSF) proteins reflecting pathological changes of CNS is currently used as biomarkers of multiple neurodegenerative disorders for both early differential diagnosis and prognostic clustering of patients. In this study, we thus assessed the clinical usefulness of a panel of CSF biomarker in PSP patients presenting with Richardson's Syndrome. CSF levels of 42-beta-amyloid, total-tau, phosphorylated-tau, and both 42-beta-amyloid/phosphorylated-tau and phosphorylated-tau/total-tau ratios were comparatively evaluated in 39 PSP patients, 31 patients with Parkinson's Disease (PD) and 58 gender-/age-matched healthy controls. Specific gold-standard clinical scores were obtained. Diagnostic accuracy and clinical correlates of each biomarker were measured with receiver operating curve analysis and Spearman's test/linear regression, respectively. In PSP, 42-beta-amyloid was lower than either controls or PD; total-tau and phosphorylated-tau were instead reduced compared to controls, but similar to PD. At the cut-off value of 623 pg/ml, 42-beta-amyloid significantly distinguished PSP from controls and PD. Likewise, phosphorylated-tau/total-tau ratio also supported differential diagnosis between PSP and PD (cut-off = 0.185). 42-beta-amyloid was inversely associated with PSP severity, as measured with PSP Rating Scale. Our study demonstrates that CSF 42-beta-amyloid is reduced in PSP patients, proportionally to clinical severity, thus suggesting a potential use as disease biomarker. Moreover, phosphorylated-tau/total-tau ratio resulted helpful in the early differential diagnosis between PSP and PD.