Validation of the new pathology staging system for progressive supranuclear palsy
Progressive supranuclear palsy (PSP) is a neurodegenerative disorder associated with neuroglial accumulation of 4-repeat tau protein. Kovacs et al. have recently proposed a new semi-quantitative staging system to categorise the severity of PSP pathology, using the distribution of tau aggregates as it progresses from subcortical to cerebellar and cortical regions. Here, we test the new PSP pathology staging system in an independent series of PSP, and test the potential association between pathology stage and clinical severity at death. We include tissue from 35 people with a clinical diagnosis of PSP (including N=25 with Richardson’s syndrome and N=10 with other phenotypes). Donors had attended longitudinal clinical studies at the Cambridge Centre Parkinson-plus including assessment of clinical severity by the PSP rating scale (PSPRS) and cognitive performance by the revised Addenbrooke’s Cognitive Examination (ACE-R). We rated tau pathology from none-to-severe in six regions. We focused on (I) astrocytic tau inclusions in striatum, frontal and occipital regions, and (II) neuronal and oligodendroglia tau inclusions in globus pallidus, subthalamic nucleus, and cerebellum. Thirty-two cases (91%) readily conformed to the new staging system, ranging from stage 2 to 6. Staging system applied to brains from people with different clinical phenotypes of PSP. Neuropathology stages correlated with clinical severity at death using both PSPRS and ACE-R, weighted for the interval between last assessment and donation. Our study supports the proposed sequential distribution of tau aggregates in PSP pathology, and the hypothesised relationship between clinical and neuropathological severity. For future studies, in order to standardise rating between centres, we propose a set of operational criteria for region-specific thresholds or tau burden, and a visual guide.