Progressive supranuclear palsy: clinicopathological concepts and diagnostic challenges.

Progressive supranuclear palsy (PSP) is a clinical syndrome comprising supranuclear palsy, postural instability, and mild dementia. Neuropathologically, PSP is defined by the accumulation of neurofibrillary tangles. Since the first description of PSP in 1963, several distinct clinical syndromes have been described that are associated with PSP; this discovery challenges the traditional clinicopathological definition and complicates diagnosis in the absence of a reliable, disease-specific biomarker. We review the emerging nosology in this field and contrast the clinical and pathological characteristics of the different disease subgroups. These new insights emphasise that the pathological events and processes that lead to the accumulation of phosphorylated tau protein in the brain are best considered as dynamic processes that can develop at different rates, leading to different clinical phenomena. Moreover, for patients for whom the diagnosis is unclear, clinicians must continue to describe accurately the clinical picture of each individual, rather than label them with inaccurate diagnostic categories, such as atypical parkinsonism or PSP mimics. In this way, the development of the clinical features can be informative in assigning less common nosological categories that give clues to the underlying pathology and an understanding of the expected clinical course.