"Parkinson's disease" on the way to progressive supranuclear palsy: a review on PSP-parkinsonism.

Progressive supranuclear palsy (PSP) is a progressive atypical parkinsonian syndrome characterised by postural instability, supranuclear ophthalmoplegia, dysarthria, dysphagia, executive dysfunction and other features. This clinical presentation represents the classic PSP-Richardson syndrome (PSP-RS). However, several other clinical subtypes have been recognised, including PSP-parkinsonism (PSP-P), probably the second most common PSP variant. Unlike PSP-RS, PSP-P often presents with an asymmetric onset, tremor and a moderate initial response to levodopa, especially during the first years of the disease, thus resembling Parkinson's disease (PD). It runs a more favourable course, but over time, PSP-P may evolve clinically into PSP-RS. Therefore, it may seem that PSP-P stands clinically between PD and PSP. There are several peculiarities that can distinguish PSP-P from these entities. As there is lack of systematic reviews on PSP-P in the literature, we decided to summarise all the necessary data about the epidemiology, clinical picture, neuroimaging, genetics and other aspects of this PSP variant in order to provide complete information for the reader.