The clinical differential diagnosis between Parkinson's disease (PD) and progressive
supranuclear palsy (PSP) is often challenging. The description of milder PSP phenotypes
strongly resembling PD, such as PSP-Parkinsonism, further increased the diagnostic
challenge and the need for reliable neuroimaging biomarkers to enhance the diagnostic
certainty. This review aims to summarize the contribution of a relatively simple and
widely available imaging technique such as MR planimetry in the differential diagnosis
between PD and PSP, focusing on the recent advancements in this field. The development
of accurate MR planimetric biomarkers, together with the implementation of automated
algorithms, led to robust and objective measures for the differential diagnosis of
PSP and PD at the individual level. Evidence from longitudinal studies also suggests
a role of MR planimetry in predicting the development of the PSP clinical signs, allowing
to identify PSP patients before they meet diagnostic criteria when their clinical
phenotype can be indistinguishable from PD. Finally, promising evidence exists on
the possible association between MR planimetric measures and the underlying pathology,
with important implications for trials with new disease-modifying target therapies.
