Annual percentage change of MR Parkinsonism index in progressive supranuclear palsy: a feasibility study

Considerable evidence suggests that midbrain-based magnetic resonance Parkinsonism index (MRPI) measurements are reliable biomarkers for the diagnosis of progressive supranuclear palsy (PSP). However, the longitudinal atrophy pattern of PSP and potential differences in change rates among PSP phenotypic spectrum remain unclear. This study aims to investigate the longitudinal changes of MRPI measurements and explore their potential role in PSP phenotype progression monitoring.

Thirty-six patients with PSP-Richardson's syndrome (PSP-RS), 21 patients with variant PSP (vPSP), and 21 healthy controls (HCs) with longitudinal MRI and clinical follow-up were enrolled. Midbrain-based morphometric measurements and the corresponding annual percentage changes (APCs) were measured and further used to evaluate the associations with disease progression.

Significant differences in midbrain-based morphometric biomarkers were observed both at baseline and longitudinal trajectories between PSP and HC groups, but no significant differences were found between PSP-RS and vPSP subgroups. Baseline comprehensive measurements were significantly associated with the baseline PSP rating scale (PSPrs) in all PSP and PSP phenotypes. The APC of MRPI was significantly associated with the APC of PSPrs in all PSP (r = 0.267, p = 0.046) and the PSP-RS subgroup (r = 0.386, p = 0.020).

This study characterizes the longitudinal atrophy trajectory of PSP phenotypes and the significant associations between morphometric measurements and disease severity. Dissecting the causal associations among core 4R-tau, dopamine, and subsequent atrophy trajectories may enhance the application of these biomarkers for phenotype attribution.

Questions The use of midbrain-based MRPI measurements to assess the longitudinal prognosis of the PSP phenotype remains uncertain. Findings Significant differences in midbrain-based morphometric biomarkers were observed both at baseline and longitudinal trajectories between PSP and health control groups. Clinical relevance Midbrain-based morphometric measurements hold promise as potential radiological biomarkers for monitoring PSP disease progression and assessment.