Differential Progression of Midbrain Atrophy in Parkinsonism: Longitudinal MRI Study.

AIMS To elucidate different patterns of progression of midbrain atrophy in patients with Richardson's syndrome (RS), progressive supranuclear palsy-parkinsonism (PSP-P), and Parkinson's disease (PD) using magnetic resonance imaging (MRI)-based visual rating indexes. METHODS We recruited 12 patients with PSP-RS, 12 with PSP-P, and 23 with PD for whom MRIs had been followed up for at least 2 years (mean ± SD, 4.9 ± 1.6 years) after the initial MRI. MRI-based visual rating indexes were used to estimate midbrain atrophy, including the ratio of the pontine to midbrain tegmental areas (P/M ratio) on a midsagittal image, the length between the interpeduncular fossa and the center of the cerebral aqueduct at the midmammillary-body level (MTEGM) on axial images, and the morning glory sign. RESULTS Initially, there were no differences in MRI-based visual rating indexes between PSP-P and PD, while PSP-RS showed a higher P/M ratio and lower MTEGM compared with PSP-P and PD. In PD, the P/M ratio and MTEGM remained stable with disease progression. However, the extent of changes between initial and follow-up indexes was similarly greater for both PSP-RS and PSP-P than for PD. Finally, PSP-P showed a higher P/M ratio and lower MTEGM compared with PD in the follow-up, while PSP-RS still exhibited the most profound changes. CONCLUSIONS Midbrain atrophy progresses differentially in patients with PSP-RS, PSP-P, and PD. Longitudinal measurements of midbrain atrophy using MRI-based visual rating indexes can help distinguish patients with PSP-P from those with PSP-RS and PD.