Whole-Brain Atrophy Rate in Idiopathic Parkinson's Disease, Multiple System Atrophy, and Progressive Supranuclear Palsy

In multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), the absence of surrogate endpoints makes clinical trials long and expensive. We aim to determine annualized whole-brain atrophy rates (a-WBAR) in idiopathic Parkinson's disease (IPD), MSA, and PSP. Ten healthy controls, 20 IPD, 12 PSP, and 8 MSA patients were studied using a volumetric MRI technique (SIENA). In controls, the a-WBAR was 0.37% ± 0.28 (CI 95% 0.17-0.57), while in IPD a-WBAR was 0.54% ± 0.38 (CI 95% 0.32-0.68). The IPD patients did not differ from the controls. In PSP, the a-WBAR was 1.26% ± 0.51 (CI 95%: 0.95-1.58). In MSA, a-WBAR was 1.65% ± 1.12 (CI 95%: 0.71-2.59). MSA did not differ from PSP. The a-WBAR in PSP and MSA were significantly higher than in the IPD group (p = 0.004 and p < 0.001, resp.). In PSP, the use of a-WBAR required one-half of the patients needed for clinical scales to detect a 50% reduction in their progression. In MSA, one-quarter of the patients would be needed to detect the same effect. a-WBAR is a reasonable candidate to consider as a surrogate endpoint in short clinical trials using smaller sample sizes. The confidence intervals for a-WBAR may add a potential retrospective application for a-WBAR to improve the diagnostic accuracy of MSA and PSP versus IPD.