Background and objective: The parkinson variant of multiple system atrophy (MSA-P) and progressive supranuclear palsy (PSP) present with atypical parkinsonism, which may be misdiagnosed as PD, particularly in early disease stages. It was previously shown that diffusion-weighted MRI (DWI) is a sensitive tool to discriminate MSA-P from PD based on increased apparent diffusion coefficients (ADCs) in the putamen. In this study DWI was evaluated in 10 patients with PSP compared with 13 patients with PD and 12 with MSA-P. Methods: Disease was diagnosed according to established diagnostic criteria and groups were matched for age, disease duration, and Hoehn and Yahr “off” stage. Regional ADCs (rADCs) were determined in different brain regions including basal ganglia, gray matter, white matter, substantia nigra, and pons. Results: In patients with PSP compared with those with PD, rADCs were significantly increased in putamen, globus pallidus, and caudate nucleus. Stepwise logistic regression analysis followed by receiver operating characteristics analysis identified an optimal cut-off value for putaminal rADC, discriminating PSP and PD with a sensitivity of 90% and a positive predictive value of 100%. DWI failed to discriminate PSP and MSA-P. Conclusions: These results show that DWI detects basal ganglia abnormalities in PSP patients within few years of disease onset, discriminating patients with PSP from those with PD, but not from those with MSA-P.

Objective and Background: Routine MRI as well as MR volumetry and MRS have been shown to contribute to the differential diagnosis of the Parkinson variant of multiple system atrophy (MSA-P) and PD. However, it is currently unknown whether diffusion-weighted imaging (DWI) discriminates these disorders. Methods: Ten patients with MSA-P (mean age, 64 years) were studied, 11 with PD (mean age, 64 years), and seven healthy volunteers (mean age, 59 years) matched for age and disease duration. Regional apparent diffusion coefficients (rADC) were determined in different brain regions including basal ganglia, gray matter, white matter, substantia nigra, and pons. Results: Patients with MSA-P had higher putaminal rADC (median 0.791 × 10³/mm²/s) than both patients with PD (median 0.698 × 10³/mm²/s, p < 0.001) and healthy volunteers (median 0.727 × 10³/mm²/s, p < 0.001). There were no significant differences in putaminal rADC between patients with PD and healthy volunteers. Moreover, none of the putaminal rADC values in the PD and control group surpassed the lowest value in the MSA-P group. There were no significant group differences in the rADC values in other brain regions such as pons, substantia nigra, globus pallidus, caudate nucleus, thalamus, or gray and white matter. Putaminal rADC values correlated significantly with Unified PD Rating Scale OFF scores in patients with MSA as measured by the Spearman rank test. Conclusion: DWI, even if measured in the slice direction only, is able to discriminate MSA-P and both patients with PD and healthy volunteers on the basis of putaminal rADC values. The increased putaminal rADC values in Parkinson variant of multiple system atrophy are likely to reflect ongoing striatal degeneration, whereas most neuropathologic studies reveal intact striatum in PD. Diffusion-weighted imaging may represent a useful diagnostic tool that can provide additional support for a diagnosis of Parkinson variant of multiple system atrophy.