Diffusion-weighted MRI differentiates the Parkinson variant of multiple system atrophy from PD

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.