Differentiation of Parkinsonism-Predominant Multiple System Atrophy from Idiopathic Parkinson Disease Using 3T Susceptibility-Weighted MR Imaging,Focusing on Putaminal Change and Lesion Asymmetry

BACKGROUND AND PURPOSE:Asymmetric presentation of clinical feature in parkinsonism is common, but correlatable radiologic feature is not clearly defined. Our aim was to evaluate 3T susceptibility-weighted imaging findings for differentiating parkinsonism-predominant multiple system atrophy from idiopathic Parkinson disease, focusing on putaminal changes and lesion asymmetry.MATERIALS AND METHODS:This retrospective cohort study included 27 patients with parkinsonism-predominant multiple system atrophy and 50 patients with idiopathic Parkinson disease diagnosed clinically. Twenty-seven age-matched subjects without evidence of movement disorders who underwent SWI were included as the control group. A consensus was reached by 2 radiologists who visually assessed SWI for the presence of putaminal atrophy and marked signal hypointensity on each side of the posterolateral putamen. We also quantitatively measured putaminal width and phase-shift values.RESULTS:The mean disease duration was 4.7 years for the patients with parkinsonism-predominant multiple system atrophy and 7.8 years for the patients with idiopathic Parkinson disease. In the patients with parkinsonism-predominant multiple system atrophy, putaminal atrophy was frequently observed (14/27, 51.9%) and was most commonly found in the unilateral putamen (13/14). Marked signal hypointensity was observed in 12 patients with parkinsonism-predominant multiple system atrophy (44.4%). No patients with idiopathic Parkinson disease or healthy controls showed putaminal atrophy or marked signal hypointensity. Quantitatively measured putaminal width, phase-shift values, and the ratio of mean phase-shift values for the dominant and nondominant sides were significantly different between the parkinsonism-predominant multiple system atrophy group and the idiopathic Parkinson disease and healthy control groups (P < .001).CONCLUSIONS:3T SWI can visualize putaminal atrophy and marked signal hypointensity in patients with parkinsonism-predominant multiple system atrophy with high specificity. Furthermore, it clearly demonstrates the dominant side of putaminal changes, which correlate with the contralateral symptomatic side of patients.

Parkinsonism-predominant multiple system atrophy (MSA-p) is one of the Parkinson-plus syndromes that has a clinical manifestation similar to that of idiopathic Parkinson disease (IPD) and is often challenging to diagnose in its early stage. MR imaging plays a role in differentiating MSA-p from IPD and is included as an additional feature for the diagnosis of possible multiple system atrophy.¹ Various conventional and functional MR imaging findings regarding the putamen in MSA-p have been reported.^2–6 However, these findings had limited sensitivity and specificity.⁶An asymmetric presentation of clinical features is common for IPD in its early stage, while symmetric symptoms are more common in MSA-p than in IPD.^7,8 However, the clinical manifestation of parkinsonism develops asymmetrically in many patients with MSA-p, and it has been reported that approximately 40%–50% of patients with MSA-p present with initial asymmetric symptoms.^8,9 This presentation increases the difficulty of clinically differentiating IPD from MSA-p in the early stage of disease. However, to our knowledge, there are few previous reports that used imaging to examine the asymmetry of putaminal abnormalities in MSA-p.Susceptibility-weighted imaging (SWI), which was recently introduced and is now widely used in clinical brain imaging, reflects the physical magnetic properties of tissues because susceptibility changes in tissues, such as iron deposition, are very sensitive.¹⁰ In addition to the sensitivity of SWI to paramagnetic material, corrected phase images that are calculated to form final SWI can provide quantitative phase-shift values that reflect tissue iron content.¹¹ Recently published studies attempted to use SWI to differentiate movement disorders, including MSA-p,¹² and demonstrated different iron-deposition patterns between MSA-p and IPD by measuring phase-shift values by using corrected phase images of SWI sequences.¹³ However, most previous studies regarding SWI were performed on 1.5T or weaker main magnetic field MR imaging machines. When main magnetic field is increased to 3T, spins process at a higher frequency, which may result in phase shifts caused by susceptibility changes being more exaggerated on SWI.Thus, the purpose of the present study was to evaluate the imaging findings of 3T SWI for differentiating MSA-p from IPD, focusing on putaminal changes and lesion asymmetry.