Objective:  To evaluate different approaches of segmentation of the putamen in order to discriminate PD from MSA-P based on putaminal diffusion imaging.

Background: Differences in prognosis and therapy as well as research bias make an early discrimination between Parkinson’s Disease (PD) and the parkinsonian variant of multiple system atrophy (MSA-P) desirable. It has been shown that putaminal diffusion imaging represents a useful diagnostic tool to discriminate PD from MSA-P. Some studies were not able to confirm the role of putaminal diffusion imaging as suitable discriminator, however heterogeneity exists in the segmentation of the putamen across the studies. 

Methods: In this retrospective blinded study, putaminal mean diffusivity (MD) values of 115 study participants, including 61 patients with PD and 24 with MSA-P as well as 30 healthy controls (HC), were evaluated. Different approaches to define the region of interest (ROI) in the putamen were applied: we segmented the whole putamen and the putamen at the level of Foramen Monroi, and we also manually placed large and small circular ROIs in the anterior and posterior putamen. Diagnostic accuracy for each type of segmentation was estimated using receiver operating characteristics (ROC) analysis.

Results: Significantly increased putaminal MD values (univariate ANOVA with post-hoc Bonferroni correction: p < 0,001) were found in all but the small anterior ROI in MSA-P versus PD and HC. The ROC analyses revealed an area under the curve > 0,9 for the small ROI located in the posterior putamen (sensitivity 67%, specificity 100%), for the entire putamen (sensitivity 83%, specificity 97%) and for the putamen at Foramen Monroi level (sensitivity 88 %, specificity 96%). Discrimination was worse if ROIs were placed in the anterior part of the putamen.

Conclusions: This study shows that putaminal diffusion imaging enables to discriminate MSA-P from PD. However, the segmentation procedure seems to considerably influence the discriminative ability of this diagnostic tool. Best discrimination is reached either by placing a ROI in the posterior putamen, by segmenting the putamen as a whole, or by segmenting the putamen at the level of Foramen Monroi.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/putaminal-diffusion-imaging-for-the-differential-diagnosis-of-the-parkinsonian-variant-of-multiple-system-atrophy-from-parkinsons-disease-impact-of-segmentation-accuracy/