Objective: To use a multimodal MRI approach for differential diagnosis of patients with degenerative parkinsonisms, comparing the diagnostic accuracy of Quantitative Susceptibility Mapping (QSM) data with morphometric indexes.

Background: MRI morphometric indexes were developed to differentiate Parkinson’s disease (PD) and atypical parkinsonisms (mainly Multiple System Atrophy -MSA- and Progressive Supranuclear Palsy -PSP). The pons-to-midbrain ratio (P/M) and the Magnetic Resonance Parkinsonism Index (MRPI) showed high diagnostic accuracy, but early diagnosis remains challenging. Iron-sensitive MRI techniques, as QSM, have recently shown encouraging diagnostic potential.

Method: One hundred consecutive outpatients of the Movement Disorders Center of Pisa were enrolled. They had a clinical diagnosis of probable PD (38), MSA (20, 12 p-MSA and 8 c-MSA) or PSP (42, 26 PSP-Richardson’s Syndrome-RS and 16 PSP non-RS phenotype). Each patient underwent a clinical evaluation and a 3T Brain MRI. The MRI protocol included T1-weighted and 3D multi-echo T2*-weighted sequences. The magnitude and phase data were processed and one quantitative magnetic susceptibility map was generated for each patient. The morphometric indexes P/M and MRPI were manually calculated on T1-weighted images. Magnetic susceptibility of selected regions was analysed drawing ROIs on substantia nigra (SN), red nucleus (RN), subthalamic nucleus (STN), globus pallidus, caudate and putamen.

Results: Morphometric evaluation was possible in all patients whereas QSM were obtained in 88 cases.
The 3-group comparison showed significant differences (p<0.001) in P/M, MRPI and susceptibility values of SN, RN, STN and putamen.
Morphometric indexes and magnetic susceptibility of RN showed high diagnostic accuracy in differentiating PD from PSP, especially when considering only the PSP-RS subgroup (in this scenario the accuracy of QSM and MRPI were comparable and had AUC = 0.959). Morphometric indexes did not show significant differences between PD and p-MSA whereas magnetic susceptibility of RN and putamen was able to differentiate the two groups (p=0.005).
Optimal cut-off values were determined to evaluate concordance, which ranged from good to moderate

Conclusion: Our results confirm the potential of morphometric and quantitative methods, supporting the use of multimodal MRI in the diagnostic phase of degenerative parkinsonisms.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/quantitative-susceptibility-mapping-for-differential-diagnosis-of-degenerative-parkinsonisms-a-comparison-with-morphometric-indexes/