Quantitative susceptibility mapping in atypical Parkinsonisms

Background and purpose: Differential diagnosis between Parkinson's disease (PD) and Atypical Parkinsonisms, mainly Progressive Supranuclear Palsy (PSP) and Multiple System Atrophy (MSA), remains challenging. The low sensitivity of macroscopic findings at imaging might limit early diagnosis. The availability of iron-sensitive MR techniques and high magnetic field MR scanners provides new insights in evaluating brain structures in degenerative parkinsonisms. Quantitative Susceptibility Mapping (QSM) allows quantifying tissue iron content and could be sensitive to microstructural abnormalities which precede the appearence of regional atrophy. We measured the magnetic susceptibility (chi) of nigral and extranigral regions in patients with PD, PSP and MSA to evaluate the potential utility of the QSM technique for differential diagnosis. Materials and methods: 65 patients (36 PD, 14 MSA, 15 PSP) underwent clinical and radiological evaluation with 3 T MRI. QSM maps were obtained from GRE sequences. ROI were drawn on substantia nigra (SN), red nucleus (RN), subthalamic nucleus (STN), putamen, globus pallidus and caudate. chi values were compared to detect intergroup differences. Results: The highest diagnostic accuracy for PSP (area under the ROC curve, AUC, range 0.9-0.7) was observed for increased chi values in RN, STN and medial part of SN whereas in MSA (AUC range 0.8-0.7) iron deposition was significantly higher in the putamen, according to the patterns of pathological involvement that characterize the different diseases. Conclusion: QSM could be used for iron quantification of nigral and extranigral structures in all degenerative parkinsonisms and should be tested longitudinally in order to identify early microscopical changes.