Diffusion tensor image analysis along the perivascular space and quantitative susceptibility mapping in the diagnosis and severity assessment of Parkinson's disease.

Background: Increased iron accumulation measured by quantitative susceptibility mapping (QSM) has been observed in various brain regions, especially substantia nigra (SN), in Parkinson's disease (PD). Glymphatic dysfunction evaluated by diffusion tensor image analysis along the perivascular space (DTI-ALPS) in PD has also attracted much attention recently. This study aimed to compare and combine DTI-ALPS and QSM of SN in the diagnosis and severity assessment of PD. Methods: As a case-control study, we retrospectively recruited 60 PD patients and 60 matched healthy controls. The DTI-ALPS index, QSM of SN, and their combination were calculated and further compared between the two groups. Receiver operating characteristic (ROC) curves were used to assess the diagnostic performance. We further analyzed the correlation of the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III score with DTI-ALPS and QSM of SN. Results: The average DTI-ALPS was significantly lower, whereas the average QSM of bilateral SN was significantly higher in PD [median (interquartile range): 1.38 (1.26-1.53); 0.09 (0.07-0.10)] compared to healthy controls [1.52 (1.41-1.71), P<0.001; 0.08 (0.07-0.09), P=0.020]. The combination showed a significantly higher area under the curve (AUC) of 0.801 than that of DTI-ALPS (0.729) or QSM of SN (0.624) in discriminating PD from healthy controls. Moreover, the average QSM of bilateral SN showed significant correlations with the MDS-UPDRS III score (rho =-0.276, P=0.034). Conclusions: DTI-ALPS and QSM of SN are potential biomarkers for the diagnosis and severity assessment of PD. The combination of them may improve the diagnostic performance.