Imaging of the nigrostriatal system for evaluating the preclinical phase of Parkinson's disease development: the utility of neuromelanin, diffusion MRI, and DAT-SPECT

Objective: To assess the utility of examining the nigrostriatal system with MRI and dopamine transporter (DAT) imaging for evaluating the preclinical phase of Parkinson’s disease (PD). Methods: The subjects were 32 patients with early PD and a history of probable rapid eye movement sleep behavior disorder (RBD; PD group), 15 patients with idiopathic RBD (RBD group), and 24 age-matched healthy controls (HC group) who underwent neuromelanin and diffusion tensor MRI for analysis of the substantia nigra pars compacta (SNpc). The RBD and PD groups underwent DAT imaging. In the RBD group, totals of 39 MRI and 27 DAT imaging examinations were obtained longitudinally. For each value, intergroup differences and receiver operating characteristic analysis for diagnostic performance were examined statistically. Results: The neuromelanin value was significantly lower and the diffusion tensor values except fractional anisotropy were significantly higher in the RBD and PD groups than in the HC group. The DAT specific binding ratio (SBR) was significantly lower in the PD group than in the RBD group. The areas under the receiver operating characteristic curves (AUCs) for neuromelanin/mean diffusivity value in the SNpc were 0.76/0.82 for diagnosing RBD and 0.83/0.80 for diagnosing PD. The area under the receiver operating characteristic curves for the SBR for discriminating PD from RBD was 0.87. Conclusion: MRI and DAT imaging may be useful for evaluating sequential nigrostriatal changes during the preclinical phase of PD. Advances in knowledge: MRI detects nigrostriatal changes in both RBD and early PD, and DAT imaging detects nigrostriatal changes during the transition to PD in RBD.