Introduction: Neuromelanin-sensitive (NM) magnetic resonance imaging visualizes dopaminergic neuronal loss in the substantia nigra pars compacta (SNc) in Parkinson's disease (PD), and may be a useful diagnostic marker

Methods: Fifty-five patients with early stage PD and 12 age-matched healthy volunteers (HV) underwent 3T MR scanning. SNc volumes were determined according to the threshold of background signal intensity+3SD. SNc volumes were also compared between HV and three PD sub-groups as divided by UPDRS 3 scores with tertile calculations, using analysis of covariance (ANCOVA), adjusting by regional volumes and age.

Results: PD patients showed marked reductions of SNc volumes compared to HV (p<0.001). Within the PD group, nigral volume reductions were consistent for clinical laterality (p<0.05). Nigral volumes inversely correlated with UPDRS 3 (p<0.01), and were lowest in PD patients in the worst tertile for motor severity, compared to the more mildly affected PD cases (p<0.05) and HV groups (p<0.001).

Discussion: Our results confirm that NM-sensitive MR imaging helps distinguish early PD from healthy volunteers. In addition, the significant relationship between nigral volume and motor severity suggests that the method could be developed as a disease biomarker.