This prospective observational study aimed to evaluate quantitative susceptibility mapping (QSM) as an imaging technique to measure brain iron accumulation in Parkinson’s Disease (PD) patients in different Hoehn and Yahr (H&Y) stages compared to healthy controls and subjects with REM sleep behavioral disorder (RBD).

Excessive brain iron deposition is involved in PD pathogenesis. However, the correlation of brain iron accumulation in various brain nuclei in different stages of the disease with levels of neuromelanin and dopaminergic degeneration is not well-established.

Median susceptibility increased significantly between healthy volunteers and PD Stage I patients in the SN and RN, as well as longitudinally in the SN. Susceptibility was significantly increased longitudinally only in the RBD patients and stage I PD patients in the SN. Longitudinal neuromelanin volume decreased in RBD and PD stage I patients. The PD subjects who progressed in stages had a 5% decrease in whole gray matter BP and a 10% decrease in putamen. BP did not change in the subjects who did not progress in H&Y stages.

QSM can measure brain iron in PD patients. Our data suggests iron accumulation occurs early in the disease course only in the substantia nigra and red nucleus of these patients and correlates with reduction in neuromelanin. Loss of dopamine correlated with clinical progression in PD patients.