We evaluate quantitative susceptibility mapping (QSM) as an MRI technique to measure brain iron accumulation in Parkinson’s disease (PD) patients in different stages compared to healthy controls.

Brain iron deposition is involved in PD pathogenesis. QSM emerges as a non-invasive technique to quantify brain iron. However, the correlation of brain iron accumulation in the substantia nigra and other brain nuclei is not well-established in different stages of the disease.

We conducted a cross-sectional analysis of MRI scans from 78 patients with idiopathic PD (n=16 Hoehn and Yahr (H&Y) stage I, n=39 stage II, n=23 stage III&IV) and 31 healthy controls. We analyzed substantia nigra (SN), red nucleus (RN), caudate, putamen, and globus pallidus on the QSM-processed images to obtain the magnetic susceptibility values.

We found a higher accumulation of iron in the SN of PD patients in all stages versus controls (175.12±45.15ppb stage I vs. 180.89±44.77ppb stage II vs. 189.76±58.66ppb stage III&IV vs. 115.93±29.47ppb control; P<0.001), with no statistically significant difference within PD stages.  Iron in the RN was statistically significantly increased only in stage II versus controls (132.68±37.14ppb vs. 105.80±27.48ppb; P=0.0087). The iron levels in caudate, putamen, and globus pallidus were not different between any PD groups and controls.

QSM can measure iron in the basal ganglia of PD patients. Our data suggest brain iron accumulation occurs early in the disease course and only in the SN and RN of these patients. Neuromelanin, a natural chelator of iron in the SN, could account for the lack of increase of iron in advanced PD stages. This is a large cross-sectional study of brain iron deposition in PD according to H&Y staging. Prospective studies are warranted to further validate QSM as a method to measure brain iron, which could serve as a disease biomarker.