Quantitative assessment of subcortical atrophy and iron content in progressive supranuclear palsy and parkinsonian variant of multiple system atrophy

Abstract

It is a matter of debate whether increased brain iron levels are the cause or only the consequence of neurodegenerative process in degenerative parkinsonism. The aim of this study is to characterize disease-related changes in volumes and iron-related R2 values of basal ganglia and thalamus. 13 patients with progressive supranuclear palsy (PSP), 15 with a parkinsonian variant of multiple system atrophy (MSA-p), 29 with Parkinson's disease (PD), and 21 age-matched controls underwent 3-Tesla MRI. The R2 values and volumes were calculated for the selected subcortical structures (caudate nucleus, putamen, globus pallidus, and thalamus) using an automated region-based analysis. Voxel-based analysis was also performed to visualize a topographical correlation of R2 value and volume. The PSP group had significantly higher R2 values in globus pallidus and caudate nucleus (p < 0.05), whereas the MSA-p group had higher R2 values in putamen (p < 0.001) than PD and controls. The globus pallidus in PSP and the putamen in MSA-p were the most significant areas of atrophy to differentiate PSP, MSA-p and PD (AUC = 0.856, 0.832, respectively, p < 0.001). The R2 values in both structures increased in parallel with the extent of atrophy. They were negatively correlated with volumes in putamen (r = -0.777, p < 0.001) and globus pallidus (r = -0.409, p = 0.025) of MSA-p, and globus pallidus (r = -0.4, p = 0.043) of PSP. Voxel-based analysis identified higher R2 values in more severely atrophic sub-regions in these structures. We observed topographical differences of iron deposition as well as atrophy between MSA-p and PSP. Increased iron levels were related to the structural atrophy in basal ganglia. Our results imply that iron accumulation is likely an epiphenomenon of the degenerative process.