Track density imaging in progressive supranuclear palsy: A pilot study

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by white matter (WM) changes in different supra‐ and infratentorial brain structures. We used track density imaging (TDI) to characterize WM microstructural alterations in patients with PSP‐Richardson's Syndrome (PSP‐RS). Moreover, we investigated the diagnostic utility of TDI in distinguishing patients with PSP‐RS from those with Parkinson's disease and healthy controls (HC). Twenty PSP‐RS patients, 21 PD patients, and 23 HC underwent a 3 T MRI diffusion‐weighted (DW) imaging. Then, we combined constrained spherical deconvolution and WM probabilistic tractography to reconstruct track density maps by calculating the number of WM streamlines traversing each voxel. Voxel‐wise analysis was performed to assess group differences in track density maps. A support vector machine (SVM) approach was also used to evaluate the performance of TDI for discriminating between groups. Relative to PD patients, decreases in track density in PSP‐RS patients were found in brainstem, cerebellum, thalamus, corpus callosum, and corticospinal tract. Similar findings were obtained between PSP‐RS patients and HC. No differences in TDI were observed between PD and HC. SVM approach based on whole‐brain analysis differentiated PD patients from PSP‐RS with an area under the curve (AUC) of 0.82. The AUC reached a value of 0.98 considering only the voxels belonging to the superior cerebellar peduncle. This study shows that TDI may represent a useful approach for characterizing WM alterations in PSP‐RS patients. Moreover, track density decrease in PSP could be considered a new feature for the differentiation of patients with PSP‐RS from those with PD.