Track density imaging: A reliable method to assess white matter changes in Progressive Supranuclear Palsy with predominant parkinsonism

Introduction: Track density imaging (TDI) has been proven to be a useful approach able to investigate white matter (WM) anatomical integrity in several neurodegenerative conditions, such as Parkinson's disease (PD) and classical phenotype of Progressive Supranuclear Palsy (PSP) also known as Richardson's syndrome (RS). To the best of our knowledge, no studies have assessed WM changes in PSP-predominant parkinsonism (PSP-P) patients by using a TDI approach, and no studies have explored the potential role of these changes in discriminating patients with PSP-P from those with PSP-RS and PD. Methods: We used TDI to characterize WM changes in 31 PSP-P compared to 36 PSP-RS, 36 PD and 37 healthy controls (HC). Then, a support vector machine (SVM) approach was used to evaluate the performance of TDI in discriminating between patient groups. Results: Relative to HC and PD patients, decreased track density in PSP-P patients was found in several WM regions such as the midbrain, superior cerebellar peduncles, cerebellum and corticospinal tract. By contrast, higher values of track density were observed in PSP-P patients compared to PSP-RS. SVM approach using TDI differentiated patients with PSP-P from PD and PSP-RS with an area under the curve of 0.90 and 0.76, respectively. Conclusions: Our findings suggest that TDI may represent a useful approach for characterizing WM changes in PSP-P patients representing a potential new MRI biomarker in distinguishing this PSP phenotype from PD.