Hybrid Tau-PET/MRI study: Quantitative susceptibility mapping in progressive supranuclear palsy and its correlation...

The atypical Parkinsonian disorder progressive supranuclear palsy (PSP) forms a diagnostic challenge, resulting in frequent misdiagnosis and delay in treatment. Although structural MRI can detect PSP signs at more advanced stages, emerging diagnostic tools such as tau-PET and quantitative susceptibility mapping (QSM) may allow for earlier detection. This exploratory study aimed to investigate differences in QSM data of patients with PSP and healthy controls (HCs) and for the first time assess possible correlations between QSM and tau-PET data in patients with PSP to explore the relationship between tau aggregation and iron susceptibility.

We retrospectively investigated differences in susceptibility values of brain structures, as assessed by QSM, between 11 HCs and 31 patients with PSP [Richardson's syndrome (PSP-RS): n = 14; other subtypes (PSP-nonRS): n = 17]. Additionally, we examined co-registered [¹⁸F]PI-2620 PET and QSM data in the 31 patients with PSP to explore the relationship between tau accumulation and susceptibility changes.

Compared to HCs, patients with PSP showed higher QSM values in left nucleus caudate (p = 0.04) and bilateral dentate nucleus (p = 0.04, p = 0.01). Patients with the subtype PSP-RS showed higher QSM values than HCs in left dentate nucleus (p = 0.02). The association between the patients' QSM and tau-PET data showed a significant positive correlation.

These results suggest distinct patterns of regional iron accumulation in patients with PSP and its subtypes and support an association between iron and tau pathology. The data encourage further investigation in longitudinal studies and validation in larger cohorts to examine the value of QSM as a possible diagnostic biomarker.