Does Midbrain Atrophy Distinguish Progressive Supranuclear Palsy from Frontotemporal Dementia?

Background: The diagnostic value of midbrain atrophy for distinguishing behavioral variant frontotemporal dementia (bvFTD) from progressive supranuclear palsy (PSP) is unclear. Objective: To investigate whether measures of midbrain atrophy differentiate PSP from bvFTD. Methods: We included four groups: healthy controls (n = 19), PSP-Richardson syndrome (n = 20), bvFTD (n = 19) and Parkinson's disease (PD; n = 12). The following quantitative and qualitative measures were calculated: Hummingbird sign rating scale [HBS-RS], global midbrain atrophy [GMA], midbrain area, midbrain/pons ratio, the Magnetic Resonance Parkinsonism Index (MRPI), the MRPI 2.0 and brainstem volume. Results: Compared to controls, PSP and bvFTD had lower values of midbrain area, HBS-RS and GMA, and higher MRPI and MRPI 2.0. HBS-RS, GMA, midbrain/pons ratio, midbrain area, MRPI, MRPI 2.0 and brainstem volume distinguished PSP from bvFTD with 73%, 67%, 75%, 83%, 71%, 69% and 82% accuracies, respectively. Conclusions: Both quantitative and qualitative measures of midbrain atrophy provided modest accuracy in distinguishing PSP from bvFTD.