Diffusion tensor tract-specific analysis of the uncinate fasciculus in patients with progressive supranuclear palsy

The uncinate fasciculus (UF), a major white-matter tract connecting the frontal and temporal lobes, is related to cognitive/behavioral function. Recently, the UF has been suggested to constitute an indirect pathway of the "semantic ventral pathway" in association with the inferior longitudinal fasciculus (ILF). This retrospective study aimed to evaluate damage to the UF and ILF in patients with progressive supranuclear palsy (PSP) using diffusion tensor tract-specific analysis.

Diffusion tensor imaging (DTI) of 16 PSP patients with Richardson's syndrome (PSP-RS) and 21 age-matched volunteers were obtained. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values for the bilateral UF and ILF were calculated by tract-specific analysis. Student's t test was used to evaluate the differences between the patients and controls. Also, voxel-based morphometry (VBM) was performed using 3D T1-weighted images to explore the regional atrophy of gray matter in the patients.

In patients with PSP-RS, FA of the left UF was significantly decreased compared with the controls, while significant increases in ADC were found in the UF and ILF bilaterally. VBM analysis showed significant clusters of reduced gray matter in the frontal cortex (predominantly in the lateral orbitofrontal cortex, pars opercularis and mesial frontal cortex) and subcortical nuclei (midbrain, caudate and thalamic).

This study has shown that patients with PSP-RS had impairment of the UF and ILF. Damage to the UF is thought to be related to atrophy of the orbitofrontal cortex and may possibly be correlated with the cognitive/behavioral impairment seen in PSP.