Changes of olfactory tract in Parkinson's disease: a DTI tractography study

Impaired olfactory function is one of the main features of Parkinson's disease. However, how peripheral olfactory structures are involved remains unclear. Using diffusion tensor imaging fiber tracking, we investigated for MRI microstructural changes in the parkinsonian peripheral olfactory system and particularly the olfactory tract, in order to seek a better understanding of the structural alternations underlying hyposmia in Parkinson's disease.

All patients were assessed utilizing by the Italian Olfactory Identification Test for olfactory function and the Unified Parkinson's Disease Rating Scale-III part as well as Hoehn and Yahr rating scale for motor disability. Imaging was performed on a 3 T Clinical MR scanner. MRI data pre-processing was carried out by DTIPrep, diffusion tensor imaging reconstruction, and fiber tracking using Diffusion Toolkit and tractography analysis by TrackVis. The following parameters were used for groupwise comparison: fractional anisotropy, mean diffusivity, radial diffusivity, axial diffusivity, and tract volume.

Overall 23 patients with Parkinson's disease (mean age 63.6 ± 9.3 years, UPDRS-III 24.5 ± 12.3, H&Y 1.9 ± 0.5) and 18 controls (mean age 56.3 ± 13.7 years) were recruited. All patients had been diagnosed hyposmic. Diffusion tensor imaging analysis of the olfactory tract showed significant fractional anisotropy, and tract volume decreases for the Parkinson's disease group compared with controls (P < 0.05). Fractional anisotropy and age, in the control group, were significant for multiple correlations (r = - 0.36, P < 0.05, Spearman's rank correlation).

Fiber tracking diffusion tensor imaging analysis of olfactory tract was feasible, and it could be helpful for characterizing hyposmia in Parkinson's disease.