Objective: Investigating the association between olfactory dysfunction and connectometry patterns in UPSIT-matched prodromal and PD patients.

Background: Parkinson’s disease (PD) is a heterogeneous neurodegenerative disease mostly characterized with motor symptoms including resting tremor, rigidity, and bradykinesia. Prodromal PD (proPD) is a preclinical stage of disease, when signs and symptoms are existing, but insufficient to make the diagnosis of PD. proPD is principally recognized with RBD and olfactory impaiement. Olfactory dysfunction is measured though a non-invasive test known as University of Pennsylvania Smell Identification Test (UPSIT). Using PPMI database, we compared UPSIT-matched PD and proPD groups based on connectometry patterns and investigated whether the degree of olfactory impairment is correlated with microstructure abnormality in the brain of PD or ProPD patients.

Methods: Participants involved in this research were recruited from PPMI. A total of 18 PD patients and 17 ProPDs were recruited from baseline available diffusion tensor imaging (DTI) data from PPMI project. Participants in each category were matched in their sex, UPSIT and MOCA. Diffusion MRI connectometry was used to study the effect of UPSIT in PD and proPD. A multiple regression model was used to investigate correlation of UPSIT score with white matter QA, considering age, sex, RBD, MOCA, as covariates in the model.

Results: Individuals with proPD had significantly higher QA comparing with PD patients in two fibers, that is, middle cerebellar peduncle and right arcuate fasciculus. Also, following fibers had higher QA in individuals with PD in comparison to proPD patients: left inferior longitudinal fasciculus, left fronto-occipital fasciculus, right and left fornix, right corticospinal tract, and right and left cingulum. In ProPD patients, the connectometry analysis identified left and right subgenual cingulum, right inferior fronto-occipital fasciculus, left corticospinal tract, left parietopontine, left cortico thalamic, and body and splenium of corpus callosum have positive association related to UPSIT score.

Conclusions: Collectively, we demonstrated that there is a strong correlation between white matter QA in different fibers and the impairment of olfaction (lower UPSIT score). Thus, it is postulated that pathologic microstructure alternations may be at least partially involved in the initiation and progression of olfactory dysfunction in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/association-of-olfaction-dysfunction-with-brain-microstructure-in-prodromal-parkinson-disease/