Is either anosmia or constipation associated with cognitive dysfunction in Parkinson's disease?

Objective To clarify the association of anosmia or constipation with cognitive dysfunction and disease severity in patients with Parkinson's disease (PD). Methods Newly diagnosed patients with PD (less than 5 years) without a clinical diagnosis of dementia were included from February 2017 to August 2018. The subjects were further divided into subgroups based on whether anosmia occurred and the grade of constipation. The severity of PD motor symptoms was rated using the Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (MDS-UPDRS), and cognitive functions were evaluated by Montreal Cognitive Assessment (MoCA). Statistical analyses including t-tests, chi-square tests, multiple linear regression, and binary logistic regression were used to determine statistical significance. Results A total of 107 newly diagnosed PD patients were included in this study. The MoCA score was significantly lower in the anosmia group (p < 0.001). Constipation was associated with impaired olfaction in a post-hoc test. The correlation coefficient between MoCA and UPSIT score was 0.41 (p < 0.001). Total anosmia and age were associated with cognitive dysfunction (MoCA < 26) (odds ratio, 2.63, p = 0.003; 1.10, p < 0.001, respectively). The anosmia group had a higher MDS-UPDRS part 3 score with beta coefficient of 7.30 (p = 0.02). Furthermore, grade 3 constipation was associated with a higher MDS-UPDRS total score with beta coefficient of 14.88 (p = 0.02). Conclusions Anosmia but not constipation was associated with cognitive impairment in PD patients. Nevertheless, severe constipation was associated with impaired olfaction and PD disease severity. We suggest that the propagation of alpha -synuclein from the olfactory route is distinct from the enteric nervous system, but the intercommunication between these two routes is complex.