Parkinson’s disease and chemosensory function: the relation with mild cognitive impairment and the single cognitive domain dysfunction

Mild cognitive impairment (MCI) and olfactory dysfunction are non-motor symptoms of Parkinson’s disease (PD), but their association is unclear. We investigated if MCI and the involvement of single cognitive domains might influence olfaction and taste in PD. The role of demographic, clinical and neuropsychiatric variables was assessed. We recruited fifty PD patients without dementia, no other reasons for cognitive impairment and no condition influencing evaluation of cognition, olfaction and taste. Every patient underwent a full neuropsychological and chemosensory (i.e., olfaction and taste) test battery with the Sniffin’ Sticks Extended test (SSET), Whole Mouth test (WMT) and Taste Strips test (TST). Fifty age- and sex-matched healthy subjects served as controls. Olfactory function and sweet identification were worse in PD than controls. MCI negatively influenced odor identification. Age, overall cognition, apathy and visuospatial dysfunction negatively influenced SSET score. Sour identification was affected by MCI and executive dysfunction, and salty identification by executive dysfunction. MCI, age and executive dysfunction worsened TST score. Awareness of olfactory dysfunction was impaired in PD with MCI. Education positively influenced SSET and TST scores. MCI and the dysfunction of some cognitive domains (i.e., executive, visuospatial) was associated with worse chemosensory function, suggesting shared pathology between these non-motor symptoms. Future studies should incorporate neuroimaging and cerebrospinal fluid data to confirm this hypothesis. SSET odor identification and TST sour identification could be explored as quick screening tests for PD-MCI. Funding: this research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.