Olfaction and taste in Parkinson's disease: the association with mild cognitive impairment and the single cognitive domain dysfunction

Mild cognitive impairment (MCI) and chemosensory dysfunction are non-motor symptoms of Parkinson's disease (PD), but their association is unclear. We explored if MCI and the involvement of single cognitive domains influence olfaction and taste in PD. The role of demographic, clinical and neuropsychiatric variables was tested. We recruited 50 PD patients without dementia, no other reasons for cognitive impairment, no condition that could influence evaluation of cognition, olfaction and taste. They underwent a full neuropsychological and chemosensory (i.e., olfaction and taste) test 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. Factors associated with poor olfactory function were age, overall cognition, apathy, and visuospatial dysfunction. 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. Our data confirmed that olfaction is abnormal in PD, while taste was only slightly impaired. Olfaction was worse in PD patients with visuospatial dysfunction, while sour and salty identification was worse in those with MCI and executive dysfunction, suggesting different underlying anatomical abnormalities. 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.