Abstract

Background: Olfactory dysfunction is frequent in both Alzheimer’s Disease (AD) and Parkinson’s disease.
Objective: To examine whether the coexistence of parkinsonism in patients with Mild Cognitive Impairment (MCI) or mild AD synergistically affects olfactory impairment.
Methods: Olfaction was evaluated in three patient groups and age-matched controls. The patient groups consisted of amnestic MCI (Mini–Mental State Examination (MMSE) ≥ 24) or mild AD (MMSE 20-23) without parkinsonism (n: 64), parkinsonism free of cognitive impairment (n: 62), and MCI or mild AD with parkinsonism (n: 70). The odor-stick identification test for Japanese (OSIT-J) was used to count the numbers of correct answers, responses of indistinguishable, and responses of odorless (anosmia). Cognitive function was evaluated by MMSE, Clinical Dementia Rating Scale, NIA–AA criteria, MRI, and ¹²³I-IMP SPECT. Parkinsonism was diagnosed using the Unified Parkinson Disease Rating Scale (UPDRS)-III and ¹²³I-FP-CIT dopamine transporter SPECT.
Results: MCI or mild AD with parkinsonism group had a significantly lower percentage of correct answers than did MCI or mild AD without parkinsonism group (p: 0.0045) or parkinsonism group (p: 0.0015). The frequency of anosmia was significantly higher in MCI or mild AD with parkinsonism group than that in parkinsonism group (p: 0.0039). There were no significant differences in the number of responses of indistinguishable among the three patient groups (p>0.05). All the olfactory categories on the OSIT-J in the three patient groups showed significantly worse scores than did the age-matched controls (p<0.01).
Conclusion: The coexistence of parkinsonism in MCI or mild AD may synergistically exacerbate olfactory impairment.

Keywords: Alzheimer’s disease; Coexistence; Mild cognitive impairment; Olfaction; Olfactory impairment; Parkinson’s disease; Parkinsonism; Synergistic effect