Olfactory anosognosia is a predictor of cognitive decline and dementia conversion in Parkinson's disease

ObjectiveParkinson's disease (PD) patients are often unaware of olfactory deficits despite having hyposmia from the early stages. We aimed to evaluate whether olfactory anosognosia is a predictor of cognitive decline in PD.MethodsIn this retrospective cohort study, we recruited 77 PD patients who underwent both olfactory and neuropsychological tests and were followed-up for over 5years. Based on the degree of olfactory dysfunction and awareness of its presence, patients were classified as normosmic patients (Normosmia group, n=15), hyposmic patients without olfactory anosognosia (Hyposmia-OA-, n=40), or hyposmic patients with olfactory anosognosia (Hyposmia-OA+, n=22). We compared the rates of cognitive decline using linear mixed model and dementia conversion using a survival analysis among the groups.ResultsA higher proportion of patients in the Hyposmia-OA+ group had mild cognitive impairment at baseline (77.3%) and dementia converter at follow-up (50.0%). The Hyposmia-OA+ group exhibited a faster decline in frontal executive and global cognitive function than did the Normosmia and Hyposmia-OA- groups. A Kaplan-Meier analysis demonstrated that the conversion rate to dementia was significantly higher in the Hyposmia-OA+ group than in the Normosmia (P=0.007) and Hyposmia-OA- (P=0.038) groups. A Cox regression analysis showed that olfactory anosognosia remained a significant predictor of time to develop dementia in the Hyposmia-OA+ group compared to the Normosmia group (adjusted hazard ratio 3.30; 95% confidence interval 1.10-8.21).ConclusionThis study suggests that olfactory anosognosia is a predictor of cognitive decline and dementia conversion in PD.