Olfactory function and apathy as potential biomarker in patients with Parkinson's disease

Introduction: Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor symptoms as bradykinesia, rigidity, tremor and postural instability. Additionally, PD is usually associated with non-motor symptoms (NMS) that include smell and taste dysfunctions, neuropsychiatric symptoms such as apathy, anxiety and cognitive impairment, sleep problems and autonomic dysregulation [1-2]. The aim of the study was first to investigate olfactory function, cognitive impairment, apathy and fatigue in PD patients in relation to healthy controls, and second to analyze the relationship between these NMS and the severity of motor symptoms in subjects with PD. Materials and methods: One hundred and forty-seven participants were enrolled (96 PD patients, mean age in years: 67.5, SD: 7.2; 51 healthy controls; mean age: 65.1, SD: 11.8). Olfactory function was evaluated using the Sniffin’ Sticks test. The Montreal Cognitive Assessment (MoCA) was used to assess cognitive impairment. Apathy was examined by the Starkstein Apathy Scale (SAS) and fatigue was evaluated by the Parkinson’s Disease Fatigue Scale (PFS). Results: PD patients showed severe impairment in olfactory function compared to healthy controls. Moreover, in PD patients apathy and fatigue scores were significantly increased, while MOCA scores were significantly decreased in comparison to controls. Multivariate linear regression analyses showed that both apathy and UPDRS were associated with olfactory function. Conclusion: Our results identified a greater level of apathy in PD patients affected by severe olfactory loss. Moreover, the present study confirms that alteration of olfactory parameters, such as odor threshold, identification, discrimination and TDI score, are related to other NMS. References: 1) Poewe, 2008. Mov Disord 26(1):6–17. 2) Scapira et al., 2017. Eur J Neurol 15(1):14–20.