Effect of Istradefylline Treatment on Behavioral Measures of Apathy in Parkinson's Disease.

Overview

Apathy is defined as a lack of feeling, emotion, interest, or concern. Apathy also involves reduction or loss of motivation and goal-directed behavior. Clinically significant apathy, where meaningful activities are given up and quality of life is diminished, is common in people with Parkinson's disease (PD). Many individuals with Parkinson's disease experiencing fluctuations in the severity of their movement problems and medication "off" time. "Off" time refers to periods of the day between doses of PD medication when your motor symptoms (e.g., tremor, stiffness, slowness, walking problems, etc.) are worse and interfere with your ability to complete tasks of daily living. The investigational drug, Istradefylline, is an FDA-approved medication to treat motor fluctuations and "off" time in PD. The purpose of this study is to investigate whether people with Parkinson's disease (PD) who are treated with istradefylline (ISD) show improvements in motivation and apathy over a 12-week period. Specifically, we wish to see whether people with PD who are treated with ISD engage in more physical and recreational activities, such as hobbies and other interests.

Apathy is a clinical syndrome characterized by lack of motivation, interest, engagement, and emotional reactivity for goal-directed behaviors (Starkstein et al., 2008). A common and troublesome symptom in Parkinson's disease (PD), apathy is associated with diminished quality of life for both the patient and care partner (Van Reekum, Stuss, \& Ostrander, 2005; Barone et al., 2009). To the extent that apathy reduces engagement in physical and social activities, it may also result in more rapid disease progression and cognitive decline (e.g., Crotty \& Schwarzchild, 2020). Addressing apathy is therefore a crucial component of treating PD. A recent open-label study demonstrated significant reduction in self-reported apathy with Istradefylline (ISD) in PD (Nagayama et al, 2019). This unsurprising result likely reflects contributions from known benefits of ISD with respect to daytime somnolence and improved motor functioning (Matsuura et al., 2017; Suzuki et al. 2017), as well as enhanced functioning of dopamine-mediated reward pathways. However, patients with PD advanced enough to warrant treatment with ISD may also have diminished insight and awareness, and therefore not be particularly reliable reporters (e.g., Orfei et al., 2018). It is also unknown whether and to what extent this is correlated with actual changes in behavior and caregiver burden. The objective of this study is to determine whether treatment with ISD increases engagement in physical and other meaningful activities in patients with Parkinson's disease.