Ires Ghielen

14 Chapter 1 implication of the replicated findings, we additionally performed a post-hoc analysis in which we investigated the predictive value of the principal component with the highest percentage of explained variance in whether or not patients received an anxiety disorder diagnosis. Chapter 4 compares two symptom networks of anxious versus non-anxious PD patients, including anxiety and motor symptoms. We investigated whether anxiety and motor symptoms are more strongly connected in the anxious PD patient sample, compared to the non-anxious PD patient sample [Ghielen et al., 2020 (submitted)]. To test this hypothesis, we performed a network comparison test. The previous chapters demonstrate relationships between anxiety and motor symptoms. However, no conclusions can be drawn concerning their relationships over time. Therefore, in chapter 5 , we investigate the longitudinal associations between anxiety, fear of falling, and freezing of gait in PD [Ghielen et al., 2020]. In addition, we investigated which confounding factors influenced these associations, to gain further understanding of these relationships. Part 2 To explore the current state of psychological treatment options, we describe two meta-analyses in which we investigated the effects of cognitive behavioral and mindfulness-based therapies on psychological distress in patients with neurodegenerative disorders in chapter 6 [46]. Since evidence for the treatment of anxiety in PD patients is extremely limited, and motor and non-motor symptoms appear to interact, especially in PD patients that experience symptom fluctuations, effective psychological treatment, especially multidisciplinary treatment is warranted [8, 13, 14]. Therefore, we developed a new intervention that combines acceptance and commitment therapy with physical therapy, to treat both non-motor and motor symptoms, including their interactions. In this treatment, we included PD patients that experience wearing- off related anxiety. Chapters 7 & 8 describe the study protocol and subsequent results of a pilot randomized controlled trial in which we describe and investigate the effectiveness and feasibility of this new body awareness treatment (named BEWARE ) [51, 52]. Finally, in chapter 9 , a summary is provided of the main findings of this thesis, followed by a general discussion and directions for future research.