Ires Ghielen

181 English summary symptoms in PD. In chapter 2 we investigated the phenomenology of anxiety in PD by performing a principal component analysis on the items of the Beck Anxiety Inventory (BAI) in a sample of 294 PD patients to explore underlying symptom dimensions and to relate these to other motor and non-motor features. We showed that the BAI consists of one affective (clustering anxious cognitions and emotions) and four somatic symptom subscales (clustering physical symptoms). We found significant associations between the somatic subscales and motor and autonomic symptoms, as measured with the UPDRS-III and SCOPA-AUT, respectively. The affective subscale showed a significant association with depressive symptoms (as measured with the BDI), but no association with motor or autonomic symptoms. To investigate the generalizability of the findings in chapter 2, chapter 3 describes the replication of the principal component analysis in 123 PD patients that were referred for neuropsychiatric evaluation to a specialized neuropsychiatric outpatient department. Again, we found one affective and four somatic anxiety symptom subscales, and a strong association between anxiety and depression. In a post- hoc analysis, the score on the affective subscale showed equal predictive value as compared to the total BAI score in predicting whether or not patients received an anxiety disorder diagnosis through psychiatric evaluation. The associations of the subscales of the BAI with the BDI, UPDRS-III and SCOPA-AUT confirm the overlap of anxiety in PD with both depression and with motor and autonomic symptoms. The affective subscale might be used to screen for anxiety in order to eliminate somatic equivalents of anxiety that can also be interpreted as motor or autonomic PD symptoms. However, we do not recommend to disregard the somatic symptoms completely, and rather suggest to interpret anxiety symptoms in the context of motor symptoms, taking this overlap and interaction into consideration. To investigate whether the associations between motor symptoms and anxiety differed in strength between high- versus low-anxiety PD patients, we used an explorative network analysis to study these associations in chapter 4 . In the high- anxiety group, 316 PD patients were included, in the low-anxiety group, 253 PD patients were included. The high-anxiety PD patient network showed higher global strength. In spite of group differences in clinical and demographic characteristics, with the high-anxious group showing significantly worse motor and cognitive function, a higher age, and more female patients, the network comparison test did not show statistically significant differences in strength of the connections between motor and anxiety symptoms. Since associations between motor and anxiety symptoms are apparent in both groups, this shows that these symptoms are associated, even when patients have no to mild anxiety symptoms.