Abstract
INTRODUCTION: While anxiety, depression and insomnia frequently (co-)occur in Parkinson's disease (PD) patients, little is known about their temporal relationship. In this study, we tested two hypotheses: i) insomnia predicts an increase in symptoms of depression or anxiety and ii) anxiety or depression at baseline predicts insomnia in PD patients six months later. METHODS: We used longitudinal data from a prospective cohort study of early-stage, medication-naïve PD patients. Primary outcome measures were: anxiety symptoms, measured with the State-Trait Anxiety Inventory (STAI); depressive symptoms, measured with the 15-item Geriatric Depression Scale (GDS-15); and insomnia, defined as a score ≥ 2 on item 1.7 of the Movement Disorder Society - Unified Parkinson's Disease Rating Scale. We performed linear and logistic regression analyses, correcting for baseline value of the respective outcome variable. RESULTS: Baseline insomnia was not associated with GDS-15 or STAI total score at follow-up. In a post hoc analysis, we found that insomnia predicted a higher STAI State score (B(SE) = 2.50 (1.07), p < 0.05), while the association with the STAI Trait score was not significant. Baseline STAI scores (B(SE) = 0.02 (0.01), p = 0.001) and GDS-15 score (B(SE) = 0.15 (0.05), p < 0.001) were significantly associated with insomnia at follow-up. CONCLUSION: Symptoms of anxiety and depression may constitute a risk factor for insomnia in PD. The relationship between insomnia and anxiety is bidirectional, which suggests that both anxiety and sleep disorders can start a negative spiral in PD patients, where one enhances the other. Independent clinical attention for these symptoms in PD patients is therefore warranted.