Sonja Rutten

Parkinson's disease (PD) is a neurodegenerative disorder affecting 1,350 per 100,000 Dutch people. The disease is best known for its characteristic movement complaints or motor symptoms: tremor, stiffness, slowness, impaired balance, and a decrease in spontaneous movements and facial expression. However, the disease is also accompanied by a range of non-motor symptoms, such as disorders of the autonomic nervous system, cognitive functioning, sleep, and psychological functioning.

Psychiatric disorders that occur in Parkinson's disease include psychosis, apathy, anxiety disorders, depression, and impulse control disorders. These conditions are caused by a combination of biological, social, and psychological factors. Biological factors also play an important causal role, including changes in neurobiological processes and disruptions to the circadian system, which coordinates our internal biorhythms with the 24-hour cycle of society.

Many Parkinson's patients suffer from sleep issues ranging from daytime sleepiness to insomnia. About one-third of patients develop an anxiety disorder and 17% depression. These symptoms have a major negative impact on quality of life for both patients and caregivers. This thesis aims to gain insight into these symptoms and their interrelationships, while also exploring non-pharmacological treatment options like light therapy.

Chapter 2 found that anxiety in PD consists of both somatic and affective dimensions. Affective subscales may be more accurate as they aren't influenced by physical 'noise'. Chapter 3 identified four predictors of anxiety: depression, impulse control issues, cognitive dysfunction, and REM sleep behavior disorder. Chapter 4 established that the relationship between insomnia and anxiety/depression is bidirectional, potentially creating a negative spiral.

Part 2 focuses on treatment. Chapter 5's meta-analysis shows that psychological interventions like CBT and mindfulness have modest positive effects on distress. Chapter 6 explores the theoretical background of light therapy as a way to restore circadian rhythms. Chapter 7 reports a randomized trial of Spectramax light therapy, which showed improvements in quality of life and non-motor symptoms, although the effect on overall PD severity wasn't statistically significant. Chapters 8 and 9 describe a trial for depression, finding that while both light and control groups improved, light therapy was specifically effective in improving sleep quality and reducing cortisol levels. Chapter 10 concludes that a holistic, multidisciplinary approach is essential for managing the multifactorial symptoms of Parkinson's disease.