Neuropsychiatric symptoms and their impact on cognitive functioning in patients with parkinson's disease: A systematic review of the literature

Parkinson's disease (PD) is a progressive, neurodegenerative disorder that affects the dopaminergic system and is characterized by motor and nonmotor symptoms, which affect the quality of life. Among these, neuropsychiatric symptoms (NPS), such as depression, hallucinations, and apathy, are common and can accelerate cognitive decline. Although the association between some specific NPS (e.g., apathy) and cognitive functions has been investigated, no review has systematically examined the relationship between the whole of NPS and cognitive functions in PD patients without dementia. Therefore, the purpose of this study was to analyze the relationship between NPS taken together and cognitive impairment in patients with PD. According to the PRISMA-Statement, this systematic review critically examined the difference in cognitive performance between patients diagnosed with idiopathic PD with and without NPS. Results were classified according to the cognitive domain evaluated. Eleven studies met the eligibility criteria. The results showed that PD patients with NPS showed impaired performance on cognitive tasks compared with those without NPS, as well as in longitudinal studies. These results were also confirmed when the different domains were considered separately. Despite the limited number of included studies, the importance of assessing NPS in their totality rather than individual behavioral symptoms emerges. Clinical manifestations may vary among individuals and across different stages of the disease. Therefore, assessing the presence of these symptoms and the timing of their onset would be appropriate and may give the clinician important insights into the possible course and management of the disease.