Psychosis in Parkinson's Disease.

Although illusions, hallucinations and delusions did not play a prominent role in James Parkinson's original clinical descriptions, the longitudinal view of disease progression he advocated has important lessons for the study of such symptoms today. A focus on longitudinal progression rather than individual symptoms led to the concept of PD psychosis-a spectrum of positive symptoms in Parkinson's disease. The publication of criteria for PD psychosis in 2007 helped unify the disparate set of symptoms, raising their profile and resulting in a rapid expansion of literature focussing on clinical aspects, mechanisms, and treatment. Here we review this literature and the evolving view of PD psychosis. Adding to previous evidence of a prospective risk for dementia and the move to supervised care, key recent developments include: recognition of prevalence increase with disease duration; a broadening of symptoms included in PD psychosis; better characterization of higher visual and cognitive dysfunction risk factors; structural, functional, and neurotransmitter imaging biomarker evidence; and approval of pimavanserin in the United States for the treatment of PD psychosis. The accumulating evidence raises novel questions and directions for future research that promise a better understanding of the clinical management of PD psychosis and its role as a biomarker for PD stage and progression.