Scales to evaluate psychosis in Parkinson's disease.

Hallucinations and psychotic behaviors are a frequent non-motor aspect of Parkinson's disease and its treatment. These behaviors usually do not occur in the presence of the physician and are therefore difficult to rate. Further, because of their bizarre nature, hallucinations are frequently underreported by patients, and caregivers are often unaware of them until they become problematic. A number of scales have been developed for rating these behaviors, most of them borrowed or adapted from assessment tools used in other psychotic disorders like schizophrenia. In the latter disorders, however, hallucinations and psychosis are phenomenologically different than the typical hallucinations of Parkinson's disease. The Movement Disorder Society Task Force on Parkinson's Disease Rating Scales has completed a systematic critique of scales used in clinical trials focusing on hallucinations and psychosis. In this critique, the following scales met the criteria to be classified as Recommended: Neuropsychiatric Inventory, Brief Psychiatric Rating Scale, Positive and Negative Syndrome Scale, and Schedule for Assessment of Positive Symptoms. However, the Task Force felt that each of these scales has significant weaknesses and is insufficient to be considered a definitive rating tool. The Task Force officially recommended the development of a new scale to assess hallucinations and psychosis in Parkinson's disease. This effort is now ongoing with official endorsement by the Movement Disorder Society.