Scales to assess psychosis in Parkinson's disease: Critique and recommendations

Psychotic symptoms are a frequent occurrence in Parkinson's disease (PD), affecting up to 50% of patients. The Movement Disorder Society established a Task Force on Rating Scales in PD, and this critique applies to published, peer-reviewed rating psychosis scales used in PD psychosis studies. Twelve psychosis scales/questionnaires were reviewed. None of the reviewed scales adequately captured the entire phenomenology of PD psychosis. While the Task Force has labeled some scales as "recommended" or "suggested" based on the fulfilling-defined criteria, none of the current scales contained all the basic content, mechanistic and psychometric properties needed to capture PD psychotic phenomena and to measure clinical response over time. Different scales may be better for some settings versus others. Since one scale may not be able to serve all needs, a scale used to measure clinical response and change over time [such as the Clinical Global Impression Scale (CGIS)] may need to be combined with another scale better at cataloging specific features [such as the Neuropsychiatric Inventory (NPI) or Schedule for Assessment of Positive Symptoms (SAPS)]. At the present time, for clinical trials on PD psychosis assessing new treatments, the following are recommended primary outcome scales: NPI (for the cognitively impaired PD population or when a caregiver is required), SAPS, Positive and Negative Syndrome Scale (PANSS), or Brief Psychiatric Rating Scale (BPRS) (for the cognitively intact PD population or when the patient is the sole informant). The CGIS is suggested as a secondary outcome scale to measure change and response to treatment over time.