Validation of the Psychosis and Hallucinations Questionnaire in Non-demented Patients with Parkinson's Disease.

People diagnosed with Parkinson's disease (PD) frequently experience visual and non-visual hallucinations often with comorbid psychosis, however, there is currently no gold standard tool for accurately assessing these symptoms. To address this problem, we designed a novel questionnaire to evaluate the presence of hallucinatory and psychotic symptoms in PD, as well as related symptoms, such as attentional dysfunction and sleep disturbance. We administered the 20-item Psychosis and Hallucinations Questionnaire (PsycH-Q) and three common questionnaire measures in a large cohort of 197 patients with idiopathic PD via a postal survey. We established concurrent validity, convergent validity, and internal consistency of the questionnaire and then assessed test-retest reliability in a subcohort of 44 patients. PsycH-Q was found to be a valid instrument when analogous items were compared across three other existing tools (Spearman's rho range: 0.34-0.64; P < 0.01). PsycH-Q demonstrated a strong relationship between self-reported hallucinations and psychosis and symptoms of the broader hallucinatory phenotype (Kendall's tau = 0.41; P < 0.01; positive predictive value = 0.97). PsycH-Q also displayed a high level of internal consistency (Cronbach's alpha = 0.900; range, 0.696-0.923) and reproducibility (intraclass correlation coefficient = 0.928). PsycH-Q is a simple, valid, self-completed instrument that reliably identifies hallucinations and psychosis in PD and has the ability to characterize related patterns of attentional and sleep impairments. As such, PsycH-Q is a highly valuable tool for use in both clinical and research settings.