Objective: To investigate the prevalence, incidence, risk factors, and concomitants of Parkinson disease (PD)-associated psychosis (PDP) in a population-based prevalent cohort.
Design: Prospective longitudinal cohort study.
Setting: Community-based study in southwestern Norway.
Participants: Two hundred thirty community-based PD patients were followed up prospectively for 12 years. Reassessments were conducted at 4 and 8 years and then annually.
Main outcome measures: Severity of PDP was measured by the Unified Parkinson Disease Rating Scale thought disorder (UPDRS-TD) item. Patients with a UPDRS-TD score of 2 or more or those taking antipsychotic drugs owing to psychotic symptoms were categorized at each visit as having PDP. Generalized estimating equations were applied to investigate baseline risk factors for incident PDP and clinical and demographic concomitants of PDP during 12 years.
Results: By study's end, 137 patients (60%) had developed hallucinations or delusions. The incidence rate of PDP was 79.7 per 1000 person-years. Higher age at onset, higher baseline levodopa-equivalent doses, probable rapid eye movement (REM) sleep behavior disorder at baseline, and follow-up time were independent risk factors of incident PDP. Significant concomitant features of patients with PDP during the 12-year study period were low activities of daily living function (UPDRS II), dementia, high levodopa-equivalent dose, and probable REM sleep behavior disorder.
Conclusions: Psychotic symptoms affect most patients with PD, with increased risk in those with higher age at onset, need for high doses of dopaminergic drugs, and probable REM sleep behavior disorder. This risk factor pattern and the observed associations with increased disability and dementia place PDP within a symptom complex signaling a malignant disease course.