Parkinson's disease psychosis encompasses a range of symptoms, including minor phenomena, frank hallucinations, and delusions. Minor phenomena include passage hallucinations (fleeting sense of a person, animal or object passing in the periphery), presence hallucinations (feeling of nearby presence), and illusions (misrepresentation of external stimuli). Some forms of PD psychosis may be progressive. The primary objective of this study is to:

1) To determine the cumulative probability of developing hallucinations or delusions over time in individuals with PD minor phenomena followed for 36 months.

Inclusion Criteria:

• Parkinson's disease (as determined by Movement Disorders Society diagnostic criteria for clinically probable Parkinson's disease)
• Parkinson's disease minor phenomena
• ≥30 years of age
• Proficient in English
• Willing and able to provide informed consent

Exclusion Criteria:

• Any current or prior history of formed hallucinations or delusions
• Current or prior treatment with an antipsychotic medication (regardless of indication)
• Diagnosis of mania with psychotic features, bipolar or related disorder, depression with psychotic features, or a psychotic disorder
• Unable or unwilling to complete study activities
• Any medical or psychiatric comorbidity that, in the opinion of the investigator, would compromise study participation

Participants must meet criteria for clinically probable PD according to the MDS clinical diagnostic criteria for PD. Notably, in these new criteria, PD and dementia with Lewy bodies are recognized as most likely existing on a continuous spectrum and dementia is not an exclusion criterion for PD.