Psychotic symptoms complicate the clinical differentiation of Parkinson's disease with major depressive disorder from dementia with Lewy bodies.

Dementia with Lewy bodies (DLB) is diagnosed clinically according to the diagnostic criteria in the Third Report of the DLB Consortium. However, psychotic symptoms, such as visual hallucinations, delusions, and stupor, may complicate the clinical diagnosis of DLB. The present study reports on a patient with Parkinson's disease that was difficult to distinguish from DLB because of the presence of various psychotic symptoms. In making a diagnosis of DLB, it is important to assess essential psychiatric features and to observe patients for any changes in these features.