Delusions in Parkinson's Disease: A Systematic Review of Published Cases.

Delusions in Parkinson's disease (PD) are thought to be associated with disease progression and cognitive impairment. However, this symptom description is not consistent in the literature and there is a suggestion that different subgroups of psychotic patients occur in PD, which we aimed to clarify. Case reports were identified through a systematic search of databases (PUBMED, EMBASE, PsychInfo). Cases with isolated delusions were compared to those with both delusions and hallucinations. We identified 184 cases of delusions in PD. Delusions were primarily paranoid in nature (83%) and isolated in 50%. Those with isolated delusions had an earlier onset of PD (46 years vs 55 years), higher rates of impulse control disorders (40.2 vs 10.3%), dopamine dysregulation (29.9 vs 11.3%) and lower rates of cognitive impairment (8.0 vs 26.8%). There is unexpected heterogeneity amongst cases of delusional psychosis, that cannot adequately be explained by existing models of PD psychosis.