Capgras syndrome in Parkinson's disease: two new cases and literature review.

The Capgras syndrome (CS) is a rare psychiatric disorder. CS is classified as a delusional misidentification syndrome. Initially, CS was described in paranoid schizophrenia and schizoaffective disorders. CS has also been reported in neurodegenerative diseases such as Alzheimer's disease and Lewy body dementia. To date, there are very few descriptions of the occurrence of CS in idiopathic Parkinson's disease (PD), with or without dementia. Considering the recent observation of two new cases in PD patients, a systematic overview of the literature published between 1976 and 2016 reporting CS in PD was conducted. The purpose of this article is to examine the phenomenon in people with PD with and without dementia, the psychopathologic context in which it happened, the role played by the dopaminergic medications and to define useful therapeutic strategies. Our CS cases occurred in two elderly patients with advanced PD and cognitive impairment, respectively, after an acute stressor event and after an increase of the total daily dose of levodopa. In light of our observations and the cases reported in the literature, we argue that CS is an acute or subacute psychotic disorder occurring mostly in PD with dementia. Besides, the increase in brain dopamine levels induced by acute stressful events and/or dopamine-enhancing medications should be considered as a possible causal mechanism of CS in patients with advanced stages of PD and cognitive decline.