[A unique hallucination in the context of Parkinson's disease: reduplication or misidentification?]

We discuss a case involving a 75-year-old man with Parkinson’s disease (PD) who experienced a psychotic duplication phenomenon. This resembled Capgras syndrome, a misidentification delusion characterized by the false belief that a familiar person has been replaced by a double. However, our patient did not exhibit a delusion but rather a hallucination in which he simultaneously perceived his partner in two locations. He consistently engaged with the hallucinatory experience of his partner, whom he saw duplicated at the table, without awareness of the inaccuracy of this perception. Therefore, this may be better classified as a psychotic duplication experience, or reduplicative paramnesia. A similar phenomenon has been described twice previously in Lewy body dementia, where the distinction between delusion and hallucination was also unclear. Throughout the course of Parkinson’s disease, diverse neuropsychiatric symptoms can occur, including variants of reduplication and misidentification. Distinguishing these phenomena in our case was challenging, and we discuss the underlying mechanisms.