Psychoses in Parkinson's Disease

Psychotic symptoms occur in up to 40% of patients with Parkinson's disease (PD) and other degenerative parkinsonian disorders, usually but not exclusively in the context of their pharmacologic treatment. We describe the following six psychotic syndromes in PD based on existing literature: (1) hallucinations with preserved insight; (2) medication-induced psychotic disorders (in clear consciousness); (3) delirium; (4) schizophrenia-like psychotic disorders (in clear consciousness and in the absence of medication treatment); (5) schizophrenia with subsequent development of PD; and (6) other psychotic disorders. Psychosis in PD has been noted to be a marker for illness deterioration. Psychotic symptoms can profoundly affect the quality of life for PD patients and their families and may increase the economic burden of this illness. Various approaches have been used to treat psychotic symptoms in PD. We critically review this literature, which is limited, but includes studies indicating promise for "atypical" antipsychotics in these patients. Further elucidation of the phenomenology, course, pathophysiology, and treatment of the different psychotic disorders in PD is urgently needed.