Hallucinations and psychosis in Parkinson's disease.

Although Parkinson's disease (PD) is considered mainly a movement disorder, robust information accumulated during the last 30 years has shown that about 30% of PD patients may also suffer from psychosis, which deeply affects their quality of life and eventually brings them to permanent hospitalization in nursing homes. PD psychosis (PDPsy) mainly occurs after 10 or more years of treatment. The main features of PDPsy include recurrent and continuous hallucinations and delusions for at least 1 month. In addition, a recent consensus of the National Institute of Neurological Disorders and Stroke and National Institute of Mental Health Working Group also included illusions and a false sense of presence as "minor symptoms" supporting the diagnosis. In addition, accumulated clinical data have shown that "minor symptoms" and benign hallucinations also imply a bad prognosis with time. In the diagnostic criteria for PDPsy, it is considered that patients suffer from PD for at least more than 1 year before psychosis develops. If this is not the case, there is an unsolved problem of an overlapping diagnosis with Dementia with Lewy Bodies. Most clinicians consider that the main cause of psychosis is chronic exposure to dopaminergic medication. However, from an operational point of view there remain difficulties in defining a specific time of exposure and dose of treatment and the occurrence of PDPsy. Specific rating scales have been developed for the evaluation of PDPsy, such as the Parkinson Psychosis Rating Scale. The Scale for the Assessment of Positive Symptoms usually applied in schizophrenic patients has also proved useful for scoring psychotic symptomatology in PD. Clozapine in low doses has been proven to be the most effective antipsychotic medication for PDPsy. However, its use may cause neutropenia. Therefore, new atypical antipsychotic drugs with serotonin 5-HT2A receptor inverse agonist properties have been developed. Recently, pimavanserin--a 5-HT2A inverse agonist--has been studied. We hope that soon we will have the possibility to include new agents for the management of PDPsy.