Psychotic symptoms such as hallucinations and delusions are common in patients with Parkinson's disease (PD). The estimated prevalence of hallucinations ranges from ~10% to 48%, and the prevalence of delusions ranges from 3% to 80%(ref 1–9). The various of the prevalence depends of the diagnostic criteria used. The etiologies of these symptoms are multiple and treatments are different. Through a clinical observation of a patient treated for a Parkinson disease (PD) and who develop two years ago a behavior disorder, irritability, visual hallucination and illusion, we suggest discussing the etiologies and the therapeutic difficulties of this disorder.

Y.N., a 64 year-old man, with family history of dementia, and personal history of diabetes and tuberculosis. He is followed for Parkinson's disease since the age of 57 years. He received Trihexyphenidyle (5 mg per day), Piribedil (200mg per day) and levodopa (500mg per day) with a progressive increase and excessive consumption of levodopa (more than 1000mg per day). Since the age of 62 years old, he presented with elaborated and invalidating auditory hallucinations with ideas of persecution and prejudice. The neuropsychological evaluation showed no other signs of dementia (MMSE=30/30). The diagnosis of dopaminergic psychosis was established. Levodopa was decreased; Trihexyphenidyle and Piribedil were discontinued with a notable improvement of hallucinations.

The psychotic symptoms in PD should be searched, such as systemic illness and other psycho-active medications. If none are identified or can be eliminated, the PD medications should be reduced to the lowest levels that allow tolerable motor function. Once this level has been reached we can use either acetylcholinesterase inhibitors or typical anti-psychotics