[Psychotic symptoms in Parkinson's disease]

About one third of patients with Parkinson's disease (PD) experience hallucinations, mostly of a complex visual type, less often auditory or tactile. Minor hallucinatory phenomena, including sense of presence, passage hallucinations and visual illusions are frequent. Hallucinations primarily occur in a context of clear sensorium in patients with longstanding PD. They are more frequent in the evening or during the night. Insight in the hallucinatory nature of the phenomenon may be retained, partial, fluctuating, or abolished. An altered insight is common when cognitive impairment is present, and may be associated with delusions and (or) delusional misidentifications. Pharmacological factors such as dopaminergic treatment clearly trigger or increase the occurence of hallucinations in PD. However, in the recent years, emphasis has been made on disease-related factors including cognitive impairment, diurnal somnolence, visual disorders (either contrast and color discrimination impairment due to PD, or coincident ocular disorders), long duration of PD, late onset, severe axial impairment and autonomic dysfunction. The pathophysiology of hallucinations of PD is poorly understood but is likely to be multifactorial. The first steps of the treatment consist in giving information and reassurance to the patient and his/her caregiver, re-evaluating the antiparkinsonian treatment and associated medications, and evaluating the patient for mood disorder, visual impairment, and cognitive impairment. Cholinesterase inhibitors, when prescribed for associated cognitive impairment, may be beneficial on hallucinations. In the more severe forms, clozapine has been proved to be safe and effective.