Hallucinations and sleep disturbances in Parkinson's disease.

Visual hallucinations (VHs) occur frequently in Parkinson's disease (PD). VHs occur more frequently in elderly patients with longer duration of illness, cognitive impairment, and sleep disturbances. The relationship between the use of antiparkinsonian drugs and VHs is complicated, but most drugs used to treat parkinsonian motor symptoms induce VHs and psychosis in some PD patients. The "continuum hypothesis" proposing that medication-induced psychiatric symptoms in PD begin with drug-induced sleep disturbances, followed by vivid dreams, with progression to hallucinatory and delusional experiences has been challenged. In some patients, VHs may represent intrusion of REM sleep-related imagery into wakefulness. Improving REM sleep abnormalities in PD (e.g., stimulants, anticholinesterase inhibitors) is one strategy now being tested to improve VHs in PD.