Hallucinosis in idiopathic Parkinson's disease.

BACKGROUND Hallucinosis is a complication of the treatment of idiopathic Parkinson's disease commonly thought to afflict older, chronically medicated, cognitively impaired patients. However, patients with idiopathic Parkinson's disease of short duration experiencing hallucinosis on relatively low doses of dopaminergic medication have been found. The aim, therefore, was to investigate the homogeneity of a population of patients with idiopathic Parkinson's disease and hallucinosis. METHODS The clinical, demographic, and cognitive correlates of hallucinosis were investigated in a sample of 129 patients with idiopathic Parkinson's disease. RESULTS There were two subgroups of patients with idiopathic Parkinson's disease experiencing hallucinosis. In patients with a disease duration of five years or less, hallucinosis was associated with rapid progression of the motor component of the disease but not cognitive impairment. In patients with idiopathic Parkinson's disease of longer than five years duration, hallucinosis was associated with postural instability, global cognitive impairment, and lack of depressive affect. In all patients with idiopathic Parkinson's disease, hallucinosis was more prevalent when they were treated with a direct acting dopamine receptor agonist. Hallucinosis was not associated with age at onset of idiopathic Parkinson's disease or dosage of dopaminergic medication. CONCLUSION Hallucinosis in idiopathic Parkinson's disease is heterogeneous, falling into two groups. The difference in the pathophysiological basis of hallucinosis in these two groups of patients is discussed.