However, the authors found a close association between hallucinations and altered dream phenomena but not sleep fragmentation. It should be emphasized that sleep disturbances are frequent in the course of Parkinson's disease, even in the absence of hallucinations, and data from clinical studies do not allow one to conclude that sleep disturbances as a whole and hallucinations are on a continuum and share a common pathophysiological mechanism.
In this regard, polysomnographic studies comparing Parkinson's disease patients with and without hallucinations could be valuable. We are aware of only one such study, which included five patients in each group Comella et al.
The Ophthalmologist’s Role
Compared with non-hallucinators, patients with hallucinations had a lower sleep efficiency, a reduced total REM rapid eye movement sleep time and a reduced REM percentage. These findings suggest a link between REM sleep abnormalities and the development of hallucinations during the course of Parkinson's disease. An association between a disturbance of the sleep—wake cycle and hallucinations occurs in other conditions, such as narcolepsy and peduncular hallucinosis.
Lhermitte stressed similarities between dreams and peduncular hallucinosis and suggested that, in the latter condition, hallucinations might arise from a dysfunction of sleep—wake mechanisms secondary to the peduncular lesion Lhermitte, Accordingly, lesions in Parkinson's disease might involve brainstem structures controlling sleep, especially those generating REM sleep Manford and Andermann, Previous studies showed that Parkinson's disease patients with hallucinations were more disabled than non-hallucinators Sanchez-Ramos et al.
We also found that motor status was more severely affected in hallucinators than in non-hallucinators but did not emerge as a factor predictive of visual hallucinations in multivariate analysis. This could be due to the correlation of motor impairment with the duration of the disease, the latter remaining a predictive factor in the multivariate analysis. We found that patients with formed visual hallucinations had a higher CES-D score than patients without hallucinations, but this score was not a predictive factor in the multivariate analysis.