Objective: To examine changes in functional connectivity in patients with Parkinson’s disease (PD) and visual hallucinations (VH) on and off dopaminergic medication.

Background: Symptoms on the psychosis spectrum, including VH, are frequent in PD and increase with the duration of disease. Psychosis is associated with a significantly higher rate of mortality, nursing home placement and caregiver distress. The role of dopaminergic medication in PD psychosis is controversial and has received relatively little research attention. Clinical observations suggest that VH could be linked to medication initiation, levodopa dose and dopamine agonist therapy and improve with dose reduction. However, minor VH occur in drug naïve patients and a levodopa infusion has previously been shown not to induce VH.

Method: Task-based functional magnetic resonance imaging (fMRI) was performed in 15 patients with PD and VH on and off dopaminergic therapy using the Bistable Percept Paradigm (BPP). The BPP is a behavioural task capable of eliciting visual misperceptions and a confirmed surrogate for visual hallucinations. Medication type and levodopa equivalent dose was recorded for all patients.

Results: Differences in functional connectivity in large scale neuronal networks previously implicated in the pathophysiology of visual hallucinations were observed in patients on versus off dopaminergic medication. Differences were observed specifically in the strength of connectivity between primary visual regions and the default mode network.

Conclusion: Dopaminergic therapy is likely a modifier rather than a causal factor in PD psychosis. This study contributes to understanding of its modulation of neural mechanisms including visual processing and attention underlying VH in PD.

References: 1. Ffytche DH, Creese B, Politis M, Chaudhuri KR, Weintraub D, Ballard C et al. The psychosis spectrum in Parkinson disease. Nat Rev Neurol 2017;13(2):81-95. 2. Shine JM, Muller AJ, O’Callaghan C, Hornberger M, Halliday GM, Lewis SJG. Abnormal connectivity between the default mode and the visual system underlies the manifestation of visual hallucinations in Parkinson’s disease: a task-based fMRI study. NPJ Parkinsons Dis 2015;1:1-8. 3. Lenka A, Herath P, Christopher R, Pal K. Psychosis in Parkinson’s disease: From the soft signs to the hard science. J Neurol Sci 2017;379:169-176.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-effect-of-dopaminergic-therapy-on-functional-connectivity-in-patients-with-parkinsons-disease-and-visual-hallucinations/