Objective: To systemically evaluate visual hallucinations and illusions in patients across the LBD spectrum and to discover the underlying neural mechanism behind these visual symptoms.

Background: Recurrent visual hallucinations are core clinical features of dementia with Lewy bodies (DLB) which help differentiate from other degenerative disorders, and are also common in Parkinson’s disease (PD) patients. However, little is known whether these features can also be detected in isolated REM sleep behavior disorder (iRBD), a prodromal stage of Lewy body disease (LBD).

Method: We prospectively assessed visual symptoms in our cohort of iRBD, PD and DLB using the Korean Questionnaire for Visual Symptoms and Hallucination in Parkinson’s disease (K-QVH), a self-reported 20-item questionnaire for the evaluation of general visual dysfunction (part 1) and illusions or hallucinations (part 2), and the noise pareidolia test. Clinical symptoms were also evaluated with the MDS-UPDRS and a predefined neuropsychological test. All participants underwent brain MRI and 18 F-fluorodeoxyglucose PET. Whole brain voxel-based morphometry and volumes of the basal forebrain cholinergic nucleus were analyzed. Brain metabolic activity was analyzed in correlation with K-QVH and noise pareidolia test scores.

Results: A total of 102 subjects (39 iRBD, 42 PD, and 21 DLB) were included in this study. Visual hallucinations correlated with autonomic dysfunction in all groups, with UPDRS scores in PD patients, and with visuospatial dysfunction in DLB patients. Basal forebrain atrophy was seen in PD and DLB patients with visual hallucinations, but not with pareidolias. Pareidolias were associated with decreased frontal volume in the RBD group, and with decreased volume in the occipito-temporal regions in the whole LBD group. Bilateral occipito-temporal hypometabolism was associated with both pareidolias and hallucinations, while hypometabolism in the frontal area correlated with pareidolias in patients across the LBD spectrum.

Conclusion: Visual perceptual abnormalities can be detected by a systematic evaluation tool in prodromal stage of LBD. While both visual symptoms share a similar metabolic pattern encompassing hypometabolism in the posterior brain regions, cholinergic degeneration seems to be responsible in part for the generation of hallucinations, and frontal hypometabolism is more pronounced in pareidolias.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/visual-hallucinations-and-pareidolias-across-the-lewy-body-disease-spectrum/