Pareidolias and cognition in isolated REM sleep behavior disorder

Background: Though visual illusions and hallucinations are common in dementia with Lewy bodies (DLB) and Parkinson's disease (PD), they are not typically observed clinically in prodromal stages, including isolated REM sleep behavior disorder (iRBD). False-noise errors on the pareidolia test (seeing faces when none are present) may be an effective measure of susceptibility to future hallucinations in iRBD. Methods: One hundred patients with iRBD underwent the 20-image pareidolia test. Clinical markers were assessed and a neuropsychological battery was administered. An exploratory analysis on the impact of pareidolic errors on phenoconversion was also performed. Results: In our cohort, 17 patients (17%) made false-noise pareidolic errors. These patients had significantly lower total Montreal Cognitive Assesment (MoCA) scores (26.7 +/- 2.3 vs. 24.4 +/- 2.6, B = -1.88, 95% CI: [-3.17, -0.59]), with lower subcomponent MoCA scores on memory and visuospatial-executive sections. Pareidolic errors were also associated with lower visuospatial, attention/executive, and memory scores on the neuropsychological tests. Furthermore, after 1.6 years follow-up, 3/16 (19%) patients making pareidolic errors had phenoconverted at time of publication compared to 6/71 (8%) patients who did not make errors. Conclusion: Pareidolic errors in patients with iRBD are associated with poorer overall cognition and may indicate higher risk of DLB.