Objective: To investigate whether hypnagogic/hypnopompic experiences are clinically misinterpreted as hallucinations in Parkinson’s disease.

Background: In Lewy body disorders, the progression of the disease can produce psychotic symptoms, ranging from minor hallucinations to well-structured visual hallucinations and delusions. However, the psychotic nature of these symptoms is often not evident, due to the semantic and perceptual ambiguity between hallucinations (occurring by definition in the fully awake state) and hypnagogic/hypnopompic experiences (occurring in the transition to and from sleeping states) (Foffani, 2024).

Method: A cohort of 58 well-studied patients with Parkinson’s disease (21 females, 70.1±7.5 years old, 7.5±6.2 years of disease duration, 26.6±10.4 MDS-UPDRS-III OFF medication) was scored for hallucinations and psychosis using the MDS-UPDRS-Part I (item 1.2). The scoring was first performed following the standard instructions (Y), and then repeated twice explicitly focusing on experiences occurring either “while sleeping, falling asleep or awakening” (Xhynp, i.e. hypnagogic/hypnopompic experiences) or “being fully awake in the day” (Xhall, i.e. hallucinations). Frequentist and Bayesian correlations, partial correlations and multiple regression (Y≈a1*Xhall+a2*Xhypn) were then employed to assess whether the standard scoring was actually specific for hallucinations (null hypothesis, a2=0) or was contaminated by hypnagogic/hypnopompic experiences (alternative hypothesis, a2≠0).

Results: Both Xhall and Xhypn correlated with Y with extreme Bayesian evidence (Pearson’s r>0.60, BF+0>6*10^4; Kendall’s Tau B>0.50, BF+0>1*10^6). The evidence of a correlation between Xhypn and Y remained extreme even after conditioning on Xhall (Pearson’s r=0.48; Kendall’s Tau B=0.34). When Xhall and Xhypn were considered jointly, we confirmed with extreme evidence that Xhynp contributed to the standard scoring (a2≠0; BFincl=303.7).

Conclusion: Our results show that hypnagogic/hypnopompic hallucinations may be misinterpreted as hallucinations when using standard clinical scales intended to rate hallucinations and psychosis in Parkinson’s disease. Updated scales, metacognitive strategies and/or polysomnographic confirmation should be developed, validated and employed to differentiate truly psychotic hallucinations from relatively normal hypnagogic/hypnopompic experiences (Foffani, 2024).

References: Foffani G. To be or not to be hallucinating: Implications of hypnagogic/hypnopompic experiences and lucid dreaming for brain disorders. PNAS Nexus. 2023 19;3(1):pgad442.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/misinterpretation-of-hypnagogic-hypnopompic-experiences-as-hallucinations-in-parkinsons-disease/