Objective: This study aimed to examine whether the language impairment is presented in isolated rapid eye movement sleep behavior disorder (iRBD) and early-stage Parkinson’s disease (PD) with or without the presence of mild cognitive impairment (MCI).

Background: Patients with synucleinopathies frequently display language abnormalities. However, whether patients with iRBD and de-novo PD have prodromal language impairment remains unknown.

Method: We investigated 139 Czech male native participants of comparable age and education level, including 40 iRBD without MCI (iRBD-nMCI), 14 iRBD with MCI (iRBD-MCI), 40 PD without MCI (PD-nMCI), and 15 PD with MCI (PD-MCI), compared to 30 healthy controls. Spontaneous discourse and story tale narrative were transcribed and linguistically annotated. A quantitative analysis was performed computing four linguistic features. Human annotations were compared to fully-automated annotations.

Results: Compared to controls, both iRBD-nMCI and iRBD-MCI groups showed poorer content density (p < 0.05), reflecting the reduction of content words and modifiers. The presence of MCI was associated with poorer lexical richness. Less occurrence of unique words was found in both PD-MCI (p < 0.001) and iRBD-MCI (p < 0.05) subgroups, as well as a higher number of n-grams repetitions was observed in both PD-MCI (p < 0.001) and iRBD-MCI (p < 0.01) subgroups. The spontaneous discourse task demonstrated language impairment in iRBD-nMCI with an area under the curve of 0.73, while the story tale narrative task better reflected the presence of MCI, discriminating both PD-MCI and iRBD-MCI subgroups from controls with an area under the curve of up to 0.88. A strong correlation between manually and automatically computed results was achieved (r = 0.84-0.97, p < 0.001).

Conclusion: We identified language abnormalities that are sensitive to the iRBD phenotype as well as the presence of MCI. The results indicate that linguistic analysis could be a promising method to detect subtle cognitive decline due to prodromal neurodegeneration in iRBD. Future research is warranted to elaborate on linguistic features for the best prediction of phenoconversion from iRBD to manifest parkinsonism or dementia. This study was supported by the Czech Ministry of Health (grants no. NV19-04-00120 and NU20-08-00445).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/language-impairment-in-isolated-rapid-eye-movement-sleep-behavior-disorder-and-de-novo-parkinsons-disease/