Linguistic Abnormalities in Isolated Rapid Eye Movement Sleep Behavior Disorder

Abstract

Background: Patients with synucleinopathies frequently display language abnormalities. However, whether patients with isolated rapid eye movement sleep behavior disorder (iRBD) have prodromal language impairment remains unknown. Objectives: We examined whether the linguistic abnormalities in iRBD can serve as potential biomarkers for conversion to synucleinopathy, including the possible effect of mild cognitive impairment (MCI), speaking task, and automation of analysis procedure. Methods: We enrolled 139 Czech native participants, including 40 iRBD without MCI and 14 iRBD with MCI compared to 40 PD without MCI, 15 PD with MCI, and 30 healthy controls. Spontaneous discourse and story tale narrative were transcribed and linguistically annotated. A quantitative analysis was performed computing 3 linguistic features. Human annotations were compared to fully-automated annotations. Results: Compared to controls, iRBD patients showed poorer content density, reflecting the reduction of content words and modifiers. Both PD and iRBD subgroups with MCI manifested less occurrence of unique words and a higher number of n-grams repetitions, indicating poorer lexical richness. The spontaneous discourse task demonstrated language impairment in iRBD without MCI with an area under the curve of 0.72, while the story tale narrative task better reflected the presence of MCI, discriminating both PD and iRBD subgroups with MCI from controls with an area under the curve of up to 0.81. A strong correlation between manually and automatically computed results was achieved. Conclusions: Linguistic features might provide a reliable automated method for detecting cognitive decline due to prodromal neurodegeneration in subjects with iRBD, providing critical outcomes for future therapeutic trials.