This study reports that bilingual early-stage idiopathic Parkinson's patients exhibit microstructural language deficits (lower MLU-M, more morphological errors and verbal fragmentation), pragmatic changes (fewer enrichment expressions, more exclamations), and altered prosody, with bilingualism…

Offers a noninvasive discourse-level behavioral biomarker for early/subclinical PD detection and patient stratification that could inform clinical assessments and outcome measures in trials, though it does not provide molecular mechanisms or direct therapeutic targets.

PURPOSE: This study examined how bilingualism influences early linguistic and pragmatic alterations in idiopathic Parkinson's disease (IPD), integrating group-based and factorial analyses to identify early communicative markers. METHOD: Sixty-five participants (13 bilingual IPD, 14 monolingual IPD, 14 bilingual healthy, 24 monolingual healthy) produced Turkish narratives based on Frog, Where Are You? Group comparisons (Kruskal-Wallis H and Mann-Whitney U tests) were performed across four groups for microstructural indices (mean length of utterance in morphemes [MLU-M], type-token ratio [TTR], morphological errors, verbal fragmentations) and pragmatic markers (enrichment, exclamation, uncertainty, metaphor, emotional terms). Supplementary 2 × 2 factorial analyses (disease: IPD vs. healthy; bilingualism: bilingual vs. monolingual) were conducted to examine main and interaction effects, with acoustic parameters (fundamental frequency [F0] and intensity ranges) included for prosodic evaluation. RESULTS: Group comparisons revealed that bilingual IPD speakers exhibited the lowest MLU-M (p = .012), highest morphological error (p = .036), and greatest verbal fragmentation (p < .001). Pragmatically, they produced fewer enrichment expressions (p = .041) but more exclamations than monolingual IPD participants (p < .001). Acoustic analysis showed reduced but still broader F0 and intensity ranges in bilingual IPD speakers relative to monolingual IPD speakers (p = .012, p = .047). The 2 × 2 factorial analysis confirmed significant main effects of disease on MLU-M and TTR (p < .05) and Disease × Bilingualism interactions for morphological errors and enrichment (p < .05), demonstrating that bilingualism amplified morphosyntactic instability but mitigated prosodic flattening. CONCLUSIONS: Early-stage IPD involves concurrent microstructural and pragmatic decline, with bilingualism exerting both protective and burdening effects. Crucially, the reduction of enrichment expressions (p < .05) emerged as an early and sensitive indicator of pragmatic deterioration in bilingual Parkinson's disease, linking executive-control demands with sociopragmatic incompleteness. Discourse-level analyses combining group-based and factorial approaches thus provide a refined framework for identifying subclinical linguistic-pragmatic changes beyond conventional motor or lexical measures. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.31999344.