Lexico‐Semantic and Morphosyntactic Skills in Individuals With Parkinson's Disease: A Scoping Review

Abstract

ABSTRACT Purpose This scoping review examines lexico‐semantic and morphosyntactic skills in English‐speaking individuals with Parkinson's disease (PD) using behavioral and neuroimaging data to inform clinical assessment and intervention. Method Following PRISMA‐ScR guidelines, observational case‐control studies published between 2004 and 2024 were retrieved from PubMed, PsycINFO, Web of Science, Scopus and ERIC. Thirty‐nine studies met inclusion criteria. Methodological quality was evaluated using the Joanna Briggs Institute Checklist for Case‐Control Studies. Results Lexico‐semantic impairments in PD are characterized by deficits in semantic fluency, action‐verb retrieval, and figurative‐language processing, particularly under higher cognitive load. Individuals with PD show reduced efficiency in lexical access, difficulty shifting between semantic categories, and weaker inhibition of competing meanings. Morphosyntactic studies similarly report slower processing and lower accuracy for syntactically complex sentences. Conclusion Linguistic impairments in PD are best understood as a dynamic interaction between linguistic demands and domain‐general cognitive resources, emerging most clearly under conditions of increased cognitive load. This pattern positions language as a sensitive indicator of broader cognitive vulnerability within the communication profile of PD, with direct implications for assessment and clinical practice. WHAT THIS PAPER ADDS What is already known on the subject Language impairments are a well‐recognized non‐motor feature of PD and can significantly affect communication and quality of life. Previous studies have reported lexico‐semantic and morphosyntactic difficulties in PD, but findings are scattered across heterogeneous tasks and study designs, with no synthesis examining these domains together. What this study adds to the existing knowledge This scoping review synthesizes evidence from behavioral and neuroimaging studies and shows that language difficulties in PD are most consistently observed under conditions of increased cognitive or processing demand, particularly in high‐load contexts. Lexico‐semantic impairments emerge reliably in such high‐load contexts, while morphosyntactic difficulties appear to reflect vulnerability to processing demands rather than a generalized grammatical deficit. The review also demonstrates that methodological variability, such as cognitive screening practices, influences how language abilities are characterized across studies. What are the potential or clinical implications of this work? Language impairments affecting lexico‐semantic and morphosyntactic processing constitute a meaningful component of the communication profile in PD and should be considered alongside speech and voice symptoms in clinical assessment. Incorporating cognitive–linguistic evaluation may support a more comprehensive understanding of communication difficulties in individuals with PD.