Language Competence in Parkinson's Disease: A Systematic Review of 20 Years of Research.

PURPOSE: Parkinson's disease (PD) is the second most common neurodegenerative condition worldwide. Although diagnostic criteria heavily rely on the motor component, nonmotor symptoms of PD, including language deficits, are now recognized to emerge several years before its motor manifestations. Assessing the role of language impairment as a nonmotor marker of PD is thus an opportunity to contribute to an effective and timely diagnosis.

METHOD: In this systematic review, we synthesize the state of knowledge on language competence in PD and provide a systematic and comprehensive overview of the issue following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Eligible studies were published from January 2004 to December 2023, and investigated language competence in people having idiopathic PD without dementia.

RESULTS

After reviewing the retrieved records based on our eligibility criteria, we incorporated 45 studies. These studies provided data from a total of 1,037 participants with PD and 1,049 unimpaired individuals. Results show that nondemented people with PD exhibit deficits across multiple language levels. Compromised domains include phonological processing, derivational and inflectional morphology, comprehension of complex syntactic structures, lexical and semantic competence, and pragmatic abilities.

CONCLUSION

Although further research is required to assess the robustness of language impairment as a predictor of PD, results of this systematic review indicate that linguistic data might indeed inform diagnostic criteria and be exploited to complete the clinical picture of PD within the premotor window, reducing diagnostic delay and thus substantially impacting individuals' quality of life.

SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.30625241.