Specificity of non-motor symptoms of Parkinson’s disease : A systematic review and meta-analysis

UNSPECIFIED (2026) Specificity of non-motor symptoms of Parkinson’s disease : A systematic review and meta-analysis. Sage Open Chronic Disease, 17. ISSN 2978-1558

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Abstract

Background: Middle-aged and older adults (>55 years old) have a high risk of developing Parkinson’s disease (PD); however, many non-motor symptoms (NMSs) indicative of PD are also common in middle-aged and older adults without a neurological disease diagnosis. Objective: To identify symptoms specific to PD in comparison to controls without a neurological disease diagnosis. Design: This is a systematic review and meta-analysis. Data source and methods: We performed a meta-analysis, using Embase, SciSearch, MEDLINE, and BIOSIS from January 1, 2001, until April 1, 2025. We included observational studies reporting the prevalence of NMSs using the non-motor symptom questionnaire or non-motor symptom scale in the PD population versus controls. Using a random effects model, we generated a pooled estimate for the prevalence risk ratio (RR) for each symptom. Results: The meta-analyses included 15 studies, involving 7393 PD patients and 2742 controls. It showed 28 out of 30 NMSs were more common in the PD population, with excessive drooling (RR = 7.30 (95% confidence interval; CI 5.05–10.57)), visual hallucinations (RR = 6.48 (95% CI 3.61–11.64)) and taste/smell issues (RR = 4.67 (95% CI 3.07–7.10)) being the most specific symptoms (having the largest RRs). Conclusion: Planning screening campaigns to identify PD among middle-aged and older adults is difficult, due to the high numbers that are needed to screen using tools that are not specific enough. We showed that excessive drooling and taste/smell issues are highly specific NMSs of PD, as they have high RRs. More research is needed to assess their usefulness to be included as an enrichment factor in screening campaigns for PD patients in a middle-aged and older adult population.