Clinical and autonomic correlates of chronic Sialorrhea in Parkinson's disease: a questionnaire-based study with cluster analysis of autonomic and dysphagia burden

Introduction: Chronic sialorrhea is common in Parkinson's disease (PD), but its clinical correlates and patient awareness of treatment options remain unclear. We examined factors associated with drooling, focusing on autonomic dysfunction and dysphagia, and assessed perceptions of botulinum toxin therapy. Methods: We conducted a questionnaire-based study of consecutive PD outpatients at Keio University Hospital from October to December 2025. Drooling was defined using MDS-UPDRS Part II item 2. Autonomic symptoms were assessed with SCOPA-AUT and swallowing with the Swallowing Disturbances Questionnaire (SDQ). Clinical variables and 123 I-metaiodobenzylguanidine myocardial scintigraphy indices were extracted from medical records. Multivariable logistic regression identified factors independently associated with drooling. K-means clustering (k = 3) was also performed among droolers using standardized SCOPA-AUT and SDQ scores. Results: Among 208 patients, 116 (55.8%) were classified as droolers. Droolers were more often male and had longer disease and treatment duration, higher Hoehn and Yahr stage, higher levodopa equivalent daily dose, higher SDQ scores, more severe autonomic symptoms, and lower MIBG heart-to-mediastinum ratios. In multivariable analysis, higher SCOPA-AUT and SDQ scores remained independently associated with drooling. Only 34.5% of droolers perceived drooling as problematic, 14.7% were aware of botulinum toxin therapy, and 21.6% were willing to receive injections. Clustering identified three phenotypes: low autonomic/low dysphagia, high autonomic/high dysphagia, and high autonomic/low dysphagia. Conclusion: Chronic sialorrhea in PD is associated with dysphagia burden and broader autonomic dysfunction, suggesting heterogeneous mechanisms. Limited awareness highlights the need for systematic screening and patient education.