Pathophysiology of diurnal drooling in Parkinson's disease

Drooling is an incapacitating feature of Parkinson's disease. Better pathophysiological insights are needed to improve treatment. In this study, we tested the hypothesis that the cause of drooling is multifactorial. We examined 15 patients with Parkinson's disease with distinct diurnal saliva loss ("droolers") and 15 patients with Parkinson's disease without drooling complaints ("nondroolers"). We evaluated all factors that could potentially contribute to drooling: swallowing capacity (maximum volume), functional swallowing (assessed with the dysphagia subscale of the Therapy Outcome Measures for rehabilitation specialists), unintentional mouth opening due to hypomimia (Unified Parkinson's Disease Rating Scale item), posture (quantified from sagittal photographs), and nose-breathing ability. We also quantified the frequency of spontaneous swallowing during 45 minutes of quiet sitting, using polygraphy. Droolers had more advanced Parkinson's disease than nondroolers (Unified Parkinson's Disease Rating Scale motor score 31 vs 22; P=.014). Droolers also scored significantly worse on all recorded variables except for nose breathing. Swallowing frequency tended to be higher, possibly to compensate for less efficient swallowing. Logistic regression with adjustment for age and disease severity showed that hypomimia correlated best with drooling. Linear regression with hypomimia as the dependent variable identified disease severity, dysphagia, and male sex as significant explanatory factors. Drooling in Parkinson's disease results from multiple risk factors, with hypomimia being the most prominent. When monitored, patients appear to compensate by increasing their swallowing frequency, much like the increased cadence that is used to compensate for stepping akinesia. These findings can provide a rationale for behavioral approaches to treat drooling.