Sialorrhea in Parkinson's disease: prevalence, impact and management strategies

Saliva plays an important part in oral health maintenance, mastication, deglutition and the start of the digestive process. It supports clear speech. Alterations to the composition and flow of saliva through hyper- or hyposecretion or anterior loss through the lips thus have potentially significant consequences. This article reviews the metrics, possible age and gender differences and diurnal variability of flow in healthy individuals. It then focuses on the ways in which this is altered in Parkinson's disease (PD) and the possible mechanisms for why people with PD drool. It reviews procedures for clinical assessment and management. Many studies report drooling prevalence >50% of people with PD, though in the early stages the impact may not yet be great. In PD, saliva flow is normal or even decreased compared to people without PD. Motorically sialorrhea arises from an interaction between oro-facial rigidity, lingual bradykinesia and aspects of oro-pharyngeal dysphagia. Postural, cognitive, attentional and pharmacological factors may also contribute. Objective evaluation of sialorrhea looks at the rate and variability of flow (milliliters or milligrams per unit time; swallow intervals; consistency). Since objective measures seldom reflect patient-reported lived experience, assessment includes rating scales that capture subjective concerns. Because altered salivary function impacts on (peri)oral health, assessment and monitoring of this is strongly advocated. Methods in each of these assessment domains are introduced. Clinical guidelines recommend behavioral interventions in the first instance, with pharmacological treatments, including botulinum injection, as follow-up possibilities. Surgical procedures are reserved for severe or intractable cases. High-quality evidence for the efficacy of behavioral interventions is lacking. Drug therapy efficacy is also under-studied, apart from botulinum toxin management. Few studies have examined surgical interventions in PD, though principles are well established from other populations. Strands of enquiry for improving our knowledge of behavioral interventions are suggested.