Behavioural interventions for swallowing in subjects with Parkinson's disease: A mixed methods systematic review

Dysphagia is prevalent in subjects with Parkinson's disease (PD). Swallowing intervention to improve or maintain swallowing function is of major importance as dysphagia may considerably impact physical and psycho-social health.

A mixed methods systematic review was conducted to summarize and appraise literature reporting (1) effects of behavioural interventions for swallowing in individuals with PD; and (2) participants' perspectives of swallowing interventions.

Electronic databases were searched systematically in July 2020 for articles published between 2014 and 2020. In addition, studies published between 2000 and 2014 were identified non-systematically through previous reviews. Peer-reviewed quantitative and qualitative research in English or German documenting behavioural interventions for swallowing in individuals with a diagnosis of PD was eligible for inclusion. Participants at all disease stages were included. Behavioural interventions included rehabilitative and compensatory strategies. Studies reporting swallowing outcomes with and without a comparative group were included. For each study, the National Health and Medical Research Council level of evidence was defined. Included studies were critically appraised using the Standard Quality Assessment Criteria for Evaluating Primary Research Papers from a Variety of Fields. An integrated synthesis was performed after separate analysis of effect data and data reflecting participants' experiences. This review was conducted based on published JBI methodology and the guideline from the Preferred Reporting Items for Systematic Reviews and Meta-Analysis system was followed.

A total of 33 studies published in English met the inclusion criteria. Thirty-one studies reported quantitative data, one was qualitative and one was mixed methods. Intervention effects on swallowing function, swallowing safety and swallowing-related quality of life were reported for various treatment approaches. Three studies explored how participants perceived the intervention. Overriding themes including subjects' views regarding treatment schedules and levels of effort or comfort associated with the intervention were identified across these studies. Combining evidence of intervention effects and subjects' experiences was possible for one rehabilitative and one compensatory intervention.

Beneficial effects of swallowing interventions have been reported; however, most experiments were case studies of variable methodological quality. Randomized-controlled trials with robust methodology to explore treatment effects in larger samples is needed to guide clinical practice. Research reporting subjects' views is scarce. More studies exploring how individuals perceive behavioural interventions for swallowing are necessary to inform clinical decision-making.

What is already known on the subject Dysphagia is common in individuals with PD. Swallowing intervention is of major importance as dysphagia may negatively affect physical and psycho-social health of subjects with PD. What this study adds Beneficial effects of behavioural interventions for swallowing, including rehabilitative and compensatory strategies, have been reported; however, available data are mostly based on case studies of variable quality. Data on how participants perceive specific behavioural interventions are lacking. Based on the available data, integration of efficacy data and individuals' experiences is limited. What are the clinical implications of this work? Given the current evidence of intervention effects and individuals' views on behavioural treatment strategies, interventions implemented into clinical practice require careful evaluation on a case-by-case basis. More high-quality research is needed to examine interventions' short- and long-term effects in larger samples to guide clinical practice. In addition to studies evaluating intervention effects, research exploring participants' experiences with interventions is required as a foundation for clinical decision-making.