Motor Fluctuations and Deep Brain Stimulation in Parkinson's Disease: A Cornerstone Indication with a Fragile Evidence Base? A Scoping Review of Randomized Controlled Trials

Deep Brain Stimulation (DBS) is an established treatment for Parkinson's disease (PD), indicated when troublesome motor fluctuations or levodopa-induced dyskinesias persist despite best medical treatment (BMT). Although these symptoms represent the core clinical indication for DBS, it is unclear how consistently they have actually been measured in the randomized controlled trials (RCTs) that established DBS efficacy. This scoping review maps how motor fluctuations and dyskinesias have been assessed as outcomes across RCTs of DBS in PD, asking: whether they were assessed; when assessed, whether as primary or secondary endpoints; and which tools were used to measure them. Following JBI methodology and PRISMA-ScR reporting, a systematic search will be conducted including peer-reviewed RCTs comparing DBS plus BMT with BMT alone or sham/suboptimal stimulation in adults with PD. Two reviewers will independently screen records and chart data (design, sample characteristics, intervention/comparator, and outcome measures such as UPDRS-III/-IV, MDS-UPDRS, PDQ-39, dyskinesia scales, and LEDD), with a third reviewer resolving disagreements. Given the expected heterogeneity in trial design and outcome reporting, no meta-analysis is planned; results will be presented narratively and in tabular form. The expected outcome is a clear picture of how adequately the symptoms justifying DBS have been evaluated in its supporting evidence base, highlighting methodological gaps for future trials.