Towards the development of a core outcome set for post-stroke facial palsy (COS Post-Stroke Facial Palsy): a study protocol for establishing professional consensus on what to measure

<b>Background:</b> Facial palsy affects 45-60% of acute stroke patients, significantly impacting their physical function, communication, and quality of life. Varied outcome measures across studies and clinical practices make it difficult to synthesise evidence and establish treatment effectiveness. This protocol describes in detail the professional stakeholder component of a multistage Core Outcome Set (COS) development programme for post-stroke facial palsy. This component focuses on identifying critically important outcomes (the “what” to measure) between two key stakeholder groups: clinicians and researchers.<br/><br/><b>Methods:</b> This study follows the Core Outcome Set standards for development (COS-STAD) and protocol (COS-STAP) recommendations. The development process consists of five sequential steps: (1) outcome generation through systematic reviews, consultation with our co-researchers who have lived experience and the findings from qualitative interviews with stroke participants, (2) recruitment of up to 200 international clinicians and researchers (minimum 30 per group) through clinical networks (including professional associations), social media platforms (X, LinkedIn, Bluesky) and via published research identifying stroke and facial palsy researchers, (3) multiple rounds of Delphi surveys, (4) online consensus meeting (at least five per stakeholder group), and (5) results dissemination. <br/><br/><b>Discussion:</b> This paper reports the detailed protocol for the professional stakeholder component, which will establish consensus among clinicians and researchers on what outcomes are critically important to measure. This protocol addresses a significant gap in stroke rehabilitation research as part of a comprehensive, multi-stage programme to develop a COS for post-stroke facial palsy. Standardising outcome measurement will facilitate more effective synthesis of research findings, reduce research waste, and accelerate intervention development. It describes how people with lived experience have been included from the start and signposts to a parallel study using the supported nominal group technique (detailed protocol reported separately). A parallel systematic review will evaluate available measurement instruments, their psychometric properties to explore ‘how’ to measure the agreed outcome domains. The results of each stage will be disseminated through multiple channels to facilitate widespread research and clinical practice adoption.<br/><br/><b>Trial Registration: </b>Core Outcome Measures in Effectiveness Trials (COMET) registered, December 2024 (https://www.comet-initiative.org/Studies/Details/3295); systematic review registered (PROSPERO), June 2023, CRD42023410768. <br/>