Development of a user guide to support administration of the MRC Prion Disease Rating Scale in research and clinical settings for prion diseases.

Background: The prion diseases (PrD) are a group of progressive, fatal, neurodegenerative diseases, for which the Medical Research Council Prion Disease Rating Scale (MRC Scale) can be used to assess patients' functional deterioration. Findings from previous qualitative interviews with caregivers and clinical experts identified potential ambiguities in the scale that could lead to inconsistent scoring within and/or between raters.

Methods: A draft User Guide was developed based on findings from a previous qualitative study. The draft included clarifications regarding domain wording, scoring levels, and guidance for response option selection. Five clinical experts with PrD management experience provided written feedback on the draft User Guide, which was incorporated into a revised User Guide. A 90-minute consensus meeting was then held with these experts to confirm the final content to be included in the User Guide.

Results: The final User Guide was designed to accompany the MRC Scale and assist with rater decisions related to which response option most accurately describes a patient's health status. Conclusions: The User Guide is expected to be a valuable complement to the MRC Scale, which is poised to rise in use and prominence as global clinical research efforts accelerate to address the significant unmet need of PrD patients.