Functional Rating Scale 2.0 (FuRST 2.0): A patient-reported outcome measure of function for Huntington's disease.

BackgroundCurrent functional rating scales are not sensitive to the earliest functional changes in Huntington's disease (HD).ObjectiveThe Functional Rating Scale 2.0 (FuRST 2.0) is a patient-reported outcome (PRO) measure designed to be sensitive to the initial functional changes in HD, specifically stage 2 and mild stage 3, as defined by the Huntington's Disease Integrated Staging System (HD-ISS).MethodsWe followed standard assessment development methodology to create a PRO. Study 1 consisted of a Delphi panel which analyzed data from focus groups comprised of people with HD and companions from 6 countries. This was followed by four rounds of cognitive interviews through which we evaluated respondents' comprehension of the instructions, understanding of question and response options, and comfort with the material. Informal advice from a regulatory agency was garnered throughout the process.ResultsConcerns from the target population and regulators regarding instructions, questions, response options, and comfort with the material were addressed through modifications to the scale's wording and format.ConclusionsWe developed the FuRST 2.0 official working document (OWD), the penultimate version of the scale, using focus groups, a Delphi panel, iterative rounds of cognitive interviewing, and informal regulatory advice. Its psychometric properties are being evaluated in the FOCUS-HD validation studies from which the final version of the scale will be derived. The FuRST 2.0 OWD is available for use.