Development and content validity of the Functional Impacts of Narcolepsy Instrument: a novel patient-reported outcome measure for narcolepsy type 1 and type 2

Abstract Study Objectives Most patient-reported outcome measures for narcolepsy focus on excessive daytime sleepiness or do not focus on specific disease impacts (e.g. cataplexy, cognitive difficulties, fatigue, daily function). The Functional Impacts of Narcolepsy Instrument (FINI) was developed to measure key functional impacts in people with narcolepsy type 1 and 2 (NT1/NT2). Methods The instrument was developed separately in NT1/NT2 populations with input from patients, clinical experts experienced in narcolepsy management, and clinical outcome scientists. Development included: patient experience interview studies informing item development; item development including de novo items, and modified/original items from the Patient-Reported Outcomes Measurement Information System (PROMIS) library; two waves of patient-debriefing interviews testing initial/modified item drafts; determination of scale structure using exploratory factor and Rasch analyses, and confirmatory factor analyses for NT2; consensus meetings between clinical sleep experts/clinical outcome experts to finalize the FINI draft items and structure with a 7-day recall period. Results The final FINI for NT1 had 28 items within six independent domains: Tiredness, Cognitive Functioning, Cataplexy, Social Activities, Everyday Activities, and Everyday Responsibilities. The final NT2 version (FINI-NT2) included the same items excluding the Cataplexy domain (23 items). Final FINI and FINI-NT2 items demonstrated good content validity and covered the main impacts of NT1 and NT2, respectively, as confirmed by patient interviews, exploratory/confirmatory factor analyses, and Rasch analysis. Conclusions The novel FINI assesses key functional impacts of narcolepsy in people with NT1/NT2 for use across clinical settings, and adds to the number of existing clinical outcome assessments for central disorders of hypersomnolence. Statement of Significance People with narcolepsy type 1 (NT1) or narcolepsy type 2 (NT2) often experience impacts on their daily life, such as cognitive difficulties, fatigue, and impaired work/school responsibilities, leading to decreased quality of life. Despite these recognized challenges, there remains a need for an additional tool that measures functional outcomes and complements existing narcolepsy symptom, severity, and impacts assessments. The Functional Impacts of Narcolepsy Instrument (FINI) was developed to evaluate functional impacts of narcolepsy that are important and meaningful to people living with NT1 (FINI) and NT2 (FINI-NT2). The instrument offers a patient-centered outcome measure for assessing narcolepsy impacts and treatment benefits related to changes in functional outcomes that can be used in both the clinical trial setting and clinical practice.