Objective:

To evaluate psychometric properties of the Functional Impacts of Narcolepsy Instrument (FINI) using data from two narcolepsy studies.

Background:

Narcolepsy-specific tools assessing disease impact are currently lacking. The FINI is a novel 28-item patient-reported outcome (PRO) measure developed to evaluate treatment outcomes in people with narcolepsy types 1 and 2 (NT1/NT2).

Design/Methods:

FINI psychometric properties were evaluated using pooled data from an observational study (NT1, n=126) and a Phase 2 clinical trial (n=125; NCT04096560). Reliability, validity (convergent and known-groups) and sensitivity to change were evaluated; scale structure was defined and confirmed using exploratory factor analysis (EFA) and Rasch analysis. Meaningful within-patient change (MWPC) thresholds were defined using an anchor-based approach.

Results:

EFA results supported a 6-domain model (Tiredness, Cognitive Functioning, Cataplexy, Social Activities, Everyday Activities, and Everyday Responsibilities). Rasch analysis confirmed FINI’s multidimensionality with each domain independently assessing a core narcolepsy concept. FINI domains demonstrated good internal consistency (Cronbach’s alpha >0.77) and moderate-to-strong test-retest reliability (ICCs: 0.61–0.86). Known-groups validity was supported by higher domain scores with increasing severity ratings on the Epworth Sleepiness Scale (ESS), and Clinical/Patient Global Impression of Severity (CGI-S/PGI-S). Convergent validity was supported by strong correlations of FINI domains with other PROs assessing similar concepts (EQ-5D-5L, FOSQ-10, MFI, SF-36, and ESS). Sensitivity to change was supported by correlational analyses and categorical change group comparisons across clinical outcome assessments measuring similar concepts using symptom-specific (CGI-S/PGI-S) and change-specific (CGI/PGI of Improvement) anchors. MWPC thresholds were estimated as ranges: Tiredness (-30 to -40), Cognitive Functioning (-30 to -40), Cataplexy (-20 to -25), Social Activities (-30 to -40), Everyday Activities (-30 to -40), and Everyday Responsibilities (-25 to -35).

Conclusions:

FINI psychometric properties were confirmed and MWPC thresholds proposed for each domain. The FINI is a robust, valid measure to assess treatment benefit related to improvement in functional outcomes in people with narcolepsy.