The Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) scale in patients with axial spondyloarthritis: psychometric properties and clinically meaningful thresholds for interpretation

J Patient Rep Outcomes. 2024 Aug 12;8(1):92. doi: 10.1186/s41687-024-00769-x.

Abstract

Background: Fatigue is an important symptom for most patients with axial spondyloarthritis (axSpA). The FACIT-Fatigue is a 13-item patient-reported outcome (PRO) instrument that has been used in axSpA clinical trials to measure fatigue severity and impact on daily activities. However, the psychometric properties of the FACIT-Fatigue are not fully evaluated across the entire spectrum of axSpA including non-radiographic axSpA (nr-axSpA) and radiographic axSpA (r-axSpA). This study determined: (1) the psychometric properties of the FACIT-Fatigue in nr-axSpA, r-axSpA, and the broad axSpA population and (2) FACIT-Fatigue scores representing meaningful within-patient change (MWPC), meaningful between-group differences, and cross-sectional severity bands.

Methods: Data from two Phase 3 trials in adults with nr-axSpA (BE MOBILE 1; N = 254) and r-axSpA (BE MOBILE 2; N = 332) were analyzed pooled and separately to assess the psychometric properties of the FACIT-Fatigue. MWPC and meaningful between-group difference estimates were derived using anchor-based and distribution-based methods. Cross-sectional fatigue severity bands were estimated using logistic regression analysis.

Results: The FACIT-Fatigue presented good internal consistency, adequate convergent and known-groups validity, and was sensitive to change over time across the full axSpA spectrum. A 5-11-point increase in FACIT-Fatigue score was estimated to represent a MWPC, with an 8-point increase selected as the responder definition. A 2.14-5.34-point difference in FACIT-Fatigue score change over a 16-week period was estimated to represent a small-to-medium meaningful between-group difference. FACIT-Fatigue score severity bands were defined as: none or minimal (>40), mild (>30 to ≤40), moderate (>21 to ≤30), and severe (≤21).

Conclusions: These findings support the use of the FACIT-Fatigue as a fit-for-purpose measure to assess fatigue-related treatment benefit in axSpA clinical trials. The proposed score estimates and thresholds can guide FACIT-Fatigue score interpretation across the full axSpA spectrum.

Trial registration: ClinicalTrials.Gov, NCT03928704. Registered 26 April 2019-Retrospectively registered, https://classic.

Clinicaltrials: gov/ct2/show/NCT03928704 .

Clinicaltrials: Gov, NCT03928743. Registered 26 April 2019-Retrospectively registered, https://classic.

Clinicaltrials: gov/ct2/show/NCT03928743 .

Keywords: Ankylosing spondylitis; Axial spondyloarthritis; FACIT-Fatigue; Fatigue; Meaningful between-group difference; Meaningful within-patient change; Non-radiographic axial spondyloarthritis; Psychometric properties; Severity bands.

Publication types

  • Clinical Trial, Phase III

MeSH terms

  • Adult
  • Axial Spondyloarthritis*
  • Cross-Sectional Studies
  • Fatigue* / diagnosis
  • Fatigue* / etiology
  • Female
  • Humans
  • Male
  • Middle Aged
  • Patient Reported Outcome Measures*
  • Psychometrics* / methods
  • Reproducibility of Results
  • Severity of Illness Index*

Associated data

  • ClinicalTrials.gov/NCT03928704
  • ClinicalTrials.gov/NCT03928743