Fatigue numeric rating scale validity, discrimination and responder definition in patients with psoriatic arthritis

Abstract

Objectives: This study assessed the psychometric properties of the fatigue numeric rating scale (NRS) and sought to establish values for clinically meaningful change (responder definition).

Methods: Using disease-specific clinician-reported and patient-reported data from two randomised clinical trials of patients with psoriatic arthritis (PsA), the fatigue NRS was evaluated for test-retest reliability, construct validity and responsiveness. A responder definition was also explored using anchor-based and distribution-based methods.

Results: Test-retest reliability analyses supported the reproducibility of the fatigue NRS in patients with PsA (intraclass correlation coefficient=0.829). Mean (SD) values at baseline and week 2 were 5.7 (2.2) and 5.7 (2.4), respectively. Supporting construct validity of the fatigue NRS, moderate-to-large correlations with other assessments measuring similar concepts as measured by Sackett's conventions were demonstrated. Fatigue severity was reduced when the underlying disease activity was improved and reductions remained consistent at week 12 and 24. A 3-point improvement was identified as being optimal for demonstrating a level of clinically meaningful improvement in fatigue NRS after 12-24 weeks of treatment.

Conclusions: Fatigue NRS is a valid and responsive patient-reported outcome instrument for use in patients with PsA. The established psychometric properties from this study support the use of fatigue NRS in clinical trials and in routine clinical practice. Robust validation of reliability for use in routine clinical practice in treating patients with active PsA in less active disease states and other more diverse ethnic groups is needed.

Keywords: outcomes research; patient perspective; psoriatic arthritis.

Conflict of interest statement

Competing interests: DG received research grant support and/or consulting fees from Abbvie, Amgen, BMS, Celgene, Eli Lilly and Company, Janssen, Novartis, Pfizer and UCB. PN has received grants for research and for clinical trials and honoraria for advice and lectures from AbbVie, Amgen, BMS, Celgene, Eli Lilly and Company, Janssen, MSD, Novartis, Pfizer, Roche, Sanofi and UCB. HG has received fees for speaking and/or consulting from Abbie, Asahi Kasei, Astellas, Chugai, Eisai, Eli Lilly and Company, Janssen, Mitsubishi Tanabe, Ono, Pfizer, Santen, Takeda, and received research funding to Osaka City General Hospital from AbbVie, Chugai, Eisai, Eli Lilly and Company, Janssen, Sanofi and Santen. A-MO received research grant support and/or consulting fees from Celgene, Eli Lilly and Company, Horizon, Janssen, Novartis, Pfizer and UCB. TKK has received fees for speaking and/or consulting from AbbVie, Biogen, BMS, Boehringer Ingelheim, Celgene, Celltrion, Eli Lilly and Company, Epirus, Hospira, Merck-Serono, MSD, Mundipharma, Novartis, Oktal, Orion Pharma, Hospira/Pfizer, Roche, Sandoz, and UCB and received research funding to Diakonhjemmet Hospital from AbbVie, BMS, MSD, Pfizer, Roche and UCB. JB and C-YL are full-time employees of and hold stock/stock options in Eli Lilly and Company.

© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

Figures

Figure 1

Change from baseline in fatigue numeric rating scale (NRS) score was evident in associations with week 12 and 24 ACR outcomes (NRI), intent-to-treat population, last observation carried forward. Effect size is defined as the magnitude of change from baseline divided by baseline SD. ‡p<0.001 versus anchor not met, from analysis of covariance model, including anchor status and baseline fatigue NRS score. ‘Anchor’ refers to ACR50 or 20 responder if ‘anchor met’, and non-responder if ‘anchor not met’. ACR20, American College of Rheumatology 20% response rate; ACR50, American College of Rheumatology 50% response rate; ES, effect size; NRI, non-responder imputation.