Psychometric properties of the Itch Numeric Rating Scale in patients with moderate-to-severe plaque psoriasis

A. B. Kimball, A. N. Naegeli, E. Edson-Heredia, C. Y. Lin, C. Gaich, E. Nikaï, K. Wyrwich, Gil Yosipovitch

Research output: Contribution to journalArticle

34 Scopus citations

Abstract

Background: Itching is a profoundly distressing symptom for many patients with psoriasis, but it has not been rigorously studied using validated tools for this condition. Objectives: This study investigated the psychometric properties of the Itch Numeric Rating Scale (Itch NRS), a single-item patient-reported outcome (PRO) measuring the worst itching severity due to psoriasis in the past 24 h. Methods: Using disease-specific clinician-rated and PRO data from one phase II and three phase III randomized clinical studies of subjects with moderate-to-severe plaque psoriasis, the Itch NRS was evaluated for test–retest reliability, construct validity and responsiveness. A responder definition was explored using anchor- and distribution-based methods. Results: Test–retest reliability analyses supported the reproducibility of the measure (intraclass correlation coefficient range 0·71–0·74). To support the construct validity of the Itch NRS, large cross-sectional correlations with the Dermatology Life Quality Index (DLQI) Symptoms and Feelings domain (r ≥ 0·60 at baseline and r ≥ 0·80 at week 12) supported a priori hypotheses, while large correlations (r ≥ 0·71) between changes in Itch NRS scores and changes in DLQI Symptoms and Feelings domain scores from baseline to week 12 established responsiveness. A 4-point change was optimal for demonstrating a level of clinically meaningful improvement in itch severity after 12 weeks of treatment, which corresponds with marked clinical improvements in plaque psoriasis. Conclusions: The Itch NRS demonstrated sufficient reliability, validity and responsiveness, and appropriate interpretation standards for evaluating change over time in itch severity among patients with moderate-to-severe plaque psoriasis when validated using clinical trial data for this condition.

Original languageEnglish (US)
Pages (from-to)157-162
Number of pages6
JournalBritish Journal of Dermatology
Volume175
Issue number1
DOIs
StatePublished - Jul 1 2016
Externally publishedYes

ASJC Scopus subject areas

  • Dermatology

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