Psychometric evaluation of worst pruritus numeric rating scale in adults with moderate-to-severe atopic dermatitis

Abstract

INTRODUCTION: Atopic dermatitis (AD) is a chronic, inflammatory skin disease with a hallmark symptom of pruritus. We developed Worst Pruritus Numeric Rating Scale (NRS)-a single-item, patient-reported outcome measure-to assess itch severity in clinical trial populations of adults with moderate-to-severe AD. The objective of this study was to evaluate the psychometric properties of Worst Pruritus NRS and determine its appropriateness for use in clinical trials assessing the efficacy of treatments among adults with moderate-to-severe AD.

METHODS: We used data from a subset of 267 participants in a phase 2 clinical trial of rocatinlimab (NCT03703102; N = 274) to confirm reliability, validity, and ability to detect change in Worst Pruritus NRS. We estimated and confirmed a meaningful within-patient change (MWPC) threshold using anchor- and distribution-based methods.

RESULTS: All intraclass correlation coefficients (ICCs) were ≥ 0.86, providing robust evidence for test-retest reliability. Evidence supported construct validity, including known-groups validity (all P < 0.0001). There were moderate, positive correlations between scores on Worst Pruritus NRS and supportive measures at week 16, including Dermatology Life Quality Index (DLQI) question 1 (itch item) (r = 0.78), DLQI (r = 0.66), Eczema Area and Severity Index (EASI) (r = 0.50), Investigator's Global Assessment (IGA) (r = 0.46), Body Surface Area of Involvement (BSA) (r = 0.40), and SCORing Atopic Dermatitis (SCORAD) itch item (r = 0.97). On average, patients with better DLQI question 1 scores, EASI, and IGA classifications achieved better (i.e., lower) scores on Worst Pruritus NRS at week 16 (P < 0.0001). Ability to detect change was supported with moderate-to-strong and positive correlations between Worst Pruritus NRS change scores and changes in supporting measures. MWPC estimates confirmed the commonly applied 4-point threshold value and a range of 3 to 4 points as indicative of meaningful within-patient change.

CONCLUSIONS: Worst Pruritus NRS is a reliable and valid patient-reported outcome measure to assess itch severity in clinical trial settings among adults with moderate-to-severe AD.