Assessing Itch Severity: Content Validity and Psychometric Properties of a Patient-Reported Pruritus Numeric Rating Scale in Atopic Dermatitis.

Abstract

Pruritus, or itch, is a key symptom of atopic dermatitis (AD); as such, mitigating itch is an important outcome of AD treatment. This study explored the content validity and measurement properties of the Pruritus Numeric Rating Scale (Pruritus NRS), a novel single-item scale for assessing itch severity in clinical trials of AD treatments. In this mixed-methods study, qualitative interviews were conducted with 21 people with moderate-to-severe AD (n = 15 adult, n = 6 adolescent) to develop a conceptual model of the patient experience in AD and explore the content validity of the Pruritus NRS. Data collected daily from adults with moderate-to-severe AD enrolled in a phase2b study (NCT03443024) were used to assess the Pruritus NRS' psychometric performance, including reliability, construct validity, and responsiveness. Meaningful within-patient change (MWPC) thresholds were also determined using anchor-based methods. Qualitative findings highlighted the importance of itch in AD, including severity, persistence, frequency, and daily life interference. Patient debriefing of the Pruritus NRS indicated that the scale was relevant, appropriate, and interpreted as intended. Trial data supported overall good psychometric properties. MWPC was defined as a 3-point improvement in Pruritus NRS score, a finding supported by qualitative data. The Pruritus NRS provides a valid and reliable patient-reported measure of itching severity in patients with moderate-to-severe AD, and can detect change, indicating it is fit-for-purpose to evaluate the efficacy of AD treatments in this population. ClinicalTrials.gov identifier, NCT03443024.