Psychometric properties of the itch numeric rating scale, skin pain numeric rating scale, and atopic dermatitis sleep scale in adult patients with moderate-to-severe atopic dermatitis

Background

The Itch Numeric Rating Scale (NRS), Skin Pain NRS, and Atopic Dermatitis Sleep Scale (ADSS) are self-administered patient-reported outcome (PRO) instruments developed to assess symptoms in patients with atopic dermatitis (AD). The objective of this study was to evaluate the psychometric properties (reliability, validity, and responsiveness) and interpretability thresholds of these PROs using data from three pivotal Phase 3 studies in adults.

Methods

BREEZE-AD1, BREEZE-AD2, and BREEZE-AD5 evaluated the safety and efficacy of baricitinib in adults with moderate-to-severe AD. Clinician-reported outcomes and other PROs commonly assessed in patients with AD were used to estimate meaningful changes and evaluate test–retest reliability, convergent and divergent validity, known-groups validity, responsiveness, and meaningful change thresholds (MCTs) of the Itch NRS, Skin Pain NRS, and ADSS.

Results

The test–retest reliability of the Itch NRS, Skin Pain NRS, and ADSS was evidenced by generally large intraclass correlation coefficients (> 0.7) in stable groups of patients between baseline and Week 1 and Weeks 4 and 8. Moderate-to-large correlations (r > 0.4) at baseline and Week 16 were generally observed between each measure and other PROs measuring the same concept, supporting convergent validity. Small-to-moderate correlations with clinician-reported outcomes demonstrated divergent validity. Each instrument was able to distinguish between known groups of disease severity as assessed using other indicators of AD severity. The responsiveness of the Itch NRS, Skin Pain NRS, and ADSS scales was demonstrated through significant differences in their change scores from baseline to Week 16 between categories of change in another PRO also from baseline to Week 16. Thresholds for interpreting meaningful change were estimated as − 4.0 for the 0–10 Itch and Skin Pain NRS items; − 1.25 for the 0–4 ADSS Items 1 and 3 and; − 1.50 for the 0–29 ADSS Item 2, these equivalent to moderate degrees of change.

Conclusions

Results of this study demonstrate that the psychometric properties of the Itch NRS, Skin Pain NRS, and ADSS are good to excellent. These findings support the use of these instruments in daily assessment of AD symptoms in adults with moderate-to-severe AD.

Trial registration ClinicalTrials.gov numbers: NCT03334396, NCT03334422, and NCT03435081.

Exploring content and psychometric validity of newly developed assessment tools for itch and skin pain in atopic dermatitis

Background

Atopic dermatitis (AD) is a common skin disorder characterized by chronic inflammation, altered skin barrier function, and inflammatory cell skin infiltration that decreases health-related quality of life (HRQoL). The study objective was to understand the patient perspective of AD burden and determine suitable patient-reported outcome (PRO) measures.

Methods

This mixed methods study involved the collection of qualitative and quantitative information from adults (≥ 18 years old) and adolescents (12 – 17 years old) with clinician-confirmed AD regarding their experiences of AD symptoms and its impact on HRQoL. The first part of the study included three stages: in-person concept elicitation (CE) interviews, a 2-week daily electronic diary (eDiary) study, and in-person cognitive debriefing (CD) interviews. An Itch numeric rating scale (NRS) (v1.0) and a Skin Pain NRS (v1.0) evaluation during CD interviews required participants to think about their ‘worst’ itch and ‘worst’ skin pain in the past 24 h. Other PRO measures allowed for psychometric testing. The second part of the study involved telephone-depth interviews (TDIs) and qualitative feedback from participants who had not participated in the CD interviews. Qualitative data were thematically analyzed. Psychometric evaluation of NRS measures was performed using eDiary data.

Results

In the CE interviews, itch and/or itching and skin pain were the most prevalent symptoms consistently discussed by participants. Both NRS measures demonstrated strong psychometric reliability and were applicable across ages with suitable concurrent validity. During the CD interviews, some participants focused their answers on their ‘average’ itch/itching in the past 24 h, rather than their ‘worst’ itch. Some participants answered the Skin Pain NRS thinking about general pain or other types of pain, rather than skin pain specifically. Consequently, modifications to both measures addressed these issues and re-tested as paper-and-pen versions in subsequent TDIs. Itch NRS (v2.0) modifications helped participants focus on their worst itching. Most participants preferred Skin Pain NRS v2.0b, which included skin pain descriptors.

Conclusions

Itching and skin pain are the most important and relevant AD symptoms. The Itch NRS (v2.0) and Skin Pain NRS (v2.0b) appear to be appropriate endpoints for the assessment of itching and skin pain severity for clinical trials with adults and adolescents with AD.