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.