The Sleep Disturbance Numerical Rating Scale: Content Validity, Psychometric Validation, and Meaningful Within-Patient Change in Prurigo Nodularis

Introduction Sleep is often disturbed in patients with prurigo nodularis (PN). To address the lack of validated patient-reported outcome (PRO) measures for quantifying sleep disturbance in PN, we evaluated the Sleep Disturbance Numerical Rating Scale (SD NRS) as a single-item PRO measure for quantifying sleep disturbance in PN. Methods Adults with PN participated in qualitative interviews, which included concept elicitation and cognitive debriefing of the SD NRS. The SD NRS was evaluated psychometrically using data from a phase 2 randomized trial in adults with PN (NCT03181503). Other PRO assessments included the Average Pruritus (AP) NRS, AP Verbal Rating Scale (VRS), peak pruritus (PP) NRS, PP VRS, and Dermatology Life Quality Index (DLQI). Reliability, validity, and responsiveness of the SD NRS were evaluated, and meaningful within-patient change was estimated from qualitative interview responses and quantitative trial data. Results All interview participants ( N = 21) experienced sleep disturbance and most (95%) understood the SD NRS as intended. The SD NRS demonstrated test–retest reliability based on intra-class correlation coefficients for itch-stable participants of 0.87 for the AP VRS and 0.76 for the PP VRS. At baseline, Spearman’s rank-order correlation coefficients were moderate to strong (0.3–0.8) between the SD NRS and the AP NRS, AP VRS, PP NRS, PP VRS, and DLQI. Known-groups validity was demonstrated by higher (worse) SD NRS scores in participants with worse scores on the AP NRS, AP VRS, PP VRS, and DLQI. Improvements in SD NRS scores were greater in participants classified as “improved” versus “worsened/unchanged” on the anchor PROs. A 2- to 4-point decrease on the 11-point SD NRS scale was identified as a meaningful within-patient change. Conclusion The SD NRS is a well-defined, reliable, and valid PRO measure that can be used in daily practice and clinical trials to capture sleep disturbance in adults with PN.