OBJECTIVE: To present the validation analyses of the Peak Pruritus Numerical Rating Scale (PP-NRS) for measuring itch in patients with moderate-to-severe atopic dermatitis (AD).
METHODS: PP-NRS is a single, self-completed item to assess the intensity of peak (worst) pruritus during the past 24 h. Content validation included interviews with US adults with AD self-reporting moderate-to-severe itch (n = 14). Psychometric evaluation included cross-sectional (construct; known-groups validity) and longitudinal (test-retest; sensitivity to change) analyses. These were assessed in a 16week phase 2b (P2b) study (N = 379; NCT01859988) and confirmed using pooled data from two phase 3 (P3) studies (N = 1,379; NCT02277743, NCT02277769) in adults with moderate-to-severe AD.
RESULTS: Interview participants found the PP-NRS relevant, clear, and comprehensive. In P2b large positive baseline correlations were observed between PP-NRS and measures of similar constructs (Average Pruritus NRS [r = 1.00], SCORAD itch VAS [r = 0.77], Dermatology Life Quality Index (DLQI) itch item [r = 0.67], p < 0.01 for all), and weak-to-moderate correlations with measures of different constructs (EASI [r = 0.09] and Investigator’s Global Assessment (IGA) [r = 0.17, p < 0.01]), confirmed in P3. PPNRS differed predictably and significantly across known groups (p < 0.0001) in P2b/P3. Intraclass correlation coefficients of the test-retest analysis were ≥0.95 in P2b/P3. Moderate-to-strong correlations of change were observed between PP-NRS and SCORAD itch VAS (P2b/P3; r = 0.77/ 0.73), DLQI itch item (r = 0.66/0.64), PCS (r = 0.71/0.72), EASI (r = 0.50/0.46), and IGA (r = 0.50/0.46) (all p < 0.01).
CONCLUSIONS: Peak Pruritus NRS is a well-defined, reliable, sensitive, and valid scale to assess itch intensity in adult patients with moderate-to-severe AD.
