OBJECTIVES: To evaluate the psychometric performance of Itch, Pain, and Burning Numeric Rating Scales (NRS) in a plaque psoriasis clinical trial.

METHODS: In a 12-week multi-center, randomized, double-blind, placebo-controlled study to assess a new psoriasis treatment, subjects completed Itch, Pain, Burning NRSs, and other assessments on an electronic daily diary. Each of the Itch, Pain, and Burning NRSs are single items asking respondents to rate their symptom “at its worst” in the 24 hours prior to assessment on a 0-10 NRS (0=no symptom, 10=worst possible symptom) and could be scored as a daily mean. Daily mean scores were analyzed descriptively and characterized with respect to test-retest reliability, construct-related validity, and sensitivity to change.

RESULTS: Participating in the study were N=208 subjects (52.9% female, 86.5% White/Caucasian) between the ages of 19 and 82 years (M=51.0, SD=14.5) who were designated as “mild” (n=39, 18.8%) or “moderate” (n=169, 81.3%) on an Investigator Global Assessment (IGA) of psoriasis and reported moderate itch (M=7.4, SD=1.2 on the Itch NRS). Subject responses were well distributed across the response scales. Observed intraclass correlations coefficients (ICC) among four prespecified no-change groupings for Itch (ICC range=0.32-0.73), Pain (ICC range=0.62-0.87), and Burning (ICC range=0.66-0.82) scores support adequate test-retest reliability in most instances. Correlations between the Itch-NRS and other global measures of pruritis (r’s>0.80) and between Itch, Pain, and Burning NRSs (r’s>0.50) and indicators of disease impact were among many of the correlational hypotheses met in the study. Evidence of score sensitivity is found in the moderate correlations between change in Itch (r=0.44), Pain (r=0.42), and Burning (r=0.34) NRS scores and change in a patient global measure of symptom severity from Baseline to Week 12.

CONCLUSIONS: The Itch, Pain, and Burning NRSs are capable of producing reliable and valid scores when administered to plaque psoriasis patients participating in a clinical trial.