Worst Itch Numeric Rating Scale may Revolutionize Prurigo Nodularis Treatment Evaluation: JAMA

The secondary analysis of pooled data from the PRIME and PRIME2 clinical trials revealed that the Worst Itch Numeric Rating Scale may be a valid instrument for pruritus assessment in future clinical trials of prurigo nodularis.

“WI-NRS was a fit-for-purpose and valid instrument to support the efficacy endpoints of clinical trials in prurigo nodularis patients,” the researchers reported. “WI-NRS demonstrated good evidence of reliability, validity, and sensitivity to change. The clinically meaningful within-patient improvement threshold was 4 points.” The findings were published online in JAMA Dermatology on June 12, 2024.

The Worst Itch Numeric Rating Scale, a simple yet powerful tool, allows patients to rate the intensity of their worst itch on a numerical scale. By providing a standardized measure of itch severity, this scale enables clinicians to more accurately assess the effectiveness of treatments and tailor interventions to individual patient needs.

Shawn G. Kwatra, Johns Hopkins Medical Institutions, Baltimore, Maryland, and colleagues aimed to validate the psychometric properties and determine the clinically meaningful improvement threshold for WI-NRS in patients with moderate to severe PN.

In the analysis, the researchers assessed the content validity of WI-NRS through in-depth patient interviews. Psychometric assessments used pooled data from masked, intention-to-treat (ITT) PN patients from randomized, double-masked, and placebo-controlled studies.

Psychometric assessments included known-groups validity, construct validity, test-retest reliability, and sensitivity to change in adult moderate-to-severe PN patients. Thresholds for meaningful within-patient WI-NRS score improvement were determined using anchor and distribution-based approaches.

The patients were given dupilumab (300 mg) or placebo subcutaneously every two weeks for 24 weeks. The study’s main outcome was WI-NRS score at specified time points for 24 weeks after randomization.

The following were the key findings of the study:

• Twenty patients were included across the 2 studies (mean age, 49.3 years; 55% females); 311 patients were included in the pooled intention-to-treat analysis (mean age, 49.5 years; 65.3% females).
• The WI-NRS questions (20 of 20 patients), response scale (20 of 20 patients), and recall period (19 of 20 patients) were easy to understand and relevant for patients with PN.
• Adequate test-retest reliability was observed between screening and baseline (intraclass correlation coefficient = 0.72, using Patient Global Impression of Severity [PGIS] to define stable patients).
• Convergent and discriminant validity was supported by moderate to strong correlations with other conceptually related measures and weaker correlations with less related measures, respectively.
• WI-NRS was sensitive to change, as shown by differences in change from baseline among groups (per PGIS change and PGI of Change [PGIC]).
• Using an anchor-based approach with PGIS and PGIC, the clinically meaningful improvement threshold was 4 points, also supported by distribution-based methods.

“The study found that WI-NRS may be a fit-for-purpose instrument to support efficacy endpoints measuring itching intensity in adults with Prurigo Nodularis,” the researchers wrote.

Reference:

Kwatra SG, Yosipovitch G, Kim B, et al. Worst Itch Numeric Rating Scale for Prurigo Nodularis: A Secondary Analysis of 2 Randomized Clinical Trials. JAMA Dermatol. Published online June 12, 2024. doi:10.1001/jamadermatol.2024.1634