Assessment of Content Validity and Psychometric Properties of the Wheal Intensity Likert Scale in Chronic Inducible Cold Urticaria

OBJECTIVES: Wheal Intensity Likert Scale (WILS) is a single-item clinician reported outcome measure rated from 0 (no wheals) to 5 (a large, very edematous wheal with pseudopodia), completed 10 minutes after an ice cube provocation test (ICPT). WILS was used in a phase 3 trial among chronic inducible cold urticaria (ColdU) patients treated with dupilumab or placebo (NCT04681729). This study aimed to generate evidence of content validity and psychometric properties of WILS.

METHODS: Five clinicians participated in one-to-one cognitive interviews to evaluate the understanding, appropriateness, and meaningful change of WILS. The psychometric properties were assessed in a sample of 82 ColdU patients from the phase 3 trial.

RESULTS: Clinicians understood the wording of WILS well and reported its appropriateness to be completed 10 minutes after ICPT (n=5/5). However, clinicians had some reservations about the complexity of WILS (n=2/5), appropriateness of terms (n=1/5) and subjectiveness of some terms, such as ‘large’ and ‘irregular’, that might be interpreted differently by physicians (n=3/5). Clinicians reported a 2-point (n=2/4) and 3-point (n=1/4) improvement to be clinically meaningful and n=1/4 considered this to be dependent on the patient’s baseline score. WILS score correlated well with ICPT score (absolute r=0.88) and adequately with Peak Burning Sensation-Numerical Rating Scale (PBS-NRS) and Patient Global Impression of Severity (PGIS) (absolute r range 0.51-0.75). Significant differences in WILS mean scores and PGIS level groups were observed (p<0.001). Responsiveness to change was demonstrated by moderate to strong correlations (r=0.44 to r=0.73), according to PGIS, ICPT and PBS-NRS. Anchor-based analysis suggested that 2-point reduction and 1-point reduction constitute meaningful within-patient and between-group thresholds for improvement, respectively.

CONCLUSIONS: WILS demonstrates good construct validity and responsiveness. However, due to clinician reservations, appropriate modifications would need to be considered to refine the instrument.