Psychometric Properties and Meaningful Change Thresholds of the Vitiligo Area Scoring Index.

Abstract

Importance: Defining meaningful improvement using the Total Vitiligo Area Scoring Index (T-VASI) and the Facial VASI (F-VASI) aids interpretation of findings from clinical trials evaluating vitiligo treatments; however, clear and clinically meaningful thresholds have not yet been established.

Objective: To assess concept validity and measurement performance of the T-VASI and F-VASI in patients with nonsegmental vitiligo and to identify meaningful change thresholds.

Design, settings, and participants: This mixed-methods study consisted of a secondary analysis of a phase 2 multicenter double-blind dose-ranging randomized clinical trial and embedded qualitative interviews conducted at 35 sites in Canada, France, Japan, and the US. The secondary analysis included the trial's adult patients with nonsegmental vitiligo (T-VASI ≥5 and F-VASI ≥0.5 at baseline). Psychometric performance of the T-VASI and F-VASI and thresholds for meaningful change were evaluated using clinician- and patient-reported information. The trial's embedded interviews were used to qualitatively assess content validity and patient perceptions of meaningful repigmentation. Data analyses were performed from March to July 2023.

Intervention: Participants were randomized to 6-, 11-, or 22-mg/day upadacitinib or placebo for 24 weeks.

Main outcomes and measures: Psychometric performance of the T-VASI and F-VASI and thresholds for meaningful changed plus content validity and patient perceptions of meaningful repigmentation. Measurement instruments included the T-VASI, F-VASI, Vitiligo Noticeability Scale, Total-Patient Global Vitiligo Assessment, Face-Patient Global Vitiligo Assessment, Total-Physician Global Vitiligo Assessment (PhGVA-T), Face-Physician Global Vitiligo Assessment (PhGVA-F), Patient's Global Impression of Change-Vitiligo, Physician's Global Impression of Change-Vitiligo (PhGIC-V), Vitiligo Quality-of-Life Instrument, Dermatology Life Quality Index, the Hospital Anxiety and Depression Scale, and transcribed verbatim interviews with patients.

Results: The psychometric analysis included 164 participants (mean [SD] age, 46 years; 103 [63%] females) and the qualitative analysis included 14 participants (mean [SD] age, 48.8 [12.2] years; 9 females [64%] and 5 males [36%]). Intraclass correlation coefficients were 0.98 for T-VASI and 0.99 for F-VASI in patients with clinically stable vitiligo between baseline and week 4, supporting test-retest reliability. At baseline and week 24, correlations were moderate to strong between T-VASI and PhGVA-T (r = 0.63-0.65) and between F-VASI and PhGVA-F (r = 0.65-0.71). Average baseline and week-24 VASI scores decreased with repigmentation (ie, increasing PhGVA scores). Least-square mean VASI scores increased with greater repigmentation as measured by the PhGIC-V. Least-square mean VASI scores also differed between patients with improved PhGIC-V and those with no change or worsened V-PhGIC scores. Using a multiple anchor approach, improvements of 30% in T-VASI and 50% in F-VASI scores reflected meaningful repigmentation between baseline and week 24.

Conclusion and relevance: This mixed-methods study found that the T-VASI and F-VASI are reliable, valid, able to differentiate between clinically distinct groups, and responsive in patients with nonsegmental vitiligo. The thresholds for meaningful change were lower than those historically used in clinical trials, suggesting that T-VASI 50 and F-VASI 75 are conservative estimates and reflect improvements that would be meaningful in patients with nonsegmental vitiligo.

Trial registration: ClinicalTrials.gov Identifier: NCT04927975.