Validation of a Patient Global Assessment for extent, severity and impact to define the severity strata for the Self Assessment Vitiligo Extent Score (SA-VES)

Background: The Self Assessment Vitiligo Extent Score (SA-VES) is a validated, patient-reported outcome measure to assess the body surface area affected with vitiligo. Information on how to translate the obtained score into extent, severity and impact strata (mild-moderate-severe) is still lacking. Stratification is helpful to define inclusion criteria for trials, enables comparison and pooling of trial results and can be used for epidemiological research.

Objectives: The aim was to develop extent, severity and impact strata for the SA-VES based on validated anchor-based questions.

Methods: In total, 315 patients with vitiligo (non-segmental; age ≥ 16) recruited at the Ghent University Hospital (Belgium) completed a questionnaire that was conducted in cooperation with the Dutch Society for vitiligo patients to ensure content validity. First three anchor questions included in the questionnaire [Patient Global Assessment (PtGA) for vitiligo extent, severity and impact] were assessed for content validity, construct validity and intrarater reliability. Subsequently, the PtGAs were used to stratify the SA-VES based on ROC analysis.

Results: For all PtGAs (PtGA extent, PtGA severity, PtGA impact), at least 75% of hypotheses evaluated for construct validity were confirmed. Intrarater reliability of all PtGAs was good to excellent (ICCs PtGA extent: 0.623; PtGA severity: 0.828; PtGA impact: 0.851). The optimal cut-off values of the SA-VES between the three global categories (mild/limited - moderate - severe/extensive) were 1.05% and 6.45% based on PtGA extent, 2.07% and 4.8% based on PtGA severity and 2% and 3.35% based on PtGA impact.

Conclusion: This study provides the first guide for the interpretation of the numerical output obtained by the SA-VES (vitiligo extent) and enables the translation into a global vitiligo grading for extent, severity and impact. As patients' interpretation of vitiligo extent, severity and impact may vary amongst patients worldwide, future international studies will be required.