Assessing the content validity of the 2015 core domain set for vitiligo clinical trials: preliminary investigations for developing an updated version

Background The 2015 core domain set (CDS) for vitiligo defines outcomes for clinical trials, comprising three essential and four recommended outcome domains/domain items. Periodic reassessment is required to ensure its continued relevance. Objectives To evaluate the content validity (relevance, comprehensiveness and comprehensibility) of the 2015 vitiligo CDS to inform a consensus-based update as part of a core outcome set, including core outcomes and core measurement instruments. Methods A roundtable discussion and three surveys reassessed the 2015 vitiligo CDS regarding relevance (≥ 70% agreement for ‘essential’), comprehensiveness (identification of missing domain items) and comprehensibility (clarity of terminology and descriptions). Results Fifty-three patients with vitiligo (group 1) and 37 experts (36 dermatologists and 1 researcher; group 2) participated. Two previously essential domains (‘Repigmentation’ and ‘Side effects/harms’) were re-endorsed as essential by both groups. ‘Maintenance of gained repigmentation’ was rated essential by patients only. Among previously recommended domains, ‘Quality of life’ was considered essential by both groups, whereas ‘Cosmetic acceptability of repigmentation’ and ‘Cessation of spreading of vitiligo’ were rated essential by patients only. ‘Tolerability/burden of treatment’ was not considered essential by either group. Frequently suggested missing items (outcomes and contextual factors) included psychological impact, treatment session duration, overall treatment duration, treatment costs, patient education and evaluation of associated auto­immune diseases. Proposed updates included refining domain terminology (e.g. vitiligo-specific/health-related quality of life; replacing ‘harms’ with ‘adverse events’) and addressing feasibility-related timeframes. Conclusions While the 2015 vitiligo CDS retains content validity for several domains, meaningful updates are warranted. These findings will inform the development of a revised and updated CDS.