Background The assessment of the individual evolution of vitiligo is important for therapeutic decision making in daily practice. A fast, simple and validated physician-reported score to assess clinical changes in depigmentation over time in separate parts (activity and improvement) is currently missing.Objective The main objective of the study was to develop and validate the Vitiligo Disease Activity Score (VDAS) and Vitiligo Disease Improvement Score (VDIS).Methods The Vitiligo Disease Activity Score (VDAS) and Vitiligo Disease Improvement Score (VDIS) were evaluated based on a photo set of 66 patients with two different time points. In the first (short) version, only the number of changing body regions was counted based on 15 predefined areas (VDAS 15 and VDIS 15 ), while in the second (extensive) version the degree of worsening or improvement from +4 to À4 for each body area was added for a more detailed assessment (VDAS 60 and VDIS 60 ). Content and construct validity were tested. In addition inter-, intrarater reliability and feasibility were evaluated by 7 (test) and 5 (retest) physicians.Results Evidence for content and construct validity was provided. Overall, VDAS 15 , VDIS 15 , VDAS 60 and VDIS 60 demonstrated good to excellent inter-rater reliability [intraclass correlation (ICC): VDAS: range = 0.797-0.900; VDIS: range = 0.726-0.798]. The intrarater reliability ICCs were 0.865 and 0.781 for the VDAS 15 and VDIS 15 , respectively. Similar results were obtained for the VDAS 60 and VDIS 60 (ICC = 0.913 and 0.800, respectively). Completion time was short (median: 122 s/patient (first round); 95 s/patient (second round)].Limitations Single tertiary centre mainly of skin phototype 2 to 3. ConclusionThe VDAS and VDIS appear to be valid, reliable and feasible instruments to score the evolution of vitiligo lesions. This accommodates the current urgent need for a simple, standardized and practical assessment of vitiligo activity and improvement over time.

This study confirmed the reliability, validity and feasibility of two functions in ImageJ to measure target lesions in vitiligo. Based on the feasibility and included three-dimensional aspects, transparent sheets measured with the ImageJ 'wand' function can be proposed for future trials as a reference method to investigate the criterion validity of other digital instruments.

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