Assessing the minimal important change in the vitiligo extent score and the self-assessment vitiligo extent score
Authors: Sanne E. Uitentuis, Albert Wolkerstorfer, Jung Min Bae, Samia Esmat, Rania M. Mogawer, Nanis Ragab, Sai Yee Chuah, Thierry Passeron, Nanja van Geel, Steven T.G. Thng, Caroline B. Terwee, Marcel W. Bekkenk
Journal: Journal of the American Academy of Dermatology (2020)

To the Editor: There is a need for valid, reliable, and interpretable measurement instruments in vitiligo research.1Eleftheriadou V. Thomas K. van Geel N. et al.Developing core outcome set for vitiligo clinical trials: international e-Delphi consensus.Pigment Cell Melanoma Res. 2015; 28: 363-369Crossref PubMed Scopus (67) Google Scholar The Vitiligo Extent Score (VES) and Self-Assessment Vitiligo Extent Score (SA-VES) are validated, feasible, and user friendly measurement instruments assessing vitiligo extent.2van Geel N. Lommerts J. Bekkenk M. et al.Development and validation of the Vitiligo Extent Score (VES): an International Collaborative Initiative.J Invest Dermatol. 2016; 136: 978-984Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar,3van Geel N. Lommerts J.E. Bekkenk M.W. et al.Development and validation of a patient-reported outcome measure in vitiligo: the Self Assessment Vitiligo Extent Score (SA-VES).J Am Acad Dermatol. 2017; 76: 464-471Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar However, the minimal important change (MIC) of these instruments is not known—MIC is the smallest change in scores that patients (/clinicians) perceive as important.4de Vet H.C.W. Terwee C.B. Mokkink L.B. et al.Measurement in Medicine: A Practical Guide. Cambridge University Press, 2011Crossref Scopus (1584) Google Scholar The MIC is a key element of interpretability of measurement instruments and is an important parameter in studies for determining the number of responders. The MIC of vitiligo extent might differ for different locations and according to the surface area affected. The primary aim of this study was to determine the MIC of the VES and SA-VES. A secondary aim was to determine the MIC for vitiligo of the face and hands and for patients with limited vitiligo (<5% body surface area [BSA]). The methods of our study are described in supplement 1 (Available at https://data.mendeley.com/datasets/r32tby2nhy/1). A total of 135 patients (mean age, 42.3 years; 58.5% women) completed the study (Table I). We used an anchor-based method to determine the MIC in which a global question about perceived change is used as an external criterion (anchor) to determine whether extent of vitiligo has changed over time. Patients were divided into 6 subgroups according to the anchor questions. We found MICs of 0.5% and 0.2% BSA for the VES and SA-VES, respectively. The mean change scores for each subgroup for the VES and SA-VES are shown in supplements 2a and 2b (Available at https://data.mendeley.com/datasets/r32tby2nhy/1), respectively.Table IIncluded patients from each countryTotalNetherlandsEgyptSouth KoreaSingaporeIncluded16250 (30.9)42 (25.9)29 (17.9)41 (25.3)Lost to follow up27 (16.7)6 (12.0)5 (11.9)2 (6.9)14 (34.1)Completed135(of which 1 only VES and 4 only SA-VES data)44 (88.0)37 (88.1)27 (93.1)27 (65.9)(of which 1 only VES and 4 only SA-VES data)General characteristics Age (y)42.3 ± 15.343.6 ± 11.733.7 ± 16.751.2 ± 14.843.0 ± 13.8 GenderFemale79 (58.5)28 (63.6)21 (56.8)16 (59.3)14 (51.9)Male56 (14.5)16 (36.4)16 (43.2)11 (40.7)13 (48.1) Skin typeI2 (1.5)2 (4.5)000II21 (15.6)21 (47.7)000III45 (33.3)8 (18.2)12 (32.4)15 (55.6)10 (37.0)IV54 (40.0)5 (11.4)25 (67.6)12 (44.4)12 (44.4)V11 (8.1)6 (13.6)005 (18.5)VI2 (1.5)2 (4.5)000VES score at T03.5 ± 5.33.7 ± 6.34.6 ± 5.43.1 ± 4.92.1 ± 3.4SA-VES score at T04.3 ± 7.05.5 ± 9.84.6 ± 4.93.7 ± 5.82.5 ± 4.5Values are n (%) or mean ± standard deviation, VES and SA-VES scores are percentage body surface area.T0, Moment of inclusion. Open table in a new tab Values are n (%) or mean ± standard deviation, VES and SA-VES scores are percentage body surface area. T0, Moment of inclusion. The MIC for the VES (0.5%) is somewhat lower compared with the smallest detectable change (SDC; change in outcome that could be due to measurement error) found in 2 previous studies, which were already very low (between 0.86% and 4.7%).2van Geel N. Lommerts J. Bekkenk M. et al.Development and validation of the Vitiligo Extent Score (VES): an International Collaborative Initiative.J Invest Dermatol. 2016; 136: 978-984Abstract Full Text Full Text PDF PubMed Scopus (70) Google Scholar,5van Geel N. Wolkerstorfer A. Lommerts J.E. et al.Validation study of the Vitiligo Extent Score-plus.J Am Acad Dermatol. 2018; 78: 1013-1015Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar For the SA-VES, we found a smaller MIC (0.2% BSA) compared with the (also low) SDC of 3.23%. This finding means that a decrease in BSA measured by the VES/SA-VES as great as the MIC might be considered important for physicians/patients, but this change cannot be distinguished from measurement error with 95% confidence. The same applies to the MIC we found for patients with BSA less than 5%. For lesions on the face, we found a MIC of 0.16 for the VES and 0.22 for the SA-VES. The sample size of subgroups was not large enough to make comparisons of the MIC between countries or skin types. Future studies should aim to assess the MIC and SDC within the same patient population, including different ethnicities, to provide more representative results and could focus on further optimizations (eg, by use of VESplus) to reduce the SDC to become smaller than the MIC.5van Geel N. Wolkerstorfer A. Lommerts J.E. et al.Validation study of the Vitiligo Extent Score-plus.J Am Acad Dermatol. 2018; 78: 1013-1015Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar Patients seem to perceive even very small changes in BSA involvement as an improvement and that location and disease extent are important to consider when interpreting changes in VES and SA-VES. Our results improve the interpretability of these measurement instruments and can be used to determine number of responders in future studies using the VES and SA-VES as outcome instruments. We express our gratitude to the volunteering patients who participated in this study.