Reference method for digital surface measurement of target lesions in vitiligo: a comparative analysis

Background Objective measurement of target lesions in vitiligo is important for clinical practice and trials, yet no preferred tool has been defined. Reported digital tools have shortcomings related to feasibility aspects and often lack information on validity, reliability and responsiveness. Moreover, studies are not yet based on ultraviolet (UV) photography. Objectives To assess the reliability, validity and feasibility of two functions in ImageJ for measurement of target lesions, based on three different types of images including UV pictures. Methods Planimetric measurements were performed on photographs with and without UV, and lesion contours on transparent sheets of 52 vitiligo lesions from 10 patients with vitiligo. The ImageJ functions 'wand' and 'threshold' were used by three and four assessors, respectively. Inter- and intrarater reliability, hypothesis testing for construct validity, and feasibility were evaluated. Results The inter- and intrarater reliability for the 'wand' and 'threshold' functions were excellent [intraclass correlation coefficient (ICC) > 0 center dot 9] for measurement on pictures (with or without UV). The highest agreement (ICC > 0 center dot 95) and lowest variance were obtained for measurements on transparent sheets. All four hypotheses for construct validity were confirmed for all measurements. Overall, all measurement methods scored satisfactorily for user-friendliness. However, measurements on transparent sheets were preferred and the completion time was significantly faster. Conclusions 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.