Quantitative method for measuring therapeutic efficacy of the 308 nm excimer laser for vitiligo

Abstract

Background There are several available treatments for vitiligo, but measurement of their therapeutic efficacy is not standardized and is somewhat arbitrary based largely on the global impression of the overall response. The purpose of this study was to develop a quantitative method for evaluating the treatment response of vitiligo measuring changes in area using digital image analysis. We applied this parametric model to the evaluation of efficacy of the 308 nm excimer laser.

Methods This study was a retrospective study, designed as a before and after trial with a single arm. A total of 18 patients were enrolled who had been treated with a 308 nm excimer laser as monotherapy twice a week for 20 sessions. The repigmentation percentage was calculated by measuring changes in area before and after treatment using digital image analysis and graded on a five-point ordinal scale [global assessment scale (GAS)]. GAS was also measured by physician and patient for comparison with our estimates. Additional GASs were also measured by four different evaluators for inter-rater variability.

Results The mean repigmentation percentage after treatment was 45.3% (range, 0.7100%). The changes in area after treatment were statistically significant (P ˂ 0.05). A substantial agreement of outcomes was observed between physicians and digital image analysis (kappa(w) = 0.78), but lower agreement was observed between patients and digital image analysis (kappa(w) = 0.49). The inter-rater variability for GAS was substantially low (Krippendorff's alpha = 79.3%).

Conclusion Measurement of changes in area using digital image analysis could be used as a quantitative method in evaluating efficacy of treatment for vitiligo. Because vitiligo lesions can occur in any location with various shapes and sizes, digital image analysis would be a more objective method for measuring treatment response than a GAS.