Consensus opinion of a North American Working Group regarding the classification of digital ulcers in systemic sclerosis

Abstract

The objectives of this study were to develop a standard classification of digital ulcers (DUs) in systemic sclerosis (SSc) for use in observational or therapeutic studies and to assess the reliability of these definitions as well as of the measurement of ulcer area. Ten North American rheumatologists with expertise in SSc reviewed multiple photos of DUs, examined four SSc subjects with DUs, and came to a consensus on the definitions for digital, active, healed, and indeterminate ulcers. These ten raters then examined the right hand of ten SSc subjects twice and the left hand once to classify ulcers and to measure ulcer area. Weighted and Fleiss kappa were used to calculate intra- and interrater agreement on classification of ulcers, and intraclass correlation coefficient (ICC) was used to assess agreement on ulcer area. Because the traditional ICC calculations relied on a small number of ulcers, ICCs were recalculated using the results of linear mixed models to evaluate the variance components of observations on all the data. Intrarater kappa for classifying DU as not an ulcer/healed ulcer versus active/indeterminate ulcer was substantial (0.76), and interrater kappa was moderate (0.53). The ICC for ulcer area using the linear mixed models was moderate both for intrarater (0.57) and interrater (0.48) measurements. A consensus for the classification of DUs in SSc was developed, and after a training session, rheumatologists with expertise in SSc are able to reliably classify DUs and to measure ulcer area.