An Assessment of Patient-Reported Outcome Measures in Pyoderma Gangrenosum

Background: Clinical trials of pyoderma gangrenosum (PG) have been limited by a lack of standardized outcome measures to assess the efficacy of therapeutic interventions. Hence, our aims were to compare the usefulness of existing patient reported outcome measures (PROMs) to use as a framework for the development of a new validated PROM for PG. We surveyed PG patients who met published Delphi consensus criteria [1] (n = 8) between 2016-2021 at multiple timepoints (total n = 35) using five questionnaires: the Skindex-29, Skindex-16, Dermatology Life Quality Index, Pain Visual Analog Scale, and Patient Global Assessment. Aggregate scores of the questionnaires were highly colinear (r = 0.77-0.96) which demonstrates their construct validity. The remainder of the analysis focused on the Skindex-16 because it had the most content validity—the five questions with the largest coefficients during factor analysis were related to painfulness, unsightliness, and chronicity of PG lesions. Fifty-five out of 465 (11.8%) pairs of questions from the Skindex-16 were highly colinear (r > 0.8). During factor analysis, the model with the lowest root mean squared error contained eight questions which were representative of all three domains in the survey: symptoms, emotions, and function (Cronbach’s alpha > 0.9). These results indicate that there was a large amount of redundancy in the original Skindex-16 when used for PG, i.e. questions can be removed while maintaining high internal reliability. From this pared-down model, focus group-derived domains and questions will be incorporated into a final instrument that can be used for further validation studies.