Supplementary Material for: The ABC of Hidradenitis Suppurativa: A Validated Glossary on how to Name Lesions

Background: The precise clinical description of skin lesions observed in some patients with hidradenitis suppurativa (HS) can be extremely difficult. Objective: Establishing a validated glossary of terms allowing the best possible description of lesions observed in HS patients. Material and Methods: Five international experts of HS were to assess a series of 25 photos representing typical lesions of this disorder. For each photo, the experts were asked whether naming of the lesions was possible or not and, if yes, by using which noun. Agreement of their responses was calculated using Fleiss's kappa index. Using a Delphi strategy, photos with disagreement were discussed, and photos were reevaluated on the next day. In case of agreement on the impossibility of naming some clinical situations, new terms, to be included into the glossary, were agreed upon. Results: After the first round of photos, agreement between the experts was poor with a kappa index of only 0.33 (95% CI 0.22-0.46). After extensive discussion of cases with disagreement, the kappa index increased on day 2 to 0.75 (95% CI 0.60-0.87), allowing to conclude on good interobserver agreement on terminology. Furthermore, a few clinical situations were identified in which naming with established semantics is so far not possible. For these situations, the terms ‘multicord', ‘multipore', ‘multitunnel' and ‘retraction' were defined. Discussion: This is the first validation of clinical terms used to describe lesions in patients with HS. This should be helpful in better defining the clinical phenotypes observed in this disorder.