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Unified Morphological Definitions in Hidradenitis Suppurativa Defined by International Experts

An international group of 31 experts in hidradenitis suppurativa (HS) reached consensus agreements on the definitions for morphological features of HS lesions, clarifying terms frequently evaluated in HS clinical trials. The results of the consensus were published in JAMA Dermatology.

While standard morphologic terminology and definitions are necessary for clear communication about the condition, HS previously had no international consensus regarding such definitions. This lack of consensus may “contribute to poor-quality data collection in clinical trials as well as poor communication among clinicians, investigators, and patients,” the authors noted.

From August 2019 to August 2020, the expert group conducted a Delphi study to assess agreement and then resolve disagreement on HS terminology among. The process had 3 rounds not including an initial preparation phase. Within these rounds, participants reviewed preliminary definitions and rated them as keep, with no changes, keep, with changes, or remove. Eight HS primary lesions, most frequently used in clinician-reported outcome measures and based on use in the literature, were selected: papule, pustule, nodule, plaque, ulcer, abscess, comedo, and tunnel. The group made modifications to the definitions based on qualitative thematic analysis of open-ended responses or discussion. Consensus was defined as greater than 70% to accept a definition, and consensus stability across rounds was defined as less than 15% change in agreement. Validation was based on assessment of face validity and stability across rounds.

Per the results, all eight HS primary lesion definitions achieved greater than 70% consensus by Delphi round 3, and stability was achieved for papule, pustule, and abscess. Reliability increased across rounds, as defined as the Gwet agreement coefficient (0.49 [95% CI, 0.26-0.71] in round 1 vs 0.78 [95% CI, 0.64-0.92] in round 3). During the study, a previously unmeasured variation of the definition of tunnels was identified, and consensus on the definition was achieved by the study conclusion.

The study concluded these international consensus terms and definitions are needed to support consistency of lesion identification and quantification in clinical trials. —Jessica Garlewicz


Frew JW, Lowes MA, Goldfarb N, et al. Global harmonization of morphological definitions in hidradenitis suppurativa for a proposed glossary. JAMA Dermatol. Published online March 10, 2021. doi:10.1001/jamadermatol.2020.5467

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