[Skip to Navigation]
Consensus Statement
March 10, 2021

Global Harmonization of Morphological Definitions in Hidradenitis Suppurativa for a Proposed Glossary

Author Affiliations
  • 1Laboratory of Investigative Dermatology, The Rockefeller University, New York City, New York
  • 2The Rockefeller University, New York City, New York
  • 3Department of Internal Medicine, University of Minnesota, Minneapolis
  • 4Department of Dermatology, University of Minnesota, Minneapolis
  • 5Department of Internal Medicine, Minneapolis VA Health Care System, Minneapolis, Minnesota
  • 6Department of Dermatology, Minneapolis VA Health Care System, Minneapolis, Minnesota
  • 7Department of Dermatology, Penn State Milton S. Hershey Medical Center, Hershey, Pennsylvania
  • 8Division of Dermatology, Department of Medicine, University of Toronto, Toronto, Ontario, Canada
  • 9Division of Dermatology, Women’s College Hospital, Toronto, Ontario, Canada
  • 10Department of Dermatology and Wound Healing, Division of Infection and Immunity, Cardiff University, Cardiff, United Kingdom
  • 11Department of Dermatology, Zealand University Hospital, Roskilde, Denmark
  • 12Department of Medicine, University of Western Ontario, Windsor, Ontario, Canada
  • 13Department of Dermatology, Dessau Medical Center, Brandenburg Medical School Theodor Fontane and Faculty of Health Sciences Brandenburg, Dessau, Germany
  • 14Department of Venereology, Dessau Medical Center, Brandenburg Medical School Theodor Fontane and Faculty of Health Sciences Brandenburg, Dessau, Germany
  • 15Departments of Allergology, Dessau Medical Center, Brandenburg Medical School Theodor Fontane and Faculty of Health Sciences Brandenburg, Dessau, Germany
  • 16Department of Immunology, Dessau Medical Center, Brandenburg Medical School Theodor Fontane and Faculty of Health Sciences Brandenburg, Dessau, Germany
  • 17Department of Dermatology, Mayo Clinic, Rochester, Minnesota
JAMA Dermatol. 2021;157(4):449-455. doi:10.1001/jamadermatol.2020.5467
Key Points

Question  Can morphological definitions of lesions in hidradenitis suppurativa (HS) be harmonized by a panel of international experts in this disease?

Findings  For this consensus statement, qualitative methods and a 3-round modified Delphi-consensus exercise among 31 experts produced acceptable agreement on morphological definitions across 8 primary HS lesion types. These definitions were validated using both qualitative and quantitative methods.

Meaning  The presented consensus morphological definitions are valuable as guidance for reliable lesion identification and terminology in clinical trials and in practice.


Importance  Standard morphological terminology and definitions are vital for identification of lesion types in the clinical trial setting and communication about the condition. For hidradenitis suppurativa (HS), morphological definitions have been proposed by different groups, representing various regions of the world, but no international consensus has been reached regarding such definitions. A lack of globally harmonized terminology and definitions may contribute to poor-quality data collection in clinical trials as well as poor communication among clinicians, investigators, and patients.

Objective  To establish and validate consensus definitions for typical morphological findings for HS lesions.

Methods  This study was conducted from August 2019 to August 2020. A Delphi study technique was used to assess agreement and then resolve disagreement on HS terminology among international experts. After an initial preparation phase, the process consisted of 3 rounds. In each round, participants reviewed preliminary definitions and rated them as “keep, with no changes,” “keep, with changes,” or “remove.” Eight HS primary lesions, including papule, pustule, nodule, plaque, ulcer, abscess, comedo, and tunnel, were selected because they are most frequently used in HS clinician-reported outcome measures. The initial definitions were based on extant literature, and modifications were made between rounds based on qualitative thematic analysis of open-ended responses or discussion. Consensus was defined as greater than 70% to accept a definition. Consensus stability across rounds was defined as less than 15% change in agreement. Reliability was evaluated using the Gwet agreement coefficient. Validation was based on assessment of face validity and stability across rounds.

Results  A total of 31 experts participated. All 8 HS primary lesion definitions achieved greater than 70% consensus by Delphi round 3. Stability was achieved for papule, pustule, and abscess. The Gwet agreement coefficient increased from 0.49 (95% CI, 0.26-0.71) in round 1 to 0.78 (95% CI, 0.64-0.92) in round 3. Face validity was supported by expert endorsement to keep terms in survey responses. Previously unmeasured variation among clinicians’ definition of tunnels was identified, and consensus was achieved.

Conclusions and Relevance  An international group of experts agreed on definitions for morphological features of HS lesions frequently included in HS clinical trials. These international consensus terms and definitions are needed to support consistency of lesion identification and quantification in clinical trials.

Add or change institution
Limit 200 characters
Limit 25 characters
Conflicts of Interest Disclosure

Identify all potential conflicts of interest that might be relevant to your comment.

Conflicts of interest comprise financial interests, activities, and relationships within the past 3 years including but not limited to employment, affiliation, grants or funding, consultancies, honoraria or payment, speaker's bureaus, stock ownership or options, expert testimony, royalties, donation of medical equipment, or patents planned, pending, or issued.

Err on the side of full disclosure.

If you have no conflicts of interest, check "No potential conflicts of interest" in the box below. The information will be posted with your response.

Not all submitted comments are published. Please see our commenting policy for details.

Limit 140 characters
Limit 3600 characters or approximately 600 words