International HS Severity Scoring System (IHS4) – a new scoring system for Hidradenitis suppurativa (HS) and Acne Inversa

Development and validation of IHS4, a novel dynamic scoring system to assess hidradenitis suppurativa/acne inversa severity

A validated tool for the dynamic severity assessment of hidradenitis suppurativa (HS) is lacking. The aim of this study was to develop and validate such a novel scoring system.


A Delphi voting procedure was conducted among the members of the European Hidradenitis Suppurativa Foundation (EHSF) to achieve consensus towards an initial HS Severity Score System (HS4). Strengths and weaknesses of HS4 were examined by a multicenter prospective study. Multivariate logistic regression, discriminant analysis and receiver operating characteristic curves and examination for correlation (Spearman’s rho) and agreement (Cohen’s kappa) with existing scores were engaged to recognize the variables for a new International HS Severity Scoring System (IHS4) that was established by a 2nd Delphi round.


Consensus HS4 was based on the number of skin lesions, the number of skin areas involved and the Dermatology Life Quality Index and was evaluated by a sample of 236 patients from 11 centers. Subsequently, a multivariate regression model calculated adjusted odds ratios for several clinical signs. Nodules, abscesses and draining tunnels resulted as the scoring variables. Three candidate scores were presented to the 2nd Delphi round. The resulting IHS4 score is calculated by the number of nodules (multiplied by 1) + the number of abscesses (multiplied by 2) + the number of draining tunnels (multiplied by 4). A total score of 3 or less signifies mild, 4-10 signifies moderate and 11 or higher signifies severe disease. Cohen’s kappa was fair (κ=0.317) compared with Hurley classification and moderate (κ=0.493) compared with Expert Opinion. Correlation was good (rho>0.6) with Hurley classification, Expert Opinion, Physician’s Global Assessment and Modified Sartorius score and moderate for Dermatology Life Quality Index (rho=0.356).


The novel IHS4 is a validated tool to dynamically assess HS severity and can be used both in real-life and the clinical trials setting.



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