Complement activation in hidradenitis suppurativa: a new pathway of pathogenesis?

BACKGROUND

Despite the heavy purulence observed in hidradenitis suppurativa (HS), the kinetics of complement anaphylatoxins acting to prime chemotaxis of neutrophils has not been studied.

OBJECTIVES

To explore complement activation in HS.

METHODS

Circulating concentrations of complement factor C5a, as well as of membrane attack complex C5b-9, were determined in the plasma of 54 treatment-naïve patients and of 14 healthy controls, as well as in the pus of seven patients. Results were correlated with Hurley stage and International Hidradenitis Suppurativa Severity Score. Peripheral blood mononuclear cells (PBMCs) were isolated from seven patients with Hurley stage III HS and seven healthy volunteers and stimulated in the presence of 25% of plasma for the production of tumour necrosis factor-α (TNF-α).

RESULTS

Circulating C5a and C5b-9 were significantly greater in patient than in control plasma; however, concentrations in pus were very low. Circulating C5a levels exceeding 28 ng mL^-1 were associated with a specificity > 90% with the occurrence of HS. Circulating levels of C5a and C5b-9 were greater in patients with more severe HS. PBMCs of patients produced high concentrations of TNF-α only when growth medium was enriched with patient plasma; this was reversed with the addition of the C5a blocker IFX-1.

CONCLUSIONS

Systemic complement activation occurs in HS and may be used as a surrogate biomarker of HS. C5a stimulates overproduction of TNF-α and may be a future therapeutic target.

Development and validation of the International Hidradenitis Suppurativa Severity Score System (IHS4), a novel dynamic scoring system to assess HS severity

BACKGROUND

A validated tool for the dynamic severity assessment of hidradenitis suppurativa/acne inversa (HS) is lacking.

OBJECTIVES

To develop and validate a novel dynamic scoring system to assess the severity of HS.

METHODS

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 multicentre prospective study. Multivariate logistic regression, discriminant analysis and receiver operating characteristic curves, as well as examination for correlation (Spearman's rho) and agreement (Cohen's kappa) with existing scores, were engaged to recognize the variables for a new International HS4 (IHS4) that was established by a second Delphi round.

RESULTS

Consensus HS4 was based on number of skin lesions, number of skin areas involved and Dermatology Life Quality Index (DLQI), and was evaluated by a sample of 236 patients from 11 centres. 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 second Delphi round. The resulting IHS4 score is arrived at by the number of nodules (multiplied by 1) plus the number of abscesses (multiplied by 2) plus 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 = 0·32) compared with Hurley classification, and moderate (κ = 0·49) compared with Expert Opinion. Correlation was good (ρ > 0·6) with Hurley classification, Expert Opinion, Physician's Global Assessment and Modified Sartorius score, and moderate for DLQI (ρ = 0·36).

CONCLUSIONS

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.