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Abstracts from the Second International Hidradenitis Suppurativa Research Symposium March 5, 2009 • San Francisco, CA Which HS key issues remain unanswered? Viewpoint: Two Key Issues Jean Revuz Private Practice, Paris, France. There are two key issues to address: • The contradiction between anatomical locations of the disease (i.e. apocrine zones) and the histological features of absence of early involvement of apocrine glands. There is a paucity of data on physiology and pathology of apocrine glands. One of the main challenges is to identify the specificity of the apocrine follicle in HS. • HS is an auto­inflammatory disease presumably related to alteration in innate immunity in the apocrine follicle. Identification of the specific defect in the TLR­cytokine network should be priority in investigation. Viewpoint: Where should we look for Hidradenitis suppurativa? Lennart Emtestam Department of Dermatology, Karolinska University Hospital, Stockholm, Sweden. The typical histology of hidradenitis suppurativa is the formation of sinus tracts in the dermis and the subcutis, similar to the formation of a inflammation due to a foreign body. Biologically, the cells represent a poorly understood phenomenon involving the infiltrative growth of proliferating non­malignant stem cell like keratinocytes. It is likely that the stem cell like cells emerge due to the influence of unknown local factors. Sinus tract formation may represent an aberrant epidermal repair response executed by activated keratinocytes. The processes progress until the recurring abscesses reach a critical size. The complex of fibroblasts­angiogenetic cells­keratinocytes­inflammatory cells spills on to the surface during expansion. At a point of equilibrium, the hyperactive abscess turns into a draining sinus followed by non­malignant/pseudo­malignant infiltrative growth in the dermis and subcutis. Viewpoint: Through the “hair follicle lens” Ralf Paus Dept. of Dermatology, University of Luebeck, D­23538 Luebeck, Germany & School of Translational Medicine, University of Manchester, Manchester, UK. In a recent “Controversies” feature (Kurzen et al., Exp Dermatol 17:455­72, 2008), some of the pertinent open questions on the pathobiology of HS have been summarized. These include e.g. : • If HS primarily is a chronic inflammatory disorder of the hair follicle epithelium, but not of the apocrine gland, why does it preferentially occur in intertriginous skin rich in apocrine glands? • Why after puberty, and in more women than men? What is the genetic and (neuro­)endocrine basis of this? • What are the initial triggers of follicular occlusion and its tissue­destructive, inflammatory sequelae? Namely, is bacterial superinfection only a secondary event, or are bacterial products already involved in the excessive stimulation of innate immunity signals (e.g. release of antimicrobial peptides and chemokines) from the distal hair follicle epithelium that we have hypothesized to be crucial in HS pathobiology? Hidradenitis Suppurativa Foundation, Inc. • 7895 Via Belfiore #4, San Diego, CA 92129 www.hs­foundation.org • Email: info@hs­foundation.org The Second International HS Research Symposium Abstracts, page 2 • Which compartment of the hair follicle epithelium exactly is the very first “nucleus of HS pathogenesis” (e.g., the periinfundibular, distal outer root sheath [ORS]?) • Is the hyperkeratosis and hyperproliferation of distal ORS keratinocytes one sees early during HS pathogenesis a primary event, or only a consequence of prior inflammatory stimuli? • How does the hair follicle innate immune system in as yet uninvolved intertriginous skin of HS patients differ from that of normal controls? • What exactly is the role of nicotinergic acetyl choline receptors in HS pathobiology? These selected open questions will be discussed on the basis of recent insights into hair follicle immunology and hair follicle neuroendocrinology. Histopathology of “hidradenitis suppurativa” alias acne inversa Klaus Sellheyer, MD Dept. of Dermatology, The Cleveland Clinic Foundation, Cleveland, OH; Nelson Dermatopathology Associates, Atlanta, GA. The term “hidradenitis suppurativa” is firmly entrenched in the dermatological literature although it refers to a false pathogenetic concept. The term was historically coined based merely on the characteristic distribution of the apocrine glands and the anatomical coincidence with the disease process. The herein reported histopathological analysis of 176 specimens of “hidradenitis suppurativa” from 152 patients found at the center stage of the disease not a suppurative inflammation of the apocrine sweat glands but an occlusion of the hair follicles, comparable to acne vulgaris. The disease process starts with follicular hyperkeratosis and dilatation of the follicular infundibula evolving into comedones, comparable to the ones observed in acne vulgaris. At this time, the apocrine glands are not involved. Eventually the dilated follicular infundibulum ruptures and the content spills into the surrounding dermis, evoking an acute inflammatory response in the immediate vicinity of the rupture site. Again, the apocrine glands do not show any signs of involvement nor an indication that they are the anatomical starting point of the sequence of events. If the inflammation remains confined to the immediate vicinity of the hair follicle, over time the initially neutrophilic infiltrate subsides and is gradually replaced by a granulomatous one, often with the addition of multinucleated foreign body giant cells. If, however, the acute inflammatory response following rupture is more florid, a large abscess develops which may extend into the subcutaneous tissue. Apocrine glands near the abscess but not involved by it, are unremarkable. Only by extension of the inflammatory process, apocrinitis evolves and apocrine glands are destroyed. Apocrine glands located further away from the extending abscess are morphologically unremarkable. When extensive tissue destruction has ensued, naked hair shafts, surrounded by an inflammatory infiltrate, are often the only indication that the process started from the hair follicle. In an attempt of the tissue to confine the inflammatory reaction and to prevent further spread, remnants of the hair follicle epithelium proliferate and sinus tracts form, often surrounded by fibrosis. The sinus tracts communicate with the surface. Upon bacterial superinfection, they rupture and the process becomes self­maintaining and enters into a vicious cycle. Sinus tract formation is the main reason for the chronicity of the disease and why radical surgery is the only therapeutic option capable of achieving long­lasting cure. Thus, “hidradenitis suppurativa” is a disorder that shares histopathological and clinical aspects with acne vulgaris modified under the special circumstances of anatomical regions rich in apocrine glands. It is acne inversa because in contrast to acne vulgaris the disease involves intertriginous localizations and not the regions classically affected by acne. Autoimmune mechanisms in the pathogenesis of HS Evangelos J. Giamarellos­Bourboulis, MD, PhD 4th Department of Internal Medicine, University of Athens, Medical School, Greece. There is accumulating body of evidence suggesting that patients with HS have severe derangements of their innate immune system. This evidence is based on monocyte stimulation assays and on the favorable clinical responses with biological therapies. Blood monocytes were isolated from 53 patients and stimulated with lipopolysacchraride (LPS) of Escherichia coli O144:H4 (1). Defective monocyte responses characterized by reduced production of tumor necrosis factor­alpha (TNF_) and interleukin­6 (IL­6) were found. In the same study, it was shown that NK cells of patients were increased. These findings pointing towards serious derangements of the innate immune responses in the event of HS, led to a prospective, open­label, one arm clinical trial of the administration of etanercept in 10 patients with HS (NCT00329823, www.clinicaltrials.gov) (2). Etanercept was administered at a dose of 50 mg sc once weekly for 12 weeks. Efficacy of treatment was evaluated by the Sartorius score and by the disease activity index. A more than 50% decrease of both The Second International HS Research Symposium Abstracts, page 3 scores compared with baseline was found in seven patients. All patients reported decrease of pain by week 4 whereas the number of fistulas was significantly decreased. Treatment was well­tolerated. Relapse was noted within 4­8 weeks after cessation of therapy. The above findings implicate derangements of the innate immune system as part of the mechanism of pathogenesis of HS. They also point towards autoimmunity as part of its etiology. References 1. Giamarellos­Bourboulis EJ, Antonopoulou A, Petropoulou C, et al. Altered innate and adaptive immune responses in patients with hidradenitis suppurativea. Br J Dermatol: 2007; 156: 51­56. 2. Giamarellos­Bourboulis EJ, Pelekanou E, Antonopoulou A, et al. An open­label phase II study of the safety and efficacy of etanercept for the therapy of hidradenitis suppurativa. Br J Dermatol 2008; 158: 567­572. Hidradenitis suppurativa and bacteria James J. Leyden, MD University of Pennsylvania School of Medicine, Philadelphia, PA. HS has been viewed as an infectious disease in the past and antibiotic therapy has been the most frequently recommended therapy. Recent studies, however, have failed to recover pathogenic bacteria in most cases. Our studies also show that recovery

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