Bacterial biofilm in chronic lesions of hidradenitis suppurativa

Microenvironmental host-microbe interactions in chronic inflammatory skin diseases

Several microbiome studies have recently demonstrated microbial dysbiosis in various chronic inflammatory skin diseases, and it is considered an important role in the pathogenesis. Although the role of skin dysbiosis in inflammatory skin diseases is debatable, the local microenvironment is considered essential concerning compositional changes and functional alterations of the skin microbiota. Indeed, various local nutrients (e.g., lipids), pH values, water, oxygen, and antimicrobial peptides may affect the level of skin dysbiosis in these skin diseases. In particular, in atopic dermatitis and hidradenitis suppurativa, significant changes in skin dysbiosis have been associated with local aberrant host immune changes. In this review, the potential pathogenic crosstalk between the host and the microbiota is reviewed in relation to the physical, chemical, and biological microenvironments of various chronic inflammatory skin diseases.

Oral fusidic acid for the treatment of mild-to-moderate hidradenitis suppurativa

BACKGROUND

Hidradenitis suppurativa (HS) is a debilitating inflammatory skin disease. Tetracyclines are one of the few therapeutic options recommended for mild-to-moderate disease. This study aimed to investigate the efficacy of systemic fusidic acid's (FA) effectiveness in treating HS.

METHODS

This retrospective study analyzed 55 FA therapy cycles (TC, average weekly dose: 6409 mg; range: 5250-9800 mg; 2-12 weeks) in 49 patients. The outcome was evaluated using the Physician's Global Assessment (PGA) scale. Therapy response was defined as any reduction of inflammatory activity without the occurrence of flares. We also characterized adverse events and investigated predictors for treatment success. Results were compared to a matched control group receiving doxycycline.

RESULTS

FA treatment (55 treatment cycles (TC); male: 45.5%; female: 54.5%) showed an overall response rate of 70.9% (39 TC). No worsening was observed. Significantly higher response rates were observed in females (83.3%, P = 0.026) and Hurley I (90.9%, P = 0.008). After multivariate adjustment, higher response rates were associated with the Hurley grade (P = 0.046) but not with gender (P = 0.0174). Adverse reactions (21.8% gastrointestinal symptoms) occurred in 27.3% (15 TC) and 46.7% within the first 4 weeks. Similar results were observed in the doxycycline control group (overall response rate: 76.4%).

CONCLUSION

Oral FA is safe and improves symptoms in most patients. HS patients could benefit from oral FA treatment, especially in case of contraindications or resistance to tetracyclines.

Fungal biofilm formation and its regulatory mechanism

Fungal biofilm is a microbial community composed of fungal cells and extracellular polymeric substances (EPS). In recent years, fungal biofilms have played an increasingly important role in many fields. However, there are few studies on fungal biofilms and their related applications and development are still far from enough. Therefore, this review summarizes the composition and function of EPS in fungal biofilms, and improves and refines the formation process of fungal biofilms according to the latest viewpoints. Moreover, based on the study of Saccharomyces cerevisiae and Candida albicans, this review summarizes the gene regulation network of fungal biofilm synthesis, which is crucial for systematically understanding the molecular mechanism of fungal biofilm formation. It is of great significance to further develop effective methods at the molecular level to control harmful biofilms or enhance and regulate the formation of beneficial biofilms. Finally, the quorum sensing factors and mixed biofilms formed by fungi in the current research of fungal biofilms are summarized. These results will help to deepen the understanding of the formation process and internal regulation mechanism of fungal biofilm, provide reference for the study of EPS composition and structure, formation, regulation, group behavior and mixed biofilm formation of other fungal biofilms, and provide strategies and theoretical basis for the control, development and utilization of fungal biofilms.

Gram-negative anaerobes elicit a robust keratinocytes immune response with potential insights into HS pathogenesis

Hidradenitis Suppurativa (HS) is a chronic autoinflammatory skin disease with activated keratinocytes, tunnel formation and a complex immune infiltrate in tissue. The HS microbiome is polymicrobial with an abundance of commensal gram-positive facultative (GPs) Staphylococcus species and gram-negative anaerobic (GNA) bacteria like Prevotella, Fusobacterium and Porphyromonas with increasing predominance of GNAs with disease severity. We sought to define the keratinocyte response to bacteria commonly isolated from HS lesions to probe pathogenic relationships between HS and the microbiome. Type strains of Prevotella nigrescens, Prevotella melaninogenica, Prevotella intermedia, Prevotella asaccharolytica, Fusobacterium nucleatum, as well as Staphylococcus aureus and the normal skin commensal Staphylococcus epidermidis were heat-killed and co-incubated with normal human keratinocytes. RNA was collected and analysed using RNAseq and RT-qPCR. The supernatant was collected from cell culture for protein quantification. Transcriptomic profiles between HS clinical samples and stimulated keratinocytes were compared. Co-staining of patient HS frozen sections was used to localize bacteria in lesions. A mouse intradermal injection model was used to investigate early immune recruitment. TLR4 and JAK inhibitors were used to investigate mechanistic avenues of bacterial response inhibition. GNAs, especially F. nucleatum, stimulated vastly higher CXCL8, IL17C, CCL20, IL6, TNF and IL36γ transcription in normal skin keratinocytes than the GPs S. epidermidis and S. aureus. Using RNAseq, we found that F. nucleatum (and Prevotella) strongly induced the IL-17 pathway in keratinocytes and overlapped with transcriptome profiles of HS patient clinical samples. Bacteria were juxtaposed to activated keratinocytes in vivo, and F. nucleatum strongly recruited murine neutrophil and macrophage migration. Both the TLR4 and pan-JAK inhibitors reduced cytokine production. Detailed transcriptomic profiling of healthy skin keratinocytes exposed to GNAs prevalent in HS revealed a potent, extensive inflammatory response vastly stronger than GPs. GNAs stimulated HS-relevant genes, including many genes in the IL-17 response pathway, and were significantly associated with HS tissue transcriptomes. The close association of activated keratinocytes with bacteria in HS lesions and innate infiltration in murine skin cemented GNA pathogenic potential. These novel mechanistic insights could drive future targeted therapies.

Safety and Effectiveness of Percutaneous Ultrasound-Guided Galvanic Current in Tunnels of Patients with Hidradenitis Suppurativa: A Pilot Study

INTRODUCTION

The recurrent nature of hidradenitis suppurativa (HS), even under maintained systemic treatment, makes it necessary to have effective local treatments; however, the response to these therapies is variable (44-81%). The application of galvanic current (GC) has demonstrated its utility in humans in treating lesions structurally similar to those of HS. With this background, the main objective of this study was to evaluate the efficacy and safety of ultrasound-guided percutaneous GC in inflamed and/or draining tunnels of HS.

METHODS

This was an open study (one-way repeated measures design over time). Patients were evaluated at 4 and 12 weeks after receiving GC. A combined clinical response at week 12 (absence of suppuration/inflammation on examination and clinical interview) was considered the principal variable of efficacy. Adverse effects potentially associated with GC were reported by telephone and at each visit.

RESULTS

Twenty-six patients were included, with a male/female ratio of 5:8. The mean age was 35.84 (13.14) years. At 12 weeks after the administration of GC, a complete response was achieved in 77% (20/26) of the treated lesions. No serious adverse effects were observed, and the mean procedural pain assessed by the numeric rating scale was 0.03 (0.2).

CONCLUSION

GC has proven to be effective and well tolerated in inflamed and draining tunnels of patients with HS.

Retinal Microvascular Alterations in Hidradenitis Suppurativa Patients: A Pilot Study Using Optical Coherence Tomography Angiography

Background: Hidradenitis suppurativa (HS) is a relapsing-remitting inflammatory disease characterized by the progression of asymptomatic nodules to deep-seated lesions and fistula formation that leads to suppuration and scarring. Optical coherence tomography angiography (OCTA) is a new non-invasive imaging technique that carefully analyzes retinal microvasculature networks with high-resolution imaging. Recent studies have demonstrated that retinal vessel density and retinal perfusion reflect systemic inflammatory responses. This study's aim was to analyze OCTA-derived retinal microvasculature parameters to understand if patients affected by HS and without any relevant ocular or systemic comorbidities showed impaired retinal vascular function and morphology. Method: We performed a case-control study of HS patients and age- and sex-matched control cohort. A total of 20 eyes from 10 HS patients and 30 eyes from 15 healthy controls were analyzed, and OCTA-derived microvasculature parameters were compared between groups. Results: OCTA images showed that HS patients, compared to healthy controls, were typically characterized by higher values of the foveal avascular zone (FAZ) both in the superficial capillary plexus (SCP) and in the deep capillary plexus (DCP), and by lower values of vessel density (VD)-SCP, VD-DCP, and vessel length density (VLD)-SCP in the foveal region. These findings partially reflect changes that have been demonstrated in diabetic patients that could be induced by a protracted metabolic or systemic inflammatory dysregulation. Conclusions: In conclusion, OCTA enables large-scale, non-invasive visual screening and follow-up of the retinal vasculature features, providing a new strategy for the prevention and monitoring of visual changes in HS patients.

What should a surgeon know about hidradenitis suppurativa?

Otherwise known as Verneuil's disease, hidradenitis suppurative (HS) is a severe dermatosis of heterogeneous appearance affecting 1% of the population. Its pathophysiology is multifactorial, involving genetic predisposition, inflammatory disorder and environmental elements. Its diagnosis is based on the association of three clinical characteristics: characteristic lesions, typical localizations, and the chronic and recurrent nature of the lesions. Given its diversified aspects, diagnosis can be difficult to achieve. As its manifestations often include abscesses, it is important for the surgeon to know how to detect this pathology. The development of biologics has improved treatment of this disease, treatment that necessitates a multidisciplinary medical and surgical approach involving dermatologists and proctologists as well as surgeons. The objective of this report is to synthesize what a surgeon will need to know so as effectively treat HS patients.

Phage therapy for hidradenitis suppurativa: a unique challenge and possible opportunity for personalized treatment of a complex, inflammatory disease

Phage therapy is an emerging antimicrobial treatment for critical multidrug-resistant pathogens. In this review, the specific potential and challenges of phage therapy for patients with hidradenitis suppurativa (HS) are discussed. This represents a unique challenge as HS is a chronic inflammatory disease, but presenting with acute exacerbations, which have an enormous negative impact on patient's quality of life. The therapeutic arsenal for HS has expanded in the past decade, for example, with adalimumab and several other biologicals that are currently under investigation. However, treatment of HS remains challenging for dermatologists because there are individuals who do not respond to any classes of the current treatment options when used for a first or second time. Furthermore, after several courses of treatment, a patient may lose their response to therapy, meaning long-term use is not always an option. Culturing studies and 16S ribosomal RNA profiling highlight the complex polymicrobial nature of HS lesions. Despite the detection of various bacterial species in lesion samples, several key pathogens, including Staphylococcus, Corynebacterium and Streptococcus, may be potential targets for phage therapy. Using phage therapy for the treatment of a chronic inflammatory disease could potentially provide new insights into the role of bacteria and the immune system in HS development. In addition, it is possible more details on the immunomodulatory effects of phages may come to light.

Skin and Gut Microbiome in Hidradenitis Suppurativa: A Systematic Review

Hidradenitis suppurativa (HS) is a chronic skin disease that significantly impairs the quality of life of affected individuals. The disease is characterized by persistent purulent lesions in specific anatomical areas, and its pathophysiology involves multiple factors, including inflammation, genetics, the microbiome, and environmental components. Recent research suggests a potential role for pathogenic bacteria in HS, highlighting the importance of the communication between the human host and the microbiome in maintaining homeostasis and immune system reactivity. However, the exact mechanisms underlying the gut-skin microbial interactions in HS remain unclear. This systematic review aims to examine the existing literature on the differences in skin and gut microbiome composition between HS patients and healthy controls. The review identifies methodological inconsistencies and calls for further research to elucidate the microbiome's role in HS pathogenesis and to explore new therapeutic interventions. The review highlights the need for advancements in microbiome research methodologies, such as metataxonomics and metagenomics, to improve our understanding of the microbiota's impact on health and disease.

Risk of Chronic Kidney Disease in Hospitalized Patients with Hidradenitis Suppurativa

BACKGROUND

Hidradenitis suppurativa (HS) is associated with several comorbidities such as diabetes mellitus and cardiovascular diseases. These comorbidities are also risk factors for chronic kidney disease (CKD), yet little is known about the risk of CKD in HS patients.

OBJECTIVES

The objective was to study the prevalence of CKD in HS patients.

METHODS

Cross-sectional population-based study using the United States National Inpatient Sample database between January 1, 2002 and December 31, 2012 was performed.

RESULTS

We identified 23,767 hospital admissions for HS patients and 95,068 admissions for age- and gender-matched controls. The prevalence of CKD in HS patients was 6.3% (1,497/23,767) compared to non-HS controls which was 4.3% (4,052/95,068). The association of CKD was strongest in HS patients, who were ≥60 years old, 16.9% (475/2,811), male 7.3% (695/9,556), obese 7.8% (407/5,209), diabetic 12.5% (890/7,105), hyperlipidemic 13.3% (416/3,126), and had cardiovascular diseases 12.5% (631/5,045). The crude odds ratio of CKD in HS patients was 1.5 (95% CI: 1.420-1.605) compared to non-HS patients. The association remained significant after adjusting for important covariates with adjusted odds ratio of CKD in HS patients of 1.1 (95% CI: 1.014-1.176) compared to non-HS patients.

CONCLUSIONS

Our findings show that there is a possible association of HS with CKD. Any signs of CKD should be assessed by a nephrologist as early diagnosis can hopefully prevent further progression.

Systemic Antibiotic Therapy in Hidradenitis Suppurativa: A Review on Treatment Landscape and Current Issues

Hidradenitis suppurativa (HS) is a chronic, recurrent, and inflammatory skin disease characterized by painful, deep-seated, nodules, abscesses, and sinus tracts in sensitive areas of the body, including axillary, inguinal, and anogenital regions. Antibiotics represent the first-line pharmacological treatment of HS because of their anti-inflammatory properties and antimicrobial effects. This narrative review summarizes the most significant current issues on the role of systemic antibiotics in the management of HS, critically analyzing the main limits of their use (antibiotic resistance and toxicity). Although, in the last decades, several cytokines have been implicated in the pathomechanism of HS and the research on the use of novel biologic agents in HS has been intensified, antibiotics remain a valid therapeutic approach. Future challenges regarding antibiotic therapy in HS comprise their use in association with biologics in the management of acute flare or as a bridge therapy to surgery.

New Insight into the Molecular Pathomechanism and Immunomodulatory Treatments of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is an immune-mediated inflammatory disorder characterized by deep-seated nodules, abscesses, sinus tracts and scars localized in the intertriginous areas. It is accompanied by pain, malodourous secretion and a dramatically decreased quality of life. Although the pathogenesis has not been entirely elucidated, the primary event is follicular hyperkeratosis of the pilosebaceous apocrine unit. Since the registration of the tumor necrosis factor-alpha inhibitor Adalimumab in 2015, several cytokines have been implicated in the pathomechanism of HS and the research of novel therapeutic targets has been intensified. We provide an update on the inflammatory cytokines with a central role in HS pathogenesis and the most promising target molecules of future HS management.

Confocal microscopy and optical coherence tomography of inflammatory skin diseases in hairs and pilosebaceous units: A systematic review

Common skin disorders such as acne vulgaris, rosacea and folliculitis are bothersome prevalent inflammatory diseases of hair follicles that can easily be investigated bedside using optical coherence tomography (OCT) and reflectance confocal microscopy (RCM) with micrometre resolution, opening a novel era for high-resolution hair follicle diagnostics and quantitative treatment evaluation. EMBASE, PubMed and Web of Science were searched until 5 January 2023 to identify all studies imaging hair follicle characteristics by RCM and OCT for diagnosis and monitoring of treatment in hair follicle-based skin disorders. This study followed PRISMA guidelines. After inclusion of articles, methodological quality was assessed using the QUADAS-2 critical appraisal checklist. Thirty-nine in vivo studies (33 RCM and 12 OCT studies) were included. The studies focused on acne vulgaris, rosacea, alopecia areata, hidradenitis suppurativa, folliculitis, folliculitis decalvans, lichen planopilaris, discoid lupus erythemasus, frontal fibrosing alopecia and keratosis pilaris. Inter- and perifollicular morphology including number of demodex mites, hyperkeratinization, inflammation and vascular morphology could be assessed by RCM and OCT in all included skin disorders. Methodological study quality was low, and interstudy outcome variability was high. Quality assessment showed high or unclear risk of bias in 36 studies. Both RCM and OCT visualize quantitative features as size, shape, content and abnormalities of hair follicles, and have potential to support clinical diagnosis and evaluate treatment effects. However, larger studies with better methodological quality are needed to implement RCM and OCT directly into clinical practice.

Consistency of Bacterial Triggers in the Pathogenesis of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is an inflammatory skin disease whose pathogenesis remains poorly defined. Over the past decades, the bacterial role in HS patients has been a focus of research. According to the literature, the HS skin (and probably gut) bacterial composition is different to that of healthy controls. To date, a key question is whether compositional changes in the microbial populations are responsible for the development of HS (primum movens), or only secondarily reflect the ongoing inflammatory process. The great diversity of methodologies that have been used to study microbial role in HS have led to an accumulation of conflicting results. Thus, in view of these considerations, the aim of this article is to provide the reader with an overview about different hypotheses proposed to explain the bacterial role in HS pathogenesis.

The biofilm life cycle: expanding the conceptual model of biofilm formation

Bacterial biofilms are often defined as communities of surface-attached bacteria and are typically depicted with a classic mushroom-shaped structure characteristic of Pseudomonas aeruginosa. However, it has become evident that this is not how all biofilms develop, especially in vivo, in clinical and industrial settings, and in the environment, where biofilms often are observed as non-surface-attached aggregates. In this Review, we describe the origin of the current five-step biofilm development model and why it fails to capture many aspects of bacterial biofilm physiology. We aim to present a simplistic developmental model for biofilm formation that is flexible enough to include all the diverse scenarios and microenvironments where biofilms are formed. With this new expanded, inclusive model, we hereby introduce a common platform for developing an understanding of biofilms and anti-biofilm strategies that can be tailored to the microenvironment under investigation.

Microbiome in Hidradenitis Suppurativa—What We Know and Where We Are Heading

Recently, interest in the microbiome of cutaneous diseases has increased tremendously. Of particular interest is the gut-brain-skin axis proposed by Stokes and Pillsbury in 1930. The microbiome has been suggested in the pathogenesis of hidradenitis suppurativa, however the link between the commensals and the host is yet to be established. Across all studies, the increased abundance of Porphyromonas, Peptoniphilus, and Prevotella spp., and a loss of skin commensal species, such as Cutibacterium in HS lesions, is a consistent finding. The role of gut and blood microbiome in hidradenitis suppurativa has not been fully elucidated. According to studies, the main link with the intestine is based on the increased risk of developing Crohn’s disease and ulcerative colitis, however, further research is highly needed in this area. Lifestyle, dietary approaches, and probiotics all seem to influence the microbiome, hence being a promising modality as adjuvant therapy. The aim of this review was to present the latest reports in the field of research on skin, blood, and gut microbiome in terms of hidradenitis suppurativa.

Innate immunity and microbial dysbiosis in hidradenitis suppurativa - vicious cycle of chronic inflammation

Hidradenitis Suppurativa (HS) is a chronic multifactorial inflammatory skin disease with incompletely understood mechanisms of disease pathology. HS is characterized by aberrant activation of the innate immune system, resulting in activation of pathways that aim to protect against pathogenic microorganisms, and also contribute to failure to resolve inflammation. Imbalance in innate immunity is evident in deregulation of host antimicrobial peptides (AMPs) and the complement system associated with the microbiome dysbiosis. The pathology is further complicated by ability of pathogens associated with HS to overcome host immune response. Potential roles of major AMPs, cathelicidin, defensins, dermcidin, S100 proteins, RNAse 7 and complement proteins are discussed. Dysregulated expression pattern of innate immunity components in conjunction with bacterial component of the disease warrants consideration of novel treatment approaches targeting both host immunity and pathogenic microbiome in HS.

Novel Diagnostic Technologies and Therapeutic Approaches Targeting Chronic Wound Biofilms and Microbiota

Purpose of Review

To provide an up-to-date overview of recent developments in diagnostic methods and therapeutic approaches for chronic wound biofilms and pathogenic microbiota.

Recent Findings

Biofilm infections are one of the major contributors to impaired wound healing in chronic wounds, including diabetic foot ulcers, venous leg ulcers, pressure ulcers, and nonhealing surgical wounds. As an organized microenvironment commonly including multiple microbial species, biofilms develop and persist through methods that allow evasion from host immune response and antimicrobial treatments. Suppression and reduction of biofilm infection have been demonstrated to improve wound healing outcomes. However, chronic wound biofilms are a challenge to treat due to limited methods for accurate, accessible clinical identification and the biofilm's protective properties against therapeutic agents. Here we review recent approaches towards visual markers for less invasive, enhanced biofilm detection in the clinical setting. We outline progress in wound care treatments including investigation of their antibiofilm effects, such as with hydrosurgical and ultrasound debridement, negative pressure wound therapy with instillation, antimicrobial peptides, nanoparticles and nanocarriers, electroceutical dressings, and phage therapy.

Summary

Current evidence for biofilm-targeted treatments has been primarily conducted in preclinical studies, with limited clinical investigation for many therapies. Improved identification, monitoring, and treatment of biofilms require expansion of point-of-care visualization methods and increased evaluation of antibiofilm therapies in robust clinical trials.

Mechanism of anti-inflammatory effects of Rifampicin in an ex vivo culture system of Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease of the hair follicles leading to painful lesions, associated with increased levels of pro-inflammatory cytokines. Numerous guidelines recommend antibiotics like clindamycin and rifampicin in combination, as first-line systemic therapy in moderate to severe forms of inflammation. HS has been proposed to be mainly an auto-inflammatory disease associated with but not initially provoked by bacteria. Therefore, it has to be assumed that the pro-inflammatory milieu previously observed in HS skin is not solely dampened by the bacteriostatic inhibition of DNA-dependent RNA polymerase. To further clarify the mechanism of anti-inflammatory effects of rifampicin, ex vivo explants of lesional HS from 8 HS patients were treated with rifampicin, and its effect on cytokine production, immune cells as well as the expression of Toll-like receptor 2 (TLR2) were investigated. Analysis of cell culture medium of rifampicin treated HS explants revealed an anti-inflammatory effect of rifampicin that significantly inhibiting interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumour necrosis factor (TNF) -α production. Immunohistochemistry of the rifampicin-treated explants suggested a tendency for it to reduce the expression of TLR2 while not affecting the number of immune cells.

Bacterial biofilms predominate in both acute and chronic human lung infections

Background

A basic paradigm of human infection is that acute bacterial disease is caused by fast growing planktonic bacteria while chronic infections are caused by slow-growing, aggregated bacteria, a phenomenon known as a biofilm. For lung infections, this paradigm has been thought to be supported by observations of how bacteria proliferate in well-established growth media in the laboratory—the gold standard of microbiology.

Objective

To investigate the bacterial architecture in sputum from patients with acute and chronic lung infections.

Methods

Advanced imaging technology was used for quantification and direct comparison of infection types on fresh sputum samples, thereby directly testing the acute versus chronic paradigm.

Results

In this study, we compared the bacterial lifestyle (planktonic or biofilm), growth rate and inflammatory response of bacteria in freshly collected sputum (n=43) from patient groups presenting with acute or chronic lung infections. We found that both acute and chronic lung infections are dominated by biofilms (aggregates of bacteria within an extracellular matrix), although planktonic cells were observed in both sample types. Bacteria grew faster in sputum from acute infections, but these fast-growing bacteria were enriched in biofilms similar to the architecture thought to be reserved for chronic infections. Cellular inflammation in the lungs was also similar across patient groups, but systemic inflammatory markers were only elevated in acute infections.

Conclusions

Our findings indicate that the current paradigm of equating planktonic with acute and biofilm with chronic infection needs to be revisited as the difference lies primarily in metabolic rates, not bacterial architecture.

Human skin microbiota in health and disease: The cutaneous communities' interplay in equilibrium and dysbiosis: The cutaneous communities' interplay in equilibrium and dysbiosis

Cutaneous microbial composition is driven by the microenvironment of the skin, as well as by internal and external factors. Local changes in the microenvironment can affect the configuration of the community, which may lead toward an imbalance of microbiota. Alterations in the microbial profile are common in both inflammatory skin diseases and chronic infections. A shift in balance within the microbiota, toward limited variation and a greater abundance of specific pathogens, may further worsen the pathogenicity of the diseases. These alterations may be prevented by topical treatment of probiotic solutions stimulating a balanced multispecies community. Compositional variations may further constitute potential biomarkers to predict flares or monitor efficacy during therapy. New approaches such as machine learning may contribute to this prediction of microbial alterations prior to the development of chronic infections and flares. This review provides insight into the composition and distribution of a healthy community of microorganisms in the skin and draws parallels with the community in chronic infections and chronic inflammatory skin diseases such acne vulgaris and Hidradenitis Suppurativa. We discuss the potential role of specific species in the pathogenesis and the possible prevention of disease exacerbation.

Hidradenitis Suppurativa: Host-Microbe and Immune Pathogenesis Underlie Important Future Directions

Hidradenitis suppurativa (HS) is an inflammatory disease of the skin with a chronic, relapsing-remitting course. The pathogenesis of the disease is poorly understood and involves multiple factors, including genetics, environment, host-microbe interactions, and immune dysregulation. In particular, the composition of the cutaneous microbiome shifts as the disease progresses, although it is unclear whether this is a primary or secondary process. Trials with immunomodulatory therapy elucidate the role of specific immune pathways and cytokine signaling in disease mechanism, such as TNF-α, IL-1β, IL-12, IL-17, IL-23, and complement. Future studies should continue examining the causes of and contributing factors to microbial changes and immune dysregulation in HS pathogenesis.

New perspectives on the treatment of hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by the presence of painful nodules, abscesses, chronically draining fistulas, and scarring in apocrine gland-bearing areas of the body. The exact pathogenesis of HS is not yet well understood, but there is a consensus in considering HS a multifactorial disease with a genetic predisposition, an inflammatory dysregulation, and an influence of environmental modifying factors. Therapeutic approach of HS is challenging due to the wide clinical manifestations of the disease and the complex pathogenesis. This review describes evidence for effectiveness of current and emerging HS therapies. Topical therapy, systemic treatments, biological agents, surgery, and light therapy have been used for HS with variable results. Adalimumab is the only US Food and Drug Administration (FDA) approved biologic agent for moderate-to-severe HS, but new therapeutic options are being studied, targeting different specific cytokines involved in HS pathogenesis. Comparing treatment outcomes between therapies is difficult due to the lack of randomized controlled trials. Treatment strategy should be selected in concordance to disease severity and requires combination of treatments in most cases.

The Clinical Relevance of the Microbiome in Hidradenitis Suppurativa: A Systematic Review

Hidradenitis suppurativa is a chronic disease of the pilosebaceous unit. The name of the condition is a testament to the presumed relationship between the disease and the microbiome. The pathophysiology of hidradenitis suppurativa is, however, complex and believed to be the product of a multifactorial interplay between the interfollicular epithelium, pilosebaceous unit, microbiome, as well as genetic and environmental factors. In this review we assimilate the existing literature regarding the role played by the human microbiome in HS in various contexts of the disease, including the pathophysiologic, therapeutic, and potentially, diagnostic as well prognostic. In conclusion, the role played by the microbiome in HS is extensive and relevant and can have bench-to-bedside applications.

Single-Cell RNA Sequencing Reveals Cellular and Transcriptional Changes Associated With M1 Macrophage Polarization in Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by recurrent abscesses, nodules, and sinus tracts in areas of high hair follicle and sweat gland density. These sinus tracts can present with purulent drainage and scar formation. Dysregulation of multiple immune pathways drives the complexity of HS pathogenesis and may account for the heterogeneity of treatment response in HS patients. Using transcriptomic approaches, including single-cell sequencing and protein analysis, we here characterize the innate inflammatory landscape of HS lesions. We identified a shared upregulation of genes involved in interferon (IFN) and antimicrobial defense signaling through transcriptomic overlap analysis of differentially expressed genes (DEGs) in datasets from HS skin, diabetic foot ulcers (DFUs), and the inflammatory stage of normal healing wounds. Overlap analysis between HS- and DFU-specific DEGs revealed an enrichment of gene signatures associated with monocyte/macrophage functions. Single-cell RNA sequencing further revealed monocytes/macrophages with polarization toward a pro-inflammatory M1-like phenotype and increased effector function, including antiviral immunity, phagocytosis, respiratory burst, and antibody-dependent cellular cytotoxicity. Specifically, we identified the STAT1/IFN-signaling axis and the associated IFN-stimulated genes as central players in monocyte/macrophage dysregulation. Our data indicate that monocytes/macrophages are a potential pivotal player in HS pathogenesis and their pathways may serve as therapeutic targets and biomarkers in HS treatment.

Hidradenitis suppurativa: A folliculotropic disease of innate immune barrier dysfunction?

The innate immune system of human skin consists of a multi-layered barrier consisting of cells and soluble effector molecules charged with maintaining homeostasis and responding to insults and infections. It has become increasingly clear that these barrier layers become compromised in skin diseases, especially in disorders of an (auto)inflammatory nature. In the case of hidradenitis suppurativa, great strides have been made in recent years in characterizing the underlying breakdown in homeostatic innate immunity, including an increasing understanding of the central role of the hair follicle in this process. This breakdown appears to occur at multiple levels: the pilosebaceous unit, associated epithelium, the cutaneous microbiome, alteration of immune cell function and local molecular events such as complement activation. This review seeks to summarize, contextualize and analyse critically our current understanding of how these innate immune barriers become dysregulated in the early stage(s) of hidradenitis suppurativa, and to speculate on where potential hidradenitis suppurativa research could be most fruitful.

Hidradenitis Suppurativa: Where We Are and Where We Are Going

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease primarily affecting apocrine gland-rich areas of the body. It is a multifactorial disease in which genetic and environmental factors play a key role. The primary defect in HS pathophysiology involves follicular occlusion of the folliculopilosebaceous unit, followed by follicular rupture and immune responses. Innate pro-inflammatory cytokines (e.g., IL-1β, and TNF-α); mediators of activated T helper (Th)1 and Th17 cells (e.g., IFN-γ, and IL-17); and effector mechanisms of neutrophilic granulocytes, macrophages, and plasma cells are involved. On the other hand, HS lesions contain anti-inflammatory mediators (e.g., IL-10) and show limited activity of Th22 cells. The inflammatory vicious circle finally results in pain, purulence, tissue destruction, and scarring. HS pathogenesis is still enigmatic, and a valid animal model for HS is currently not available. All these aspects represent a challenge for the development of therapeutic approaches, which are urgently needed for this debilitating disease. Available treatments are limited, mostly off-label, and surgical interventions are often required to achieve remission. In this paper, we provide an overview of the current knowledge surrounding HS, including the diagnosis, pathogenesis, treatments, and existing translational studies.

[Pathogenesis of hidradenitis suppurativa/acne inversa]

Hidradenitis suppurativa/acne inversa (HS) has a multifactorial pathogenesis. In addition to a sporadic form, a familial form is reported in around 40% of patients, for whom an autosomal dominant (AD) inheritance with reduced gene penetrance is assumed. The phenotype of the disease with inflammatory nodules, abscesses and secreting sinus tracts suggests an infectious origin, but the exact role of the bacteria detected in HS pathogenesis remains unclear. Smoking and metabolic syndrome are regarded as important trigger factors in HS, with obesity and hormonal changes playing a pathogenic role in the latter. Ultimately, Toll-like receptors, antimicrobial peptides, immune cells and key cytokines are involved in the excessive inflammatory reaction of HS and are also the targets of future therapies.

The Burden of Hidradenitis Suppurativa Signs and Symptoms in Quality of Life: Systematic Review and Meta-Analysis

Hidradenitis suppurativa (HS) is a chronic, recurrent and debilitating inflammatory skin disease of the hair follicle that usually presents as painful, deep-seated inflamed lesions in the apocrine gland-bearing areas of the body. HS patients suffer from uncomfortable signs and symptoms, such as pain, pruritus, malodour and suppuration, which may impair patients’ quality of life (QoL). Although HS patients frequently experience these signs and symptoms, they are only occasionally assessed by clinicians and, unexpectedly, the scientific evidence available is limited and heterogeneous. The aim of this study is to summarize the evidence regarding the impact of HS signs and symptoms on QoL to serve as a basis for future research and help clinicians to consider them in the daily care of HS patients. A systematic review and meta-analysis were conducted following PRISMA Guidelines. The following search algorithm was used: (hidradenitis or “acne inversa”) and (pain or itch or odour or malodour or suppuration or oozing or drainage) and (“quality of life”). The literature search identified 836 references, 17 of them met the eligible criteria and were included for analysis, representing 4929 HS patients. Mean age of the participants was 36.28 years and there was a predominance of female sex among study participants. The BMI of the population was in the range of over-weight and about two out five patients were active smokers. Studies included patients with mild to moderate HS, with a mean disease duration of 13.69 years. The HS signs and symptoms assessed were pain, pruritus, malodour and suppuration. Overall, the higher intensity of a sign or symptom correlated with poorer general QoL or specific QoL dimensions including sexual distress, anxiety, depression and sleep. The most frequently employed tool to assess QoL was the Dermatology Life Quality Index (DLQI). DLQI was used in 52.9% of the studies (9/17) with a mean value of 10.70 (2.16 SD). The scores employed to assess signs and symptoms severity were subjective and varied between studies, being the numerical rating scale (NRS) for each of the most used symptoms. The mean NRS value for pain was 3.99 and the mean NRS for pruritus was 4.99. In conclusion, we have summarized, categorized and analyzed the scientific evidence regarding signs and symptoms in HS patients and their impairment in QoL. Their assessment should be thorough and included during routine evaluation of HS patients to motivate therapeutic modifications and increase patients’ health.

Epithelialized tunnels are a source of inflammation in hidradenitis suppurativa

BACKGROUND

Hidradenitis suppurativa (HS), also known as acne inversa, is a chronic, painful, and burdensome inflammatory disease manifesting in nodules and abscesses, with progression to chronically draining tunnels in later-stage disease.

OBJECTIVE

We sought to determine whether HS tunnels are immunologically active participants in disease activity.

METHODS

Skin biopsy specimens were obtained by using ultrasound guidance in untreated patients with HS and those enrolled in an open-label study of brodalumab (ClinicalTrials.gov identifier NCT03960268) for patients with moderate-to-severe HS.

RESULTS

Immunohistochemistry of HS biopsy specimens demonstrated that the epithelialized HS tunnels recapitulate the psoriasiform epidermal hyperplasia morphology of the overlying epidermis, displaying molecular inflammation, including S100A7 (psoriasin) positivity, as well as features of epidermal skin, including loricrin, filaggrin, lipocalin-2, and Melan-A positive cells. Tunnels were associated with increased infiltration of T cells, dendritic cells, and neutrophils; formation of neutrophil extracellular traps, and increased expression of psoriasiform proinflammatory cytokines. Unsupervised hierarchical clustering demonstrated a separation of HS samples based on the presence or absence of tunnels. Tunnels isolated by microdissection had higher levels of epithelium-derived inflammatory cytokines compared with the overlying epidermis and healthy controls. Clinically, the size and draining of the tunnels were decreased with treatment with the IL-17RA antagonist brodalumab.

CONCLUSION

These data suggest that tunnels are a source of inflammation in HS.

Yin and Yang: A disrupted skin microbiome and an aberrant host immune response in hidradenitis suppurativa

The skin microbiome plays an important role in maintaining skin homeostasis by controlling inflammation, providing immune education and maintaining host defense. However, in many inflammatory skin disorders the skin microbiome is disrupted. This dysbiotic community may contribute to disease initiation or exacerbation through the induction of aberrant immune responses in the absence of infection. Hidradenitis suppurativa (HS) is a complex, multifaceted disease involving the skin, innate and adaptive immunity, microbiota and environmental stimuli. Herein, we discuss the current state of HS skin microbiome research and how microbiome components may activate pattern recognition receptor (PRR) pathways, metabolite sensing pathways and antigenic receptors to drive antimicrobial peptide, cytokine, miRNA and adaptive immune cell responses in HS. We highlight the major open questions that remain to be addressed and how antibiotic therapies for HS likely influence both microbial burden and inflammation. Ultimately, we hypothesize that the two-way communication between the skin microbiome and host immune response in HS skin generates a chronic positive feed-forward loop that perpetuates chronic inflammation, tissue destruction and disease exacerbation.

Treatment of hidradenitis suppurativa with tetracycline, doxycycline, or lymecycline: a prospective study

AIM

To evaluate the clinical efficacy of tetracycline, doxycycline, and lymecycline in patients with hidradenitis suppurativa (HS).

METHODS

A prospective study of three different treatment regimens in patients with HS; oral tetracycline 500 mg twice daily, oral doxycycline 100 mg twice daily, and oral lymecycline 300 mg twice daily were administered in patients with HS. Outcomes were change in Hidradenitis Suppurativa Score (HSS), Dermatology Life Quality Life index (DLQI), overall disease-related distress, boil-related pain, number of boils in the preceding month, fraction of patients with no boils in the preceding month, and Physician's Global Assessment (PGA) score at follow-up.

RESULTS

In total, 108 patients, 73 (67.6%) women and 35 (32.4%) men, were included. Mean duration of treatment was 4.3 months. The mean HSS at baseline was 26.10 (SD 20.18) points, improving to 17.97 (SD 17.88) at follow-up, difference is 8.13 (95% CI 5.21-10.93), P < 0.0001. Highest improvement in HSS was observed in the tetracycline group. After multivariate adjustment, higher reduction in HSS was significantly associated with lower BMI, Hurley stage III, higher HSS at baseline, and higher number of boils in the preceding month at baseline.

CONCLUSION

Oral treatment with tetracycline, doxycycline, and lymecycline appears effective and safe in HS patients. Tetracycline provided the greatest clinical improvement measured by HSS.

The Microbiome in Hidradenitis Suppurativa: A Review

INTRODUCTION

Hidradenitis suppurativa (HS) is a chronic autoinflammatory skin disease. It is characterised by the development of abscesses and nodules in intertriginous anatomical sites. Whilst it is now recognised as an autoinflammatory condition rather than an infective disease, bacteria are implicated in disease pathogenesis.

METHODS

We performed a search of the literature from inception to 12 August 2020 using the search terms "hidradenitis suppurativa", "Verneuil's disease", "acne inversa", "microbiome", "bacteriology" and "microbiology". Studies were included if they assessed the cutaneous, gut or oral bacteria, bacteriology or microbiome in hidradenitis suppurativa.

RESULTS

Twenty-one studies examining the cutaneous microbiome and two studies examining the gastrointestinal microbiome in HS were identified. No studies examining the oral microbiome in HS were identified. A total of 972 patients and 46 healthy controls were included across studies examining the cutaneous microbiome. A total of 100 patients and 36 controls were included across both gut microbiome studies. Coagulase-negative Staphylococcus, anaerobes such as Porphyromonas and Prevotella, and Staphylococcus aureus species were commonly encountered organisms across the included cutaneous microbiome studies. The studies examining the gut microbiome were limited, with one small study demonstrating an alteration in the gut microbiome composition compared to controls. The other study found no alteration to the gut microbiome in patients with HS compared to those with inflammatory bowel disease (IBD) and HS, and IBD and/or psoriasis.

CONCLUSION

Research should be undertaken into the oral microbiome in HS. Further research should be undertaken examining the cutaneous and gut microbiome in HS, and its relationship with documented co-morbidities. Additionally, metagenomics-focused studies may help identify the relationship between microorganisms and host, and this may shed light on new pathways of disease pathogenesis. This may help identify potential future therapeutic targets.

Cytokine Pathways and Investigational Target Therapies in Hidradenitis Suppurativa

Background: Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease affecting areas with a high density of apocrine glands and characterized by subcutaneous nodules that may evolve into fistulas with pus secretion. Methods: The aim of this review is to investigate all current knowledge on cytokine regulation in the pathogenesis of HS. A systematic literature research using the words “cytokine”, “interleukin”, “pathway”, and “hidradenitis suppurativa” was performed in PubMed/Medline and Scopus/Embase databases. A search of the clinicaltrials.gov website for interventional recruiting and completed trials including the term “hidradenitis suppurativa” was also performed up to August 2020. We will discuss the pathogenetic role of various cytokines in HS and potential therapeutic targets for this debilitating disease. Results: The pathophysiology underlying this complex condition has not been clearly defined. An upregulation of various cytokines, such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-1, IL-17, IL-23, and other molecules seems to be related to this inflammatory condition. Various cells, such as lymphocytes T Helper 1 and 17 and keratinocytes seem to be involved in the genesis of this condition. Conclusions: Several future studies and clinical trials are necessary in order to have new knowledge about HS and to properly treat this complex condition.

Lymecycline vs. clindamycin plus rifampicin in hidradenitis suppurativa treatment: clinical and ultrasonography evaluation

BACKGROUND

Antibiotic therapy remains the first-line treatment for hidradenitis suppurativa (HS). However, literature data on its comparative clinical efficacy and safety are limited.

AIM

To investigate the efficacy of tetracycline (lymecycline 300 mg daily) vs. the combination therapy clindamycin and rifampicin (600 mg plus 600 mg daily) by evaluating and comparing the clinical response at the end of antibiotic treatment (10 weeks).

METHODS

The study retrospectively analysed 52 patients divided in two groups of 26 patients: Group A received lymecycline and Group B received clindamycin plus rifampicin for 10 weeks. Subjects had mild, moderate and severe HS. The clinical and ultrasonography extent of disease was measured by the Hurley Score, Sonographic Score of Hidradenitis Suppurativa, International Hidradenitis Suppurativa Severity Score System (IHS4), pain visual analogue scale (pain VAS) and Dermatology Life Quality Index (DLQI). The primary outcome was the clinical response at the end of the antibiotic treatment period, according to the Hidradenitis Suppurativa Clinical Response measure.

RESULTS

Both groups showed a significant improvement in IHS4, pain VAS and DLQI from baseline, but this was more marked in Group A. Reductions in nodule counts were similar between the two groups, whereas the number of abscesses and draining tunnels decreased more in Group B. Disease-free survival was similar between the two groups.

CONCLUSION

Lymecycline monotherapy and clindamycin plus rifampicin combination are both effective treatments for patients with moderate-severe HS. Nodular-type HS seems to respond better to lymecycline, whereas the abscess/tunnel type seems to respond better to clindamycin plus rifampicin.

Bacterial aggregate size determines phagocytosis efficiency of polymorphonuclear leukocytes

The ability of bacteria to aggregate and form biofilms impairs phagocytosis by polymorphonuclear leukocytes (PMNs). The aim of this study was to examine if the size of aggregates is critical for successful phagocytosis and how bacterial biofilms evade phagocytosis. We investigated the live interaction between PMNs and Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli and Staphylococcus epidermidis using confocal scanning laser microscopy. Aggregate size significantly affected phagocytosis outcome and larger aggregates were less likely to be phagocytized. Aggregates of S. epidermidis were also less likely to be phagocytized than equally-sized aggregates of the other three species. We found that only aggregates of approx. 5 μm diameter or smaller were consistently phagocytosed. We demonstrate that planktonic and aggregated cells of all four species significantly reduced the viability of PMNs after 4 h of incubation. Our results indicate that larger bacterial aggregates are less likely to be phagocytosed by PMNs and we propose that, if the aggregates become too large, circulating PMNs may not be able to phagocytose them quickly enough, which may lead to chronic infection.

A systematic review and critical appraisal of metagenomic and culture studies in hidradenitis suppurativa

Hidradenitis suppurativa (HS), also known as acne inversa, is a chronic inflammatory skin disease with still largely unknown pathogenesis. While infectious organisms have been identified in lesions of the disease since the 1980s, questions remain over the role that bacteria and microbiome play. Recent studies using 16S ribosomal RNA gene sequencing and larger culture-based studies have begun to paint a clearer picture of the microbial world of HS. With this systematic review, we summarize all the work that has been done to date in HS bacteriology, analyse potential pitfalls and limitations of the current studies, and address future directions of investigation. This systematic review attempted to collate and analyse all bacteriology studies done to date. This review was prospectively registered with PROSPERO (1670769) performed in line with the PRISMA checklist. Twenty two studies were identified comprising 862 individual HS patients for culture studies and 206 HS patients for 16S rRNA gene sequencing studies. Methodology tended to be varied, with different sampling, culturing and sequencing methods as well as amount of analysis and stratification of patients. Bacteria identified as elevated in HS lesions in sequencing studies as well as grown from HS lesions in culture studies are identified and discussed. These primarily included the anerobic Gram-negative bacilli Prevotella, Porphyromonas and Fusibacterium, the Gram-positive bacilli Corynebacterium, and the Gram-positive cocci Staphylococcus, Streptococcus and Parvimonas. Potential interactions, as well as work in other disease models with related bacteria are also discussed. Areas of further investigation include in vitro studies of interactions between bacteria and keratinocytes, gut and oral microbiome studies and deep sequencing studies for virulence and phage factors.

Bacterial biofilm is associated with higher levels of regulatory T cells in unaffected hidradenitis suppurativa skin

BACKGROUND

The role of bacterial biofilm in hidradenitis suppurativa (HS) is highly debated. Less biofilm is found in clinically unaffected axillary perilesional skin of HS patients compared with healthy controls.

OBJECTIVE

To study the correlation between biofilm and the phenotypical characterization of the preclinical inflammatory infiltrate.

MATERIALS AND METHODS

An exploratory comparative study of punch biopsies from unaffected axillary HS skin compared to similarly biopsies from healthy controls underwent standard staining procedures for CD4, CD8, CD25, FoxP3 and IL17. Standard-sized inflammatory histological hotspots were identified manually. Slides were scanned into Leica Biosystems' Digital Image Hub. Number of stained cells per slide and hotspot was found using an algorithm.

RESULTS

12.5% of HS had biofilm compared to 85% of controls. For full slides, HS patients had more CD4+ cells than controls; HS patients with biofilm had higher CD4+ cell number than controls with or without biofilm and HS patients without biofilm. For hotspots, HS patients with biofilm had higher number of CD4+FoxP3+ cells than HS patients without biofilm and controls with biofilm.

CONCLUSION

The association between biofilm and the number of regulatory T cells in HS patients supports the concept of dysbiosis as a factor in the preclinical HS lesions.

Hidradenitis suppurativa is an autoinflammatory keratinization disease: A review of the clinical, histologic, and molecular evidence

The pathogenic model of hidradenitis suppurativa is in the midst of a paradigm shift away from a disorder of primary follicular occlusion to an autoinflammatory keratinization disease. Observational, experimental, and therapeutic evidence supports the concept of hidradenitis suppurativa as a primarily inflammatory disorder, a disorder of autoimmunity, or both, in contrast to the current prevailing paradigm of primary follicular occlusion. The lack of reliable and high-fidelity disease models has limited the available experimental and mechanistic evidence to support or refute one pathogenic model over another. This scholarly review synthesizes the existing clinical, histologic, and molecular data to evaluate the extant evidence supporting the autoinflammatory paradigm and further informing the molecular mechanisms of hidradenitis suppurativa pathogenesis. Follicular hyperkeratosis/occlusion and perifollicular inflammation coexist in histologic specimens, with interleukin 1α demonstrated to stimulate comedogenesis in the infundibulum. pH elevation in occluded body sites alters the microbiome and amplifies existing T-helper cell type 17 immunoresponses. Known metabolic comorbidities and smoking are known to upregulate interleukin 1α in follicular keratinocytes. Identified genetic variants may alter epidermal growth factor receptor signaling, leading to upregulated keratinocyte inflammatory responses. The process of follicular rupture and dermal tunnel formation can be explained as secondary responses to inflammatory activation of fibroblasts and epithelial-mesenchymal transition, with antibody production associated with inflammatory amplification in advanced disease. This review aims to reevaluate and integrate the current clinical, histologic, and molecular data into a pathogenic model of hidradenitis suppurativa. This is essential to advance our understanding of the disease and identify novel therapeutic targets and approaches.

Emerging medical treatments for hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory disease affecting intertriginous skin areas, and it is characterized by recurrent painful episodes of inflammatory drainage. Although the pathophysiology of HS is not fully understood, recent research points to an imbalance of cytokines as a contributing factor to the associated symptoms of purulent drainage and sinus tract formation. HS lesions are often characterized by a superimposed pathogenic/commensal bacterial infection that can improve with targeted antibiotic therapy. New medical treatments have emerged in recent years, many of which specifically work against a variety of proinflammatory mediators associated with HS. These newer, specified treatment options, in conjunction with surgery and lasers, are thought to provide positive outcomes and an overall improvement in quality of life in patients with HS.

Hidradenitis suppurativa

Hidradenitis suppurativa (HS; also designated as acne inversa) is a chronic inflammatory disorder, which affects the intertriginous skin and is associated with numerous systemic comorbidities. The estimated prevalence of HS is ~1% in most studied countries. Typically starting in early adulthood, cutaneous inflamed nodules, abscesses and pus-discharging tunnels develop in axillary, inguinal, gluteal and perianal body sites. The comorbidities of HS include metabolic and cardiovascular disorders, which contribute to reduced life expectancy. A genetic predisposition, smoking, obesity and hormonal factors are established aetiological factors for HS. Cutaneous changes seem to start around hair follicles and involve activation of cells of the innate and adaptive immune systems, with pivotal roles for pro-inflammatory cytokines such as tumour necrosis factor, IL-1β and IL-17. The unrestricted and chronic immune response eventually leads to severe pain, pus discharge, irreversible tissue destruction and scar development. HS has profound negative effects on patients' quality of life, which often culminate in social withdrawal, unemployment, depression and suicidal thoughts. The therapeutic options for HS comprise antibiotic treatment, neutralization of tumour necrosis factor and surgical intervention together with lifestyle modification. Nevertheless, there is an enormous need for awareness of HS, understanding of its pathogenesis and novel treatments.