INTRODUCTION
Hidradenitis suppurativa (HS) is an under-diagnosed, disabling skin disease characterized by subcutaneous inflammatory nodules, painful dermal abscesses, fibrosis, draining sinuses, and hypertrophic scars involving the axillae, shoulders, inguinoperineum, nape of the neck, breast areolae, inframammary, and periumbilical area. The disease involves follicular occlusion of the apocrine glands as a primary event followed by secondary bacterial infection. The sinuses can dissect into fascia and muscle, forming tracts in advanced cases. Obesity, acne, comedones, and hirsutism are significant associations.1
Incidence peaks in the second and third decades and declines by the fifth decade.2 The prevalence of HS is approximately 1%. The disease affects less than 200,000 meeting the classification of a rare disease.3 These numbers might reflect failure of early diagnosis and lack of effective therapies. Therefore, epidemiological data supporting undiagnosed HS as a common disease is needed to determine the true prevalence.4
The exact etiology of HS is unclear. Epidemiological data shows the prevalence in women (75%) compared to men (25%).6 The data suggest a hormonal and genetic etiology.1,5 A relationship between smoking and HS lesions was reported in 66.3% of patients, most commonly males.6 A link exists between BMI value and disease severity as 76% of HS patients were obese.6
MATERIALS AND METHODS
A search of the PubMed and Medline databases was conducted to identify articles describing the pathophysiology, pathogenesis of HS and the implications of using biologics. All articles were
published in English. Our search terminology included: “acne inversa; adalimumab; anakinra; biologic; etanercept; hidradenitis suppurativa; infliximab; interleukin-17A; secukinumab; treatment; tumor necrosis factor-alfa; interleukin-12; interleukin-23; and ustekinumab.†The points of relevance were: efficacy and safety of biologics, improvement in Hurley’s stage, and Sartorius score, Dermatology Life Quality Index (DLQI), Physician Global Assessment (PGA), and Visual Analogue Scale (VAS). The findings are discussed in Tables 1-3.
Pathophysiology and Microbiology
The pathophysiology of HS is still unproven. A recent theory hypothesizes that the disease is triggered by an environmental insult in a genetically predisposed individual, which explains why HS can present as sporadic or familial.1,5 Several genetic loci were recognized, but a single causative gene remains unidentified.5 Numerous studies exhibit elevated levels of upregulated pro-inflammatory cytokines (IL-1B, IL-17, TNF-α).8,9 Significant expression of IL-12/Th1 and IL-23/Th17 pathways also supports immune system involvement in HS.7,8 Follicular support system10 defect followed by an insult may cause a commensal skin bacterial response by producing TNF-α, IL-1B, and IL-17. T-cells, neutrophils, macrophages and mast cells influx leads to infundibular hyperkeratosis, follicular occlusion, dilatation of hair follicles, and secondary inflammation in the apocrine glands.11 Bacterial invasion and biofilm formation causes follicular destruction and abscess formation.
Initially, the biofilm forms by reversible binding between bacterial extracellular organelles, outer membrane proteins and epithelial surface.12 Later, the secretion of an extracellular
