Aetiology
HS is a multifactorial disease with genetic, environmental, lifestyle, and hormonal components. These factors lead to immune activation around the terminal hair follicles and hyperkeratosis.
HS is not an infectious disease, but bacterial propagation in the intertriginous skin, particularly within the occluded hair follicle units, catalyses immune activation. Inflammation in HS eventually results in extensive pus formation, irreversible tissue destruction, and scar development.[19]
Pathophysiology
HS immunopathogenesis is complex and has characteristics of a neutrophilic dermatosis, with contribution from type 1 helper cells (TH1) and TH17 cells.[19] These activated immunological pathways lead to insufficient anti-microbial defence, pus formation, and extracellular matrix degradation, contributing to plugging of hair follicles, and recurrent inflammation. Painful nodules and abscesses rupture over time causing sinus tracts and scarring, and progressive tissue destruction.[19]
Patients frequently have metabolic syndrome, type 2 diabetes mellitus, atherosclerosis, spondyloarthritis or spondyloarthropathy, inflammatory bowel disease, and depression.[20][21][22][23] Cardiovascular disease is also increased in people with HS, and contributes to increased mortality rates.[19]
Classification
Hurley classification[4][5][6]
The severity of HS can be classified based on the configuration of inflammatory lesions and scars. This method is widely used to stratify disease severity at initial presentation. It is useful to guide treatment choice.[4][5][6]
Hurley stage I (mild): presence of abscesses and inflammatory nodules but without scarring. [Figure caption and citation for the preceding image starts]: Hidradenitis suppurativa stage I: discrete inflamed nodules and papules with intervening normal skin and lack of scarringFrom R.A. Lee, MD, PhD [Citation ends].
Hurley stage II (moderate): presence of abscesses and inflammatory nodules with scarring. However, inflammatory lesions and scars are separated by areas of intervening normal skin. [Figure caption and citation for the preceding image starts]: Hidradenitis suppurativa stage II: inflamed nodules and scars with areas of intervening normal skinFrom R.A. Lee, MD, PhD [Citation ends].
Hurley stage III (severe): extensive interconnected scars with or without active inflamed lesions. [Figure caption and citation for the preceding image starts]: Hidradenitis suppurativa stage III: interconnected scars, cysts, comedones, and inflamed nodulesFrom R.A. Lee, MD, PhD [Citation ends].
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